notes

Introduction

Epigraph adapted from Rolf Jacobsen, “Country Roads,” translated by Robert Bly, with change to feminine by permission of Robert Bly, in Robert W. Bly, ed., News of the Universe: Poems of Twofold Consciousness (San Francisco: Sierra Club Books, 1995).

1. Ant population in the ground and litter is estimated at 8 million per hectare in EJ Fittkau, H Klinge 1973, On biomass and trophic structure of the central Amazonian rain forest ecosystem, Biotropica 5: 2–14. Canopy ant population is put at 16 million per hectare by Terry Erwin (personal communication). In total, there are more than 6 trillion ants in a square mile.

2. This isn’t to imply that ants evolve from one of these kinds of societies to the next. Nor do human societies necessarily take this path; for example, even hunter-gatherer bands exist today.

A Brief Primer on Ants

1. In ants, part of the abdomen is united with the thorax, so among ant specialists these body parts are more correctly referred to as the gaster and the trunk (or mesosoma). The waist is formally known as the petiole; it may also have a second segment, called the postpetiole.

2. I have also seen bulldog ants turn to watch me go by before sprinting after me and leaping onto my legs—an undesirable situation given their swordlike stingers. See MW Moffett 2007, Bulldog ants: Lone huntress, National Geographic 211: 140–149.

3. As Deby Cassill puts it, “Our hands have segmented digits (fingers) and a one-segmented palm. Ants have single segmented digits (spines) and multiple segmented palms (tarsi)” (personal communication). See also D Cassill, A Greco, R Silwal, X Wang 2007, Opposable spines facilitate fine and gross object manipulation in fire ants, Naturwissenschaften 94: 326–332.

4. For other examples of “eusocial” animals and a discussion of this term and others, see James T. Costa, The Other Social Insects (Cambridge, MA: Harvard University Press, 2006); and Nigel C. Bennett and Cris G. Faulkes, African Mole-Rats: Ecology and Eusociality (Cambridge: Cambridge University Press, 2000). For views on the original conditions of ants and termites, see BL Thorne, JFA Traniello 2003, Comparative social biology of basal taxa of ants and termites, Annu. Rev. Entomol. 48: 283–306.

5. Benoit Jahyny, personal communication; B Jahyny, S Lacau, JHC Delabie, D Fresneau, Le genre Thaumatomyrmex, cryptique et prédateur spécialiste de Diplopoda Penicillata, in Sistemática, biogeografía y conservación de las hormigas cazadoras de Colombia, ed. E Jiménez, F Fernández, T Milena Arias, FH Lozano- Zambrano (Bogotá: Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, 2007), pp. 329–346.

6. One ant species has dispensed with males entirely; see AG Himler, EJ Caldera, BC Baer, HF Marín, UG Mueller, No sex in fungus-farming ants or their crops, Proc. R. Soc. Lond. Ser. B 276: 2611–2616. Is there a take-home message for feminists from the ant sisterhoods? Probably not. The careers of ants, male or female, queen or worker, are largely immutable. Channeled into an occupation and career path from the onset of adulthood, an ant has few options in life—which brings to mind the sign posted at the entrance of the ant colony in T. H. White’s The Once and Future King: “Everything not forbidden is compulsory.”

7. EO Wilson 2005, Kin selection as the key to altruism: Its rise and fall, Soc. Res. 72: 159–166; EO Wilson, B Hölldobler 2005, Eusociality: Origin and consequences, Proc. Natl. Acad. Sci. 102: 13367–13371. For other views, see P Nonacs, KM Kapheim 2007, Social heterosis and the maintenance of genetic diversity, J. Evol. Biol 20: 2253–2265; and KR Foster, T Wenseleers, FLW Ratnieks 2006, Kin selection is the key to altruism, Trends Ecol. Evol. 21: 57–60.

8. In rare cases genetic differences are critical in caste determination; see KE Anderson, TA Linksvayer, CR Smith 2008, The causes and consequences of genetic caste determination in ants, Myrmecol. News 11: 119–132.

9. Different age classes are referred to as “temporal castes,” though recent work suggests young workers focus on nursing chores not because they are specialists but rather because they are developmentally immature and tend to stay on the brood piles where they are born, while older workers are broadly competent at tasks both inside and outside the nest; see ML Muscedere, TA Willey, JFA Traniello 2009, Age and task efficiency in the ant Pheidole dentata: Young minor workers are not specialist nurses, Anim. Behav. 77: 911–918; and MA Seid, JFA Traniello 2006, Agerelated repertoire expansion and division of labor in Pheidole dentata: A new perspective on temporal polyethism and behavioral plasticity in ants, Behav. Ecol. Sociobiol. 60: 631–644.

10. Edward O. Wilson, Success and Dominance in Ecosystems: The Case of the Social Insects (Oldendorf/Luhe, Germany: Ecology Institute, 1990).

11. CS Moreau, CD Bell, R Vila, SB Archibald, NE Pierce 2006, Phylogeny of the ants: Diversification in the age of angiosperms, Science 312: 101–104; and EO Wilson, B Hölldobler 2005, The rise of the ants: A phylogenetic and ecological explanation, Proc. Natl. Acad. Sci. 102: 7411–7414.

1. Strength in Numbers

1. C. T. Bingham, Hymenoptera, vol. 2, Ants and Cuckoo-Wasps, in The Fauna of British India, Including Ceylon and Burma, ed. W. T. Blanford (London: Taylor & Francis, 1903), p. 161.

2. It’s curious that the largest marauder ants don’t take a role in transporting food; see FD Duncan 1995, A reason for division of labor in ant foraging, Naturwissenschaften 82: 293–296. Similar arguments have been made for why small leafcutter ants ride on foliage carried by their large sisters, though in that case the hitchhikers have other functions (see p. 183).

3. In this book, the term army ant is used to indicate membership in the ant subfamilies Dorylinae, Ecitoninae, and Aenictinae, issues of whether they share a common ancestor aside. For general reviews, see DJC Kronauer 2008, Recent advances in army ant biology, Myrmecol. News 12: 51–65; and WH Gotwald Jr., Army Ants: The Biology of Social Predation (Ithaca, N.Y.: Cornell University Press, 1995). For views on their evolution, see SG Brady 2003, Evolution of the army ant syndrome: The origin and long-term evolutionary stasis of a complex of behavioral and reproductive adaptations, Proc. Natl. Acad. Sci. 100: 6575–6579; and SG Brady, TR Schultz, BL Fisher, PS Ward 2006, Evaluating alternative hypotheses for the early evolution and diversification of ants, Proc. Natl. Acad. Sci. 103: 18172–18177.

4. Herbert Spencer, The Principles of Sociology (New York: Appleton, 1876), 1: 447–600; and WM Wheeler 1911, The ant-colony as an organism, J. Morphol. 22: 307–325. The mid-nineteenth-century German beekeeper Johannes Mehring was perhaps the first to compare colonies (of honeybees) with whole animal bodies; see J Mehring, Das neue Einwesensystem als Grundlage zur Bienenzucht, oder Wie der rationelle Imker den höchsten Ertrag von seinen Bienen erzielt. Auf Selbsterfahrungen gegründet (Frankenthal: Albeck, 1869).

5. See, e.g., Rudolf Virchow, Cellular Pathology, 2nd English ed. (New York: Robert De Witt, 1860), pp. 12–13: “The composition of the major organism, the so-called individual, must be likened to a kind of social arrangement or society, in which a number of separate existences are dependent upon one another, in such a way, however, that each element possesses its own peculiar activity and carries out its own task by its own powers.”

6. Lewis Thomas, The Lives of a Cell (New York: Viking Press, 1974), p. 12.

7. The identity of the signal remains unknown; see EJH Robinson, DE Jackson, M Holcombe, FLW Ratnieks 2005, Insect communication: “No entry” signal in ant foraging, Nature 438: 442.

8. CJ Kleineidam, W Rössler, B Hölldobler, F Roces 2007, Perceptual differences in trail-following leafcutting ants relative to body size, J. Insect Physiol. 53: 1233–1241.

9. The telecommunications industry may one day take advantage of this system of mass communication with a program to, in effect, release digital ants into the telecom network that will leave digital pheromones to reinforce a path where travel is easy. The electronic pheromones will decay over time, so the current best route will always be marked most strongly, limiting traffic tie-ups. See E Bonabeau, C Meyer 2001, Swarm intelligence: A whole new way to think about business, Harvard Business Review 79: 106–114.

10. Unfortunately, most scientists use the word forager to designate any worker outside the nest. It takes care to ascertain whether a worker is searching for food or carrying out such activities as looking for enemies, constructing a trail, or cleaning. Sometimes it’s a matter of probabilities: while workers focus their efforts in areas that are likely to yield food, or even certain kinds of food, they can take on other functions as the need arises, as if a switch has been flipped in their head. For example, in northern Argentina, David Holway, Edward LeBrun, and I observed Ectatomma workers after their nest entrance was inundated: the first workers out of the nest ignored prey insects for several minutes while they cleared the entrance. I have observed Amazon ants switch from “move away from the nest” behavior, in which they ignore food, to a “foraging phase,” in which they search for an ant nest to raid the brood (see chapter 13). Deborah Gordon describes how the first ants to leave a harvester nest each day assessed the local conditions but didn’t return with seeds; the foragers emerged only later (Deborah Gordon, Ants at Work: How an Insect Society Is Organized [New York: Free Press, 1999], p. 34).

11. Webster’s Unabridged defines “army ant” as “any species of ant that goes out in search of food in companies” (Webster’s Unabridged International Dictionary, 2d ed. [New York, 1939]). Foraging “in companies” is the unique and archetypal trait of the three army ant subfamilies, though there are ancillary characteristics widely associated with an army ant “syndrome,” such as group predation (the catching of prey in a group), group retrieval (used to describe both group transport—see chapter 5—and the retrieval of food along a common path), nomadism, queen morphology, and mode of colony foundation (see chapter 4), as originally discussed by EO Wilson 1958, The beginnings of nomadic and group-predatory behavior in ponerine ants, Evolution 12 (1958): 24–36.

12. Group foraging and group hunting are the most common terms, though group too easily conjures the discrete packs (i.e., with circumscribed memberships) of recruited workers characteristic of some “raiding” ant species that shouldn’t be confused with army ants. Certain ants display intermediate strategies between solitary and group foraging, such as the Argentine ant (see chapter 16).

13. KG Facurel, AA Giarettal 2009, Semi-terrestrial tadpoles as vertebrate prey of trap-jaw ants (Odontomachus, Formicidae), Herpetol. Notes 2: 63–66.

14. Several categories of forager (scout) and recruit have been described, such as recruits that find food other than that to which they were recruited, but most of the distinctions seem limited in value. See, e.g., JC Biesmeijer, H de Vries 2001, Exploration and exploitation of food sources by social insect colonies, Behav. Ecol. Sociobiol. 49: 89–99.

15. Admittedly, distinguishing these situations is more easily said than done. Rather than choose their routes at random, for example, solitary foragers may favor sites where they found food before; see, e.g., JFA Traniello, V Fourcassié, TP Graham 1991, Search behavior and foraging ecology of the ant Formica schaufussi: Colony-level and individual patterns, Ethol. Ecol. Evol. 3: 35–47. As a result, multiple workers may come to one place through individual choice, rather than as a result of a coordinated action. It’s also unlikely that foragers take completely independent courses, entirely ignoring any nestmates encountered in their travels; see, e.g., DM Gordon 1995, The expandable network of ant exploration, Anim. Behav. 50: 995–1007. To my mind, as long as workers don’t strongly constrain or guide each other throughout the food search, for all intents and purposes they are acting solitarily.

16. More accurately, no worker travels without guidance from other workers for more than a minute fraction of the span explored by all the participants during the course of a raid.

2. The Perfect Swarm

1. M Moffett 1984, Swarm raiding in a myrmicine ant, Naturwissenschaften 71: 588–590.

2. Many details of this chapter are discussed in MW Moffett 1988, Foraging dynamics in the group-hunting ant, Pheidologeton diversus, J. Insect Behav. 1: 309–331.

3. Chapter 8 will describe the subterranean army ant Dorylus laevigatus, studied since my work on the marauder ant; this ant has raid speeds and travels distances similar to those of the marauder ant.

4. A swarm and column raider like Pheidologeton diversus, P. silenus could also be called a “marauder ant,” but for clarity in this book I restrict this term to diversus. Pheidologeton silenus is in some ways more convergent with army ants: colonies lack stable trails, often abandon half-eaten bonanzas at the end of a raid, and are decisively carnivorous, mostly carving prey into pieces that are then carried by two or three workers. Even with its faster armies, silenus takes less and less diverse food than diversus, with a preference for poky insect larvae. See MW Moffett 1988, Foraging behavior in the Malayan swarm-raiding ant Pheidologeton silenus, Ann. Entomol. Soc. Am. 81: 356–361.

5. MW Moffett 1986, Behavior of the group-predatory ant Proatta butteli, Insectes Soc. 33: 444–457.

6. Other ant species catch prey in a group this way, for example Myrmicaria opaciventris, which has workers that move near their trails in such numbers that they jointly seize prey ten times their length, a tactic similar to that of Proatta, but perhaps with less “sitting” or “waiting”; see A Dejean, B Schatz, M Kenne 1999, How a group foraging myrmicine ant overwhelms large prey items, Sociobiology 34: 407–418. It is unclear in these species whether the ants should be described as foraging as a “group,” in the sense that they may be constrained or guided in some way by their nestmates. That could be the case if workers clump together by actively orienting toward one another or a feature in the environment, as suggested for another species by HC Morais 1994, Coordinated group ambush: A new predatory behavior in Azteca ants, Insectes Soc. 41: 339–342. Alternatively, the ants could ignore each other but, being inactive, end up close enough together to jointly catch prey.

7. A Dejean, C Evraerts 1997, Predatory behavior in the genus Leptogenys: A comparative study, J. Insect Behav. 10: 177–191.

8. The widely spread out searches of the solitary foragers in most large ant colonies tend to result in a steadier intake of food; see D Naug, J Wenzel 2006, Constraints on foraging success due to resource ecology limit colony productivity in social insects, Behav. Ecol. Sociobiol. 60: 62–68.

9. Forget that all the workers in a raid constantly come and go; the effect would be the same if they all stayed within the swarm.

10. Sun Tzu, The Art of War, in Roots of Strategy: The Five Greatest Military Classics of All Time, ed. Thomas Raphael Phillips (Mechanicsburg, Pa.: Stackpole Books, 1985), pp. 21–63.

11. These swarm raiders are essentially all African and American, leaving the marauder ant to occupy the swarm-raider niche in Asia.

12. In a sense, what this means is that not only don’t individuals serve as scouts, but a group of workers can’t jointly serve as a scout for other raids, either. A tactic with some characteristics of mass foraging occurs in species with a trunk trail that rotates gradually at a speed that depends on food availability. See S Goss, J-L Deneubourg 1989, The self-organising clock pattern of Messor pergandei, Insectes Soc. 36: 339–346; and RA Bernstein 1975, Foraging strategies of ants in response to variable food density, Ecology 56: 213–219.

13. See, e.g., H Topoff, J Mirenda, R Droual, S Herrick 1980, Behavioural ecology of mass recruitment in the army ant Neivamyrmex nigrescens, Anim. Behav. 28: 779–789. It could also be that recruitment and exploratory signals are the same, but the pheromone is deposited at a higher concentration and thus is more attractive. Workers in some solitary-foraging species can lay exploratory trails to investigate novel terrain on their own; see, e.g., EO Wilson 1962, Chemical communication among workers of the fire ant Solenopsis saevissim, 1: The organization of mass-foraging, Anim. Behav. 10: 135–147. See also chapter 16.

14. In army ants, the existence of exploratory trails is inferred from the posture of the foragers at the front: each presses her body against the ground in a manner that suggests she is releasing a pheromone on the walking surface; see J Billen, B Gobin 1996, Trail following in army ants, Neth. J. Zool. 46: 272–280. The only solid proof of exploratory trails exists in certain Malayan Leptogenys, currently the best-studied examples of convergence with army ant raids. Leptogenys distinguenda, for example, has swarm raids a few yards wide, and pioneers reaching unmarked ground lay secretions different from recruitment signals to food. See V Witte, U Maschwitz 2002, Coordination of raiding and emigration in the ponerine army ant Leptogenys distinguenda: A signal analysis, J. Insect Behav. 15: 195–217. I predict much more will be learned about foraging strategies from other species of Leptogenys, which show a striking diversity of behaviors up to and including trunk trails and true mass foraging.

15. EC Yip, KS Powers, L Avilés 2008, Cooperative capture of large prey solves scaling challenge faced by spider societies, Proc. Natl. Acad. Sci. USA 105: 11818–11822; and DE Jackson 2007, Social spiders, Curr. Biol. 17: R650–R652.

16. JC Bednarz 1988, Cooperative hunting Harris’ hawks (Parabuteo unicinctus), Science 239: 1525–1527.

17. D Kaiser 2003, Coupling cell movement to multicellular development in myxobacteria, Nat. Rev. Microbiol. 1: 45–54.

18. John T. Bonner, Why Size Matters: From Bacteria to Blue Whales (Princeton: Princeton University Press, 2006).

19. Edward O. Wilson, Sociobiology: The New Synthesis (Cambridge, MA: Harvard University Press, 1975), p. 53.

20. John T. Bonner, The Social Amoebae (Princeton: Princeton University Press, 2008); and JJ Kuzdzal-Fick, KR Foster, DC Queller, JE Strassmann 2007, Exploiting new terrain: An advantage to sociality in the slime mold Dictyostelium discoideum, Behav. Ecol. 18: 433–437.

21. T Nakagaki, H Yamada, Á Tóth 2000, Intelligence: Maze-solving by an amoeboid organism, Nature 407: 470.

22. J Reinhard, M Kaib 2001, Trail communication during foraging and recruitment in the subterranean termite Reticulitermes santonensis, J. Insect Behav. 14: 157–171; and J Reinhard, H Hertel, M Kaib 1997, Systematic search for food in the subterranean termite Reticulitermes santonensis, Insectes Soc. 44: 147–158.

23. Terrence D. Fitzgerald, The Tent Caterpillars (Ithaca, NY: Cornell University Press, 1995).

24. AN Radford, AR Ridley 2006, Recruitment calling: A novel form of extended parental care in an altricial species, Curr. Biol. 16: 1700–1704.

25. TM Judd, PW Sherman 1996, Naked mole-rats recruit colony mates to food sources, Anim. Behav. 52: 957–969.

26. B Heinrich, T Bugnyar 2007, Just how smart are ravens? Sci. Am. 296: 64–71.

27. For humans, see Keith F. Otterman, How War Began (College Station: Texas A&M University, 2004). The two activities commonly share metaphors. See, e.g., David Livingstone Smith, The Most Dangerous Animal: Human Nature and the Origins of War (New York: St. Martin’s Press, 2007); and Bradley A. Thayer, Darwin and International Relations: On the Evolutionary Origins of War and Ethnic Conflict (Lexington: University Press of Kentucky, 2004).

28. The density of army ants tends to be greatest for those species raiding largely underground, presumably because space is cramped there, though they often continue to be concentrated when exposed.

29. William M. Wheeler, Ants: Their Structure, Development, and Behavior (New York: Columbia University Press, 1910), p. 246.

30. JH Fewell 2003, Social insect networks, Science 301: 1867–1870.

31. As expressed in this statement: “Men do not fight for a cause but because they do not want to let their comrades down” (Samuel L.A. Marshall, Men against Fire: The Problem of Battle Command [Washington, D.C.: William Morrow, 1947], pp. 42–43).

32. The only exception I have seen documented is the ant Paraponera, whose workers reportedly identify each other as individuals and also identify one another’s trails; see MD Breed, JM Harrison 1987, Individually discriminable recruitment trails in a ponerine ant, Insectes Soc. 34: 222–226. Another researcher claims that workers identify individuals at times; see Zhanna Reznikova, Animal Intelligence: From Individual to Social Cognition (Cambridge: Cambridge University Press, 2007). This behavior is known for the queens of one ant; see S Dreier, JS van Zweden, P D’Ettorre 2007, Long-term memory of individual identity in ant queens, Biol. Lett. 3: 459– 462. Some ants form dominance hierarchies, but they do so by recognizing not individuals per se but each other’s reproductive or competitive status; see, e.g., J Heinze 2008, Hierarchy length in orphaned colonies of the ant Temnothorax nylanderi, Naturwissenschaften 95: 757–760.

33. The slow growth of army ant colonies, for example, may reflect their high worker death rate; see S Powell 2004, Polymorphism and ecology in the New World army ant genus Eciton, Ph.D. thesis, University of Bristol, England, 2004.

34. M Hammond 1980, A famous “exemplum” of Spartan toughness, Classical J. 75: 97–109.

3. Division of Labor

1. MW Moffett 1986, Marauders of the jungle floor, National Geographic 170: 272–286.

2. Formally, only the minor workers, being a discrete size group, should be called a “caste” in this species; the medias, the majors, and possibly the giants, being distinguished only by their relative frequency in a size continuum, are “subcastes.” Marauder ant division of labor is described in MW Moffett 1987, Division of labor and diet in the extremely polymorphic ant Pheidologeton diversus, Natl. Geogr. Res. 3: 282–304.

3. AL Mertl, JFA Traniello 2009, Behavioral evolution in the major worker subcaste of twig-nesting Pheidole: Does morphological specialization influence task plasticity? Behav. Ecol. Sociobiol. 63: 1411–1426; and EO Wilson 1984, The relation between caste ratios and division of labor in the ant genus Pheidole. Behav. Ecol. Sociobiol. 16: 89–98.

4. See, e.g., DE Wheeler, HP Nijhout 1984, Soldier determination in Pheidole bicarinata: Inhibition by adult soldiers, J. Insect Physiol. 30: 127–135. Caste sizes and frequencies can vary with locality, suggesting evolution to suit local needs: L Passera, E Roncin, B Kaufmann, L Keller 1996, Increased soldier production in ant colonies exposed to intraspecific competition, Nature 379: 630–631.

5. The individuals of a size that is scarce, such as those falling at the midpoint between the peak sizes for media and major workers of Pheidologeton diversus, might carry out the same tasks as workers of the more common sizes but accomplish those tasks relatively poorly, or they may be of a size relatively less often needed. Alternatively, they could execute different tasks than other workers—tasks that happen to require relatively few individuals.

6. Quoted in Drew G. Faust, This Republic of Suffering (New York: Alfred Knopf, 2008), p. 59.

7. Nathan Rosenstein, personal communication. For more examples relating to humans, see Robert L. O’Connell, Ride of the Second Horseman: The Birth and Death of War (New York: Oxford University Press, 1997).

8. U Maschwitz, M Hahn, P Schönegge 1979, Paralysis of prey in ponerine ants, Naturwissenschaften 66: 213–214.

9. MW Moffett 1989, Trap-jaw ants, National Geographic 175: 394–400. Related species have a broader diet; see W Gronenberg, CRF Brandao, BH Dietz, S Just 1998, Trap-jaws revisited: The mandible mechanism of the ant Acanthognathus, Physiol. Entomol. 23: 227–240.

10. SN Patek, JE Baio, BL Fisher, AV Suarez 2006, Multifunctionality and mechanical origins: Ballistic jaw propulsion in trap-jaw ants, Proc. Natl. Acad. Sci. 103: 12787–12792.

11. MW Moffett 1986, Trap-jaw predation and other observations on two species of Myrmoteras, Insectes Soc. 33: 85–99.

12. George F. Oster and Edward O. Wilson, Caste and Ecology in the Social Insects (Princeton: Princeton University Press, 1978), pp. 281–286.

13. This is true for both cold-and warm-blooded animals; see, e.g., AA Heusner 1985, Body size and energy metabolism, Annu. Rev. Nutr. 5: 267–293. James Waters (pers. comm.) found a similar decrease in metabolic rate with colony size in Pogonomyrmex californicus (expressed per capita). My “energy to spare” hypothesis is supported, for example, by the greater metabolic scope available to large animals, i.e., the factor by which basal rate can rise to maximum activity (Steven Vogel, pers. comm.).

14. R Jeanson, JH Fewell, R Gorelick, SM Bertram 2007, Emergence of increased division of labor as a function of group size, Behav. Ecol. Sociobiol. 62: 289–298.

15. See, e.g., JM Herbers 1981, Reliability theory and foraging by ants, J. Theor. Biol. 89: 175–189.

16. T Pham 1924, Sur le régime alimentaire d’une espèce de fourmi Indochinoise (Pheidologeton diversus Ierdon), Ann. Sci. Nat. Zool. 10: 131–135.

17. ML Roonwal 1975, Plant-pest status of root-eating ant, Dorylus orientalis, with notes on taxonomy, distribution, and habits, J. Bombay Nat. Hist. Soc. 72: 305–313.

18. Granivory has in turn been hypothesized to have evolved from carnivory, in areas of limited protein sources; see JH Brown, OJ Reichman, DW Davidson 1979, Granivory in desert ecosystems, Annu. Rev. Ecol. Syst. 10: 201–227.

19. On this military tactic, see Basil H. Liddell Hart, Strategy, 2d ed. (London: Faber & Faber, 1967).

20. Judged by the marauder ant’s cousin, affinis; see SM Berghoff, U Maschwitz, KE Linsenmair 2003, Influence of the hypogaeic army ant Dorylus (Dichthadia) laevigatus on tropical arthropod communities, Oecologia 135: 149–157.

21. Harlan K. Ullman and James P. Wade, Shock and Awe: Achieving Rapid Dominance (Washington, D.C.: Center for Advanced Concepts and Technology, 1996), p. 25.

22. NR Franks, LW Partridge 1993, Lanchester battles and the evolution of combat in ants, Anim. Behav. 45: 197–199.

23. Another extraordinary exception is the jumping spider Portia, which catches a diversity of spider prey; see DP Harland, RR Jackson, Portia perceptions: The umwelt of an araneophagic jumping spider, in Complex Worlds from Simpler Nervous Systems, ed. Frederick R. Prete (Cambridge, MA: MIT Press, 2004), pp. 5–40. For further information on ecological specialization, see DP Vázquez, RD Stevens 2004, The latitudinal gradient in niche breadth: Concepts and evidence, Am. Nat. 164: E1–E19; and DJ Futuyma, G Moreno 1988, The evolution of ecological specialization, Annu. Rev. Ecol. Syst. 19: 207–233.

24. Similar experiments have since been done on a New World army ant—moving prey around in the litter and providing dead insects, for example—showing that the ants can subdivide their swarm raids to create a multipronged search pattern that is more efficient in dealing with food patches; see NR Franks, N Gomez, S Goss, J-L Deneubourg 1991, The blind leading the blind in army ant raid patterns: Testing a model of self-organization, J. Insect Behav. 4: 583–607.

25. Marauder ant raids can begin by recruitment overrun in response to food found on or near a trail by a single worker (chapter 2). Other ants use solitary foragers to investigate areas in this way, including excess recruited ants and ants lost from trails. One army ant in the southwestern United States exhibits similar behavior: after a raid begins to plunder an ant colony for its brood, further column raids spread outward from there in all directions, and as a result the ants often find more nest entrances nearby; see HR Topoff, J Mirenda, R Droual, S Herrick 1980, Behavioural ecology of mass recruitment in the army ant Neivamyrmex nigrescens, Anim. Behav. 28: 779–789.

26. S Garnier, J Gautrais, G Theraulaz 2007, The biological principles of swarm intelligence, Swarm Intell. 1: 3–31; and Marco Dorigo and Thomas Stützle, Ant Colony Optimization (Cambridge, MA: MIT Press, 2004).

27. Charles Darwin, Descent of Man (London: John Murray, 1872), 1: 140.

28. Lewis Thomas, Lives of the Cell (New York: Viking Press, 1974), p. 12; for ant colonies as brains, see W Gronenberg 2008, Structure and function of ant brains: Strength in numbers, Myrmecol. News 11: 25–36.

29. MW Moffett 1987, Ants that go with the flow: A new method of orientation by mass communication, Naturwissenschaften 74: 551–553.

30. DE Jackson, M Holcombe, FLW Ratnieks 2004, Trail geometry gives polarity to ant foraging networks, Nature 432: 907–909.

31. Among trail-laying ants, the density of traffic seldom overwhelms; rather, the push-and-shove causes the workers to add backup routes until the roads are commodious enough to accommodate the traffic; see, e.g., A Dussutour, V Fourcassié, D Helbing, J-L Deneubourg 2004, Optimal traffic organization in ants under crowded conditions, Nature 248: 70–73.

32. Theodore Schneirla, the father of all army ant research, thought that army ants could find their way home in more or less this manner, though he proposed that odor may also influence their directional choices at trail intersections; see Theodore C. Schneirla, Army Ants: A Study in Social Organization (San Francisco: W.H. Freeman, 1971).

33. A more complicated theory of “lane formation” is developed in ID Couzin, NR Franks 2003, Self-organized lane formation and optimized traffic flow in army ants, Proc. R. Soc. Lond. Ser. B 270: 139–146.

34. A John, A Schadschneider, D Chowdhury, K Nishinari 2008, Characteristics of ant-inspired traffic flow, Swarm Intell. 2: 25–41; A Dussutour, J-L Deneubourg, V Fourcassié 2005, Temporal organization of bi-directional traffic in the ant Lasius niger, J. Exp. Biol. 208: 2903–2912; and D Helbing, P Molnár, IJ Farkas, K Bolay 2001, Self organizing pedestrian movement, Envir. Plann. B 28: 361–383.

4. Infrastructure

This chapter derives mostly from MW Moffett, Nesting, emigrations, and colony foundation in two group-hunting myrmicine ants, in Advances in Myrmecology, ed. James C. Trager and George C. Wheeler (New York: EJ Brill, 1989), pp. 355–370; and MW Moffett 1987, Division of labor and diet in the polymorphic species Pheidologeton diversus, Nat. Geogr. Res. 3: 282–304.

1. H Samaniego, ME Moses 2008, Cities as organisms: Allometric scaling of urban road networks, J. Trans. Land Use 1: 21–39; and John Tyler Bonner, The Evolution of Complexity (Princeton: Princeton University Press, 1988). Unlike vertebrate circulatory systems, human highway systems tend to be decentralized, as are trails for species such as the weaver ant (see chapter 9).

2. The lower cost to ants of sticking to clear paths rather than going over rough ground is addressed in JH Fewell 1988, Energetic and time costs of foraging in harvester ants, Pogonomyrmex occidentalis, Behav. Ecol. Sociobiol. 22: 401–408.

3. See, e.g., AS Aleksiev, B Longdon, MJ Christmas, AB Sendova-Franks, NR Franks 2007, Individual choice of building material for nest construction by worker ants and the collective outcome for their colony, Anim. Behav. 74: 559–566.

4. R Beckers, OE Holland, J-L Deneubourg 1994, From local actions to global tasks: Stigmergy and collective robotics, in Artificial Life IV: Proceedings of the Fourth Workshop on the Synthesis and Simulation of Living Systems, ed. Rodney A. Brooks and Pattie Maes (Cambridge, MA: MIT Press, 1994), pp. 181–189. For further examples of stigmergy, see G Theraulaz, J Gautrais, S Camazine, J-L Deneubourg 2003, The formation of spatial patterns in social insects: From simple behaviours to complex structures, Philos. Trans. R. Soc. Lond. Ser. A, 361: 1263–1282; and Thomas D. Seeley, The Wisdom of the Hive (Cambridge, MA: Harvard University Press, 1995).

5. MA Elloitt 2007, Stigmergic collaboration, Ph.D. thesis, University of Melbourne, Australia.

6. Smaller majors also perform the shoving task, but with more limited effectiveness. Such is the irony of being proficient at a job in a society: rather than growing in number as a result, as do urban pigeons adept at building nests on every window ledge, an efficiently run colony gets by with fewer extreme specialists—and possibly, when their duties are rare enough, perilously few; see EO Wilson 1968, The ergonomics of caste in the social insects, Am. Nat. 102: 41–66.

7. DL Cassill, K Vo, B Becker 2008, Young fire ant workers feign death and survive aggressive neighbors, Naturwissenschaften 95: 617–624.

8. For defensive behaviors generally, see A Buschinger, U Maschwitz 1984, Defensive behavior and defensive mechanisms in ants, in Defensive Mechanisms in Social Insects, ed. Henry R. Hermann (New York: Praeger, 1984), pp. 95–150; and MHJ Möglich, GD Alpert 1979, Stone dropping by Conomyrma bicolor: A new technique of interference competition, Behav. Ecol. Sociobiol. 6: 105–113.

9. CJ Lumsden, B Hölldobler 1983, Ritualized combat and intercolony communication in ants, J. Theor. Biol. 100: 81–98.

10. NR Franks, LW Partridge 1993, Lanchester battles and the evolution of combat in ants, Anim. Behav. 45: 197–199; and SD Porter, CD Jorgensen 1981, Foragers of the harvester ant, Pogonomyrmex owyheei: A disposable caste? Behav. Ecol. Sociobiol. 9: 247–256. A sad fact of human military history is that putting the most expendable soldiers in the front lines often pays off. Although the modern military does what it can to protect its soldiers (conducting saturation bombing before sending them in, for example), it is no accident that at the time of this writing, the last war in which a U.S. general died in combat was the Vietnam War—and it was caused by a helicopter crash in dense fog, not enemy fire.

11. Similar shifts back and forth between nests also occur in army ants; see WH Gotwald Jr. 1978, Emigration behavior of the East African driver ant Dorylus (Anomma) molestus, J.N.Y. Entomol. Soc. 86: 290.

12. RS Savage 1847, On the habits of the “drivers” or visiting ants of West Africa, Trans. R. Entomol. Soc. Lond. 5: 1–15; the quotation appears on p. 4.

13. See, e.g., C. Schöning, WM Njagi, NR Franks 2005, Temporal and spatial patterns in the emigrations of the army ant Dorylus (Anomma) molestus in the montane forest of Mt. Kenya, Ecol. Entomol. 30: 532–540; and EO Wilson 1958, The beginnings of nomadic and group-predatory behavior in the ponerine ants, Evolution 12: 24–31.

14. H Topoff, J Mirenda 1980, Army ants on the move: Relation between food supply and emigration frequency, Science 207: 1099–1100. Certain Leptogenys ants that, like diversus, are now known to raid like army ants are thought to have become nomadic prior to evolving into mass foragers, but apparently for a different reason: species of this genus move due to the frequent disturbances they experience from nesting in the leaf litter; see V Witte, U Maschwitz 2002, Coordination of raiding and emigration in the ponerine army ant Leptogenys distinguenda: A signal analysis, J. Insect Behav. 15: 195–217.

15. See, e.g., JM Leroux 1982, Ecologie des populations de dorylines Anomma nigricans dans la région de Lamto (Côte d’Ivoire), Publications du Laboratoire de Zoologie, no. 22, Ecole Normale Supérieure, Paris. One New World army ant has even been recorded encamped at one site for at least eight months; see HG Fowler 1979, Notes on Labidus praedator in Paraguay, J. Nat. Hist. 13: 3–10.

16. J Smallwood 1982, Nest relocations in ants, Insectes Soc. 29: 138–147. Even some large, entrenched colonies can migrate often; see, e.g., HG Fowler 1981, On the emigration of leaf-cutting ant colonies, Biotropica 13: 316.

17. V Witte and U Maschwitz 2008, Mushroom harvesting ants in the tropical rain forest, Naturwissenschaften 95: 1049–1054.

18. In a variant of fission called budding, far less than half the colony departs with a newly crowned queen to start their own colony elsewhere, leaving the original queen with her nest. Terry McGlynn thinks that budding and fission may be widespread among ants with small nests in rainforest leaf litter, where competition can be too intense for queens to start colonies alone. See TP McGlynn 2006, Ants on the move: Resource limitation of a litter-nesting ant community in Costa Rica, Biotropica 38: 419–427. Over much of pre-agricultural human history, hunter-gatherer groups arose in much the same way. Bands split as they grew beyond a few dozen individuals and either began experiencing discord or had trouble searching widely for meals as a foraging group; without infrastructure and stockpiles, such divisions were easy. These groups also fused more readily than do ant colonies. See FW Marlowe 2005, Hunter-gatherers and human evolution, Evol. Anthropol. 14: 54–67.

19. Though specialized egg-carrying by young queens suggests that they are able to start colonies from scratch, a possibility is that marauder ants can also readopt mated queens from their own or other colonies; these queens might then produce colonies by fission or budding (see note 18).

5. Group Transport

1. Much of the information on group transport in this and the next section is from MW Moffett 1992, Group transport and other behavior in Daceton armigatum ants in Venezuela, Nat. Geogr. Res. 8: 220–231; and MW Moffett 1988, Cooperative food transport by an Asiatic ant, Nat. Geogr. Res. 4: 386–394.

2. I am grateful to Jane Goodall, George Schaller, John Eisenberg, and Frans de Waal for these examples.

3. WL Brown Jr. 1960, Contributions toward a reclassification of the Formicidae, III: Tribe Amblyoponini, Bull. Mus. Comp. Zool. 122: 145–230.

4. That’s a problem with wood, too; as a result, beavers often drag logs alone, and termites eat wood on the spot or slice it into bits that they then carry solo. African harvester termites, however, slice grass into appropriately sized segments and, on rare occasions, move them as a group.

5. VS Banschbach, A Brunelle, KM Bartlett, JY Grivetti, RL Yeamans 2006, Tool use by the forest ant Aphaenogaster rudis: Ecology and task allocation, Insectes Soc. 53: 463–471.

6. B Hölldobler 1981, Foraging and spatiotemporal territories in the honey ant Myrmecocystus mimicus, Behav. Ecol. Sociobiol. 9: 301–314.

7. Galileo Galilei, “Dialogues Concerning Two New Sciences” (1638), in On the Shoulders of Giants, ed. Stephen Hawking (Philadelphia: Running Press, 2002), p. 498.

8. John H. Sudd, An Introduction to the Behaviour of Ants (London: Edward Arnold, 1967).

9. Owen Holland, personal communication; J Halloy et al. 2007, Social integration of robots into groups of cockroaches to control self-organized choices, Science 318: 1155–1158; and F Mondada, LM Gambardella, D Floreano, S Nolfi, J-L Deneubourg, M Dorigo 2005, The cooperation of swarm-bots, IEEE Robot. Automat. Mag. 12: 21–28.

10. Even ants that perform rudimentary group transport probably balance their loads at least crudely; see NR Franks 1986, Teams in social insects: Group retrieval of prey by army ants (Eciton burchelli), Behav. Ecol. Sociobiol. 18: 425–429.

11. In most sports, players rotate in and out during a game, so participation isn’t constant; the same holds true for workers entering and leaving a raid. The idea of noninterchangeability as a basis for recognizing “teams” was proposed by George F. Oster and Edward O. Wilson in Caste and Ecology in the Social Insects (Princeton: Princeton University Press, 1978).

12. Originally this model was described for army ant transport teams; e.g., C Anderson, NR Franks 2003, Teamwork in animals, robots, and humans, Adv. Study Behav. 33: 1–48; and NR Franks, AB Sendova-Franks, C Anderson 2001, Division of labour within teams of New World and Old World army ants, Anim. Behav. 62: 635–642. Their descriptions of teams don’t resemble our everyday notions of teams, either the teams people form in which tasks are not done at the same time, as in baseball, or teams in which each player does the same thing, as in bowling.

13. The ant’s name has been changed, having been described as Formica schaufussi in the original research; see SK Robson, JFA Traniello, Key individuals and the organisation of labor in ants, in Information Processing in Social Insects, ed. Claire Detrain, Jean-Louis Deneubourg, and Jacques M. Pasteels (New York: Springer, 1999); and SK Robson, JFA Traniello 1998, Resource assessment, recruitment behavior, and organization of cooperative prey retrieval in the ant Formica schaufussi, J. Insect Behav. 11: 1–22.

14. This army ant behavior is described in the references in note 12.

15. Adam Smith, Wealth of Nations (London: Strahan & Cadell, 1776); see also Emile Durkheim, The Division of Labor in Society (New York: Free Press, 1964).

16. Members of socially complex ant species tend to be simpler than members of simpler societies; e.g., K Jaffe, MJ Hebling-Beraldo 1993, Oxygen consumption and the evolution of order: Negentropy criteria applied to the evolution of ants, Experientia 49: 587–592.

17. J Bequaert 1922, Predaceous enemies of ants, Bull. Am. Mus. Nat. Hist. 45: 271–331.

6. Big Game Hunters

1. Driver ants are classified as the surface-active, swarm-raiding army ant species in Anomma, a subgenus within the genus Dorylus.

2. Ogden Nash, Ogden Nash’s Zoo (New York: Stewart, Tabori & Chang, 1986), p. 41.

3. Y Möbius, C Boesch, K Koops, T Matsucawa, T Humle 2008, Cultural differences in army ant predation by West African chimpanzees? A comparative study of microecological variables, Anim. Behav. 76: 37–45; C Schöning, T Humle, Y Möbius, WC McGrew 2008, The nature of culture: Technological variation in chimpanzee predation on army ants revisited, J. Hum. Evol. 20: 48–59.

4. WH Gotwald Jr. 1984, Death on the march: Army ants in action, Rotunda 17: 37–41.

5. EO Wilson, NI Durlach, LM Roth 1958, Chemical releasers of necrophoric behavior in ants, Psyche 65: 108–114.

6. The segregation of tasks based on size, as occurs in more labor-intensive road-construction activities in the marauder ant, is less evident in driver ants: Caspar Schöning, personal communication; C Schöning, W Kinuthia, NR Franks 2005, Evolution of allometries in the worker caste of Dorylus army ants, Oikos 110: 231–240.

7. Marauders bring in little food during dry spells; however, they cut back foraging accordingly, with few and weaker raids. Driver ant raids are more richly rewarded after rains, when insect abundance skyrockets. But as I later saw for myself on a trip to rainy Ghana, even then escapees are common. In the fifty or so raids I eventually observed of seven driver ant species in Nigeria and Ghana, less than one in a hundred ants, and often more like one in a thousand, returned with food in her jaws, compared to 10 to 40 percent of marauder ants. It may be that some populations are more efficient; according to one report (A Raignier, J van Boven, Étude taxonomique, biologique et biométrique des Dorylus du sous-genre Anomma, Annales du Musée Royal du Congo Belge, n.s. 4, Sciences Zoologiques, vol. 2 [1955]: 1–359), from 7 to 22 percent of Dorylus wilverthi workers carry back food, though Caspar Schöning tells me this estimate seems high.

8. EO Wilson 1958, The beginnings of nomadic and group-predatory behavior in the ponerine ants, Evolution 12: 24–36.

9. This runs contrary to expectations that larger colonies show a steadier food intake and most likely occurs, I believe, because of the nonindependence of raiding ants during mass foraging, which makes an army ant colony the equivalent of a single large animal; see JW Wenzel, J Pickering 1991, Cooperative foraging, productivity, and the central limit theorem, Proc. Natl. Acad. Sci. 88: 36–38.

10. This idea is pursued in WH Gotwald Jr. 1974, Predatory behavior and food preferences of driver ants in selected African habitats. Ann. Entomol. Soc. Am. 67: 877–886.

11. These are not members of the replete caste, just well-fed ordinary workers.

12. Overlapping ideas are discussed for leafcutter ants in J Röschard, F Roces 2003, Cutters, carriers, and transport chains: Distance-dependent foraging strategies in the grass-cutting ant Atta vollenweideri, Insectes Soc. 50: 237–244; JJ Howard 2001, Costs of trail construction and maintenance in the leaf-cutting ant Atta columbica, Behav. Ecol. Sociobiol. 49: 348–356; and F Roces, JA Núñez 1993, Information about food quality influences load-size selection in recruited leaf-cutting ants, Anim. Behav. 45: 135–143.

13. LMA Bettencourt, J Lobo, D Helbing, C Kühnert, GB West 2007, Growth, innovation, scaling, and the pace of life in cities, Proc. Natl. Acad. Sci. 104: 7301–7306.

14. Deborah M. Gordon, Ants at Work: How an Insect Society Is Organized (New York: Free Press, 1999). To study another instance of apparent “counting,” researchers chopped an ant’s legs short or lengthened them with straw to demonstrate that distance traveled was measured by an internal odometer; see M Wittlinger, R Wehner, H Wolf 2006, The ant odometer: Stepping on stilts and stumps, Science 312: 1965–1967.

15. Scott Camazine, Jean-Louis Deneubourg, Nigel R. Franks, James Sneyd, Guy Theraulaz, and Eric Bonabeau, eds., Self-Organization in Biological Systems (Princeton: Princeton University Press, 2001).

16. William F. Joyce, Nitin Nohria, and Bruce Roberson, What Really Works: The 4+2 Formula for Sustained Business Success (New York: HarperCollins, 2003); James Surowiecki, The Wisdom of Crowds: Why the Many Are Smarter than the Few and How Collective Wisdom Shapes Business, Economies, Societies, and Nations (New York: Doubleday, 2003).

17. The idea of homeostasis and its application to both bodies and societies was originally developed in Walter B. Cannon, The Wisdom of the Body, 2d ed. (New York: W. W. Norton, 1939).

18. See, e.g., JW Wenzel, J Pickering 1991, Cooperative foraging, productivity, and the central limit theorem, Proc. Natl. Acad. Sci. 88: 36–38; R Rosengren, W Fortelius, K Lindström, A Luther 1987, Phenology and causation of nest heating and thermoregulation in red wood ants of the Formica rufa group studied in coniferous forest habitats in southern Finland, Ann. Zool. Fenn. 24: 147–155; and Edward O. Wilson, The Insect Societies (Cambridge, MA: Harvard University Press, 1971).

19. Admittedly, these raids include a variety of army ants, which may select different ants as prey. See S O’Donnell, J Lattke, S Powell, M Kaspari 2007, Army ants in four forests: Geographic variation in raid rates and species composition, J. Anim. Ecol. 76: 580–589; and M Kaspari, S O’Donnell 2003, High rates of army ant raids in the Neotropics and implications for ant colony and community structure, Evol. Ecol. Res. 5: 933–939.

20. NR Franks, CR Fletcher 1983, Spatial patterns in army ant foraging and migration: Eciton burchelli on Barro Colorado Island, Panama, Behav. Ecol. Sociobiol. 12: 261–270. Because raids are only a few meters wide, the overlap avoided by foraging in this pattern is very slight, involving only the first few of the many meters traveled from the nest.

21. For army ants, “a long time” is any period longer than the normal length of a raid.

22. Such patches can be exploited even by species otherwise known for harvesting patches of dispersed items; see, e.g., F Lopez, JM Serrano, FJ Acosta 1992, Intense reactions of recruitment facing unusual stimuli in Messor barbarus, Dtsch. Entomol. Z. 39: 135–142.

23. JFA Traniello 1989, Foraging strategies of ants, Annu. Rev. Entomol. 34: 191–210.

24. This defensive function of trunk trails has been described for other ant species, including ones in which foragers travel solitarily from the trails; see B Hölldobler 1976, Recruitment behavior, home range orientation and territoriality in harvester ants, Pogonomyrmex, Behav. Ecol. Sociobiol. 1: 3–44.

25. Whether the ants were drawn in this direction because of the success of the previous day’s raid is an open question. This was one of the four cases I documented in Nigeria in which routes were partially reused after one to three days of neglect. Twice workers reestablished a twisty trail on rocky ground, including sections that had been subterranean.

26. Carl Rettenmeyer told me he saw trail-following of prey by Eciton hamatum many times, but the only published evidence that this is the column raider’s strategy is presented in RL Torgerson, RD Akre 1970, Interspecific responses to trail and alarm pheromones by New World army ants, J. Kans. Entomol. Soc. 43: 395–404.

7. Clash of the Titans

1. Caspar Schöning tells me, however, that springtails show up in driver ant prey samples in Kenya.

2. JT Longino 2005, Complex nesting behavior by two neotropical species of the ant genus Stenamma, Biotropica 37: 670–675.

3. Driver ants would prove to be among the most common chimpanzee prey; see C Schöning, D Ellis, A Fowler, V Sommer 2007, Army ant prey availability and consumption by chimpanzees (Pan troglodytes vellerosus) at Gashaka (Nigeria), J. Zool. 271: 125–133.

4. C Schöning, MW Moffett 2007, Driver ants invading a termite nest: Why do the most catholic predators of all seldom take this abundant prey? Biotropica 39: 663–667. Among the New World army ants, the largest recorded attacks may be the subterranean plunderings of giant leafcutter ant nests; see S Powell, E Clark 2004, Combat between large derived societies: A subterranean army ant established as a predator of mature leaf-cutting ant colonies, Insectes Soc. 51: 342–351.

5. C Seignobos, JP Deguine, HP Aberlenc 1996, Les Mofu et leurs insectes, J. d’Agri. Tradition. Bot. Appl. 33: 125–187.

6. D Inward, G Beccaloni, P Eggleton 2007, Death of an order: A comprehensive molecular phylogenetic study confirms that termites are eusocial cockroaches, Biol. Lett. 3: 331–335.

7. There was an indication that the ants might process termites for short-term storage rather than eating them at once. Termite reproductives were taken to the old nest with their limbs hanging loosely. By the time they were transported to the new nest they resembled streamlined lozenges, each leg and wing having been trimmed. Not that this helped: after the migration, the ants still had more food than they could handle, and the termites piled in the new nest were already starting to stink.

8. The only seeds army ants take are those with elaiosomes, digestible outgrowths similar in composition to insect prey, which plants use to lure ants to carry seeds off without eating the embryo within; see L Hughes, M Westoby, E Jurado 1994, Convergence of elaiosomes and insect prey: Evidence from ant foraging behavior and fatty acid composition, Funct. Ecol. 8: 358–365.

9. The narrow defense function of Eciton soldiers is affirmed by H Topoff, K Lawson, P Richards 1973, Trail following in two species of the army ant genus Eciton: Comparison between major and intermediate-sized workers, Ann. Entomol. Soc. Am. 66: 109–111.

10. Probably the migrations of some army ants are more commonly triggered by problems at the nest (e.g., inserting a stick) than by a dearth of food. Colonies choose a nest site over the course of a few hours at most, necessarily based on limited information. Expropriation by a returning animal, floods, and unstable support branches or cavity walls are likely.

11. For the original report, see A Dejean, PJ Solano, J Ayroles, B Corbara, J Orivel 2005, Insect behaviour: Arboreal ants build traps to capture prey, Nature 434: 973.

12. My research was done on the ant shrub Cordia nodosa, which has arcades that appear identical to those of Hirtella physophora, the host plant to Allomerus decemarticulatus in French Guiana, where the study by Dejean et al. took place (see note 11). For my experiments I used Orthoptera 6 to 15 mm long—all smaller than the grasshopper shown in the photograph in the original study. To determine how well Allomerus used this tactic to catch prey, I forced the issue by holding forty grasshoppers in forceps against a covered trail for fifteen seconds—longer than any healthy insect would stay put while being stung and bitten. All escaped the ants easily thereafter, except a small one, which was killed and eaten. I thank Frederick Prete for advice on the limitations of orthopteran vision and locomotion.

8. Notes from Underground

1. Aldous Huxley, Brave New World Revisited (New York: Harper, 1958), p. 23.

2. A Raignier, J van Boven 1955, Etude taxonomique, biologique et biométrique des Dorylus du sous-genre Anomma, Annales du Musée Royal du Congo Belge, n.s. 4, Sciences Zoologiques 2: 1–359.

3. For Old World army ants, see C Schöning, WM Njagi, NR Franks 2005, Temporal and spatial patterns in the emigrations of the army ant Dorylus (Anomma) molestus in the montane forest of Mt. Kenya, Ecol. Entomol. 30: 532–540. Fights have been documented for Asian subterranean species; see SM Berghoff, J Gadau, T Winter, KE Linsenmair, and U Maschwitz 2003, Sociobiology of hypogaeic army ants: Characterization of two sympatric Dorylus species on Borneo and their colony conflicts, Insectes Soc. 50: 139–147. Also, African Typhlopone army ants are focused predators of driver ants; see JM Leroux 1982, Ecologie des populations de dorylines Anomma nigricans dans la région de Lamto (Côte d’Ivoire), Publications du Laboratoire de Zoologie, no. 22, Ecole Normale Supérieure, Paris.

4. MK Peters, S Likare, M Kraemer 2008, Effects of habitat fragmentation and degradation on flocks of African ant-following birds, Ecol. Appl. 18: 847–858. In tropical America, the birds snatch enough food to reduce the ants’ raid productivity; see PH Wrege, M Wikelski, JT Mandel, T Rassweiler, ID Couzin 2005, Antbirds parasitize foraging army ants, Ecology 86: 555–559.

5. C Schöning, W Njagi, W Kinuthia 2008, Prey spectra of two swarm-raiding army ant species in East Africa, J. Zool. 274: 85–93. For a possible prey specialist army ant, see WH Gotwald Jr. 1978, Trophic ecology and adaptation in tropical Old World ants of the subfamily Dorylinae, Biotropica 10: 161–169.

6. For an excellent experiment on dietary specialization, see A Dejean, B Schatz, J Orivel, G Beugnon, JP Lachaud, B Corbara 1999, Feeding preferences in African ponerine ants: A cafeteria experiment, Sociobiology 34: 555–568.

7. B Schatz, J-P Suzzoni, B Corbara, A Dejean 2001, Selection and capture of prey in the African ponerine ant Plectroctena minor, Acta Oecol. 22: 55–60.

8. Leafcutters are the ultimate example of learned preferences in ants; they tolerate only the single strain of fungus in their own nest and not the strains of their neighbors (see chapter 15).

9. A Dejean, R Fénéron 1999, Predatory behaviour in the ponerine ant, Centromyrmex bequaerti: A case of termitolesty, Behav. Processes 47: 125–133.

10. Because most ants at an army ant raid front are small, size matching during foraging per se may not be significant. Size matching and differences in size preference can occur both within and between colonies of the same and different species; see, e.g., M Kaspari 1996, Worker size and seed size selection by harvester ants in a neotropical forest, Oecologia 105: 397–404; and JFA Traniello, SN Beshers 1991, Polymorphism and size-pairing in the harvester ant Pogonomyrmex badius: A test of the ecological release hypothesis, Insectes Soc. 38: 121–127. The efficiency of polymorphism can be addressed using a “pseudomutant technique” of removing selected size classes. This method has shown that in leafcutter ants, the young colonies contain the minimal size range of workers to perform efficiently; although their division of labor is flexible, a colony with the “optimal” worker size-frequency distribution may still be most efficient; see EO Wilson 1985, The sociogenesis of insect colonies, Science 228: 1489–1495.

11. C Schöning, W Kinuthia, NR Franks 2005, Evolution of allometries in the worker caste of Dorylus army ants, Oikos 110: 231–240; M Kaspari, MD Weiser 1999, The size-grain hypothesis and interspecific scaling in ants, Funct. Ecol. 13: 530–538.

12. SM Berghoff, A Weissflog, KE Linsenmair, R Hashim, U Maschwitz 2002, Foraging of a hypogaeic army ant: A long neglected majority, Insectes Soc. 49: 133–141; SM Berghoff, A Weissflog, KE Linsenmair, M Mohamed, U Maschwitz 2002, Nesting habits and colony composition of the hypogaeic army ant Dorylus (Dichthadia) laevigatus, Insectes Soc. 49: 380–387.

13. A Weissflog, E. Sternheim, WHO Dorow, S Berghoff, U Maschwitz 2000, How to study subterranean army ants: A novel method for locating and monitoring field populations of the South East Asian army ant Dorylus (Dichthadia) laevigatus with observations on their ecology, Insectes Soc. 47: 317–324.

14. Henry Walter Bates, Naturalist on the River Amazon (London: Bradbury & Evans, 1864). As we shall see in chapter 14, this is an example of task partitioning; see C Anderson, FLW Ratnieks 2000, Task partitioning in insect societies: Novel situations, Insectes Soc. 47: 198–199.

15. TD Seeley, PK Visscher 2003, Choosing a home: How the scouts in a honeybee swarm perceive the completion of their group decision making, Behav. Ecol. Sociobiol. 54: 511–520.

16. NR Franks, SC Pratt, EB Mallon, NF Britton, DJT Sumpter 2002, Information flow, opinion polling, and collective intelligence in house-hunting social insects, Philos. Trans. R. Soc. Lond. Ser. B 357: 1567–1584; PK Visscher 2007, Group decision making in nest-site selection among social insects, Annu. Rev. Entomol. 52: 255–275; and Bert Hölldobler and Edward O. Wilson, The Superorganism (New York: W. W. Norton, 2008).

17. J Hickson, SD Yamada, J Berger, J Alverdy, J O’Keefe, B Bassler, C Rinker-Schaeffer 2009, Societal interactions in ovarian cancer metastasis: A quorumsensing hypothesis, Clin. Exp. Metastasis, 26: 67–76.

18. A likely absence of the army ant characteristics of mass foraging and prey carriage in the Nigerian sub may represent an evolutionary loss of those features, given that it is an unidentified species belonging to Dorylus subgenus Dorylus, a group not considered “primitive” (that is, basal to other army ants); see DJC Kronauer, C Schöning, LB Vilhelmsen, JJ Boomsma 2007, A molecular phylogeny of Dorylus army ants provides evidence for multiple evolutionary transitions in foraging niche, BMC Evol. Biol. 7: 56–66.

19. This “looping” behavior was first described for an army ant, but it is widespread among recruiting ants; see H Topoff, J Mirenda, R Droual, S Herrick 1980, Behavioural ecology of mass recruitment in the army ant Neivamyrmex nigrescens, Anim. Behav. 28: 779–789.

20. R Chadab, CW Rettenmeyer 1975, Mass recruitment by army ants, Science 188: 1124–1125.

21. The species was either affinis itself or a close relative. Its subterranean tendencies are documented by M Masayuki, CE Heng, AH Ahmad 2005, Marauder ant (Pheidologeton affinis) predation of green turtle (Chelonia mydas) nest in Chagar Hutang, Redang Island and measures to protect the nests, Proc. 2nd Int. Symp. SEASTAR2000 Asian Bio-logging Sci., 55–62.

22. This is another example of recruitment overrun, which occurs in both mass-foraging and solitary-foraging species. In a similar chain reaction I’ve seen, Solenopsis invicta fire ants will depart from the food to which they’ve been recruited, fanning out as searching individuals to recruit to other food, and sometimes enough are present to catch large prey along the way.

23. Perhaps if I’d been less distracted by affinis, I would also have noticed in the same forest a particular Leptogenys that later was described as having raids convergent with army ants; see, e.g., U Maschwitz, S Steghaus-Kovac, R Gaube, H Hänel 1989, A South East Asian ponerine ant of the genus Leptogenys with army ant life habits, Behav. Ecol. Sociobiol. 24: 305–316.

24. The detailed developmental unfolding of trunk trails is largely unknown. To transition to a raid process, trail production must become disengaged from the discovery of food, as would be the case if foragers departing from them were to employ exploratory trails in their solitary searches for food (see chapter 16). The closest to such an “intermediate” strategy is described for a species well on its way to foraging like an army ant: see FD Duncan, RM Crewe 1994, Group hunting in a ponerine ant, Leptogenys nitida, Oecologia 97: 118–123.

9. Canopy Empires

1. Generally, I won’t distinguish the two species, as their ecology is similar.

2. WH Gotwald Jr. 1972, Oecophylla longinoda, an ant predator of Anomma driver ants, Psyche 79: 348–356.

3. The driver ants’ response was a ratcheted-up version of the runaway reaction that occurs when the big-headed Pheidole dentata ant comes under attack from fire ants and explosively abandons its nest, with hundreds fleeing in all directions; see EO Wilson 1976, The organization of colony defense in the ant Pheidole dentata, Behav. Ecol. Sociobiol. 1: 63–81.

4. More weaver ants are recruited to snatch workers from Dorylus columns than are required to catch the driver ants for food, suggesting the thefts may be defensive; see B Hölldobler 1979, Territories of the African weaver ant (Oecophylla longinoda), Z. Tierpsychol. 51: 201–213.

5. Sloppiness can be good, and it can even be built into the system: the advantage of a honeybee making errors about the direction to which she was recruited is comparable to a navy ship that “should fire salvoes with a considerable scatter, in the hope that at least one shell will hit a hostile ship and slow it down”; see JBS Haldane, H Spurway 1954, A statistical analysis of communication in “Apis mellifera” and a comparison with communication in other animals, Insectes Soc. 1: 247–283. See also RP Fletcher, C Cannings, PG Blackwell 1995, Modelling foraging behaviour of ant colonies, in Advances in Artificial Life, ed. Federico Moran, Alvaro Moreno, Juan J. Merelo, and Pablo Chacón (Berlin: Springer Verlag, 1995), pp. 772–783; and J-L Deneubourg, JM Pasteels, JC Verhaeghe 1983, Probabilistic behaviour in ants: A strategy of errors? J Theor. Biol. 105: 259–271.

6. The living chains superficially resemble those made by army ants to form their nests, except in army ants the workers link toe to toe rather than jaw to waist, and army ant chains are passive—they are not used to pull objects together. Other ants can use their own bodies to make bridges, ladders, flanges, curtains, walls, plugs, rafts, and other constructions. See C Anderson, G Theraulaz, J-L Deneubourg 2002, Self-assemblages in insect societies, Insectes Soc. 49: 99–110; and C Anderson, DW McShea 2001, Intermediate-level parts in insect societies: Adaptive structures that ants build away from the nest, Insectes Soc. 48: 291–301.

7. B Hölldobler, EO Wilson 1983, The evolution of communal nest-weaving in ants, Am. Sci. 71: 490–499.

8. B Hölldobler, CJ Lumsden 1980, Territorial strategies in ants, Science 210: 732–739.

9. RK Peng, K Christian, K Gibb 1998, Locating queen ant nests in the green ant, Oecophylla smaragdina, Insectes Soc. 45: 477–480.

10. In Australia, mature colonies can also have multiple queens; see RK Peng, K Christian, K Gibb 1998, How many queens are there in mature colonies of the green ant, Oecophylla smaragdina?, Aust. J. Entomol. 37: 249–253.

11. ML Smith 2007, Territories, corridors, and networks: A biological model for the premodern state, Complexity 12: 28–35.

12. G Beugnon, A Dejean 1992, Adaptive properties of the chemical trail system of the African weaver ant Oecophylla longinoda, Insectes Soc. 39: 341–346; and A Dejean, G Beugnon 1991, Persistent intercolonial trunkroute-marking in the African weaver ant Oecophylla longinoda: Tom Thumb’s versus Ariadne’s orienting strategies, Ethology 88: 89–98.

13. B Hölldobler, EO Wilson 1978, The multiple recruitment systems of the African weaver ant Oecophylla longinoda, Behav. Ecol. Sociobiol. 3: 19–60.

14. For other examples of ritualized behaviors in ants, see Bert Hölldobler and Edward O. Wilson, The Superorganism (New York: W.W. Norton, 2008).

15. Bert Hölldobler and Edward O. Wilson, Journey to the Ants (Cambridge, MA: Harvard University Press, 1994), p. 43.

16. D Leston 1971, Ants, capsids and swollen-shoot in Ghana: Interactions and the implications for pest control, Proc. 3rd Int. Cocoa Res. Conf. Accra (Ghana) (1969), pp. 205–221.

17. Defense of their termite resources is bolstered by preemptive attacks on competing colonies located closest to these prey: CJ Lumsden, B Hölldobler 1983, Ritualized combat and intercolony communication in ants, J. Theor. Biol. 100: 81–98.

18. Some human pastoralists can be viewed, like honeypot ants, as defending their resources (i.e., animal herds) rather than territorial lands per se; Robert L. Kelly and Michael Rosenberg, personal communication; M Rosenberg 1998, Cheating at musical chairs: Territoriality and sedentism in an evolutionary context, Curr. Anthropol. 39: 653–682.

19. Robert L. O’Connell, Ride of the Second Horseman: The Birth and Death of War (New York: Oxford University Press, 1995), p. 49.

20. B Hölldobler 1983, Territorial behavior in the green tree ant (Oecophylla smaragdina), Biotropica 15: 241–250.

21. L Lefebvre, SM Reader, D Sol 2004, Brains, innovations, and evolution in birds and primates, Brain Behav. Evol. 63: 233–246.

22. RL Carneiro 2000, The transition from quantity to quality: A neglected causal mechanism in accounting for social evolution, Proc. Nat. Acad. Sci. 97: 12926–12931. These novel mechanisms can in turn create further surpluses and increases in population; see Elman R. Service, Origins of the State and Civilization (New York: W.W. Norton, 1975).

23. For ants generally, see, e.g., M Beekman, DJT Sumpter, FLW Ratnieks 2001, Phase transition between disordered and ordered foraging in pharaoh’s ants, Proc. Nat. Acad. Sci. 98: 9703–9706; and R Beckers, S Goss, J-L Deneubourg, JM Pasteels 1989, Colony size, communication, and ant foraging strategy, Psyche 96: 239–256.

24. This estimate is based on a small colony with twelve nests bringing in 45,000 prey per year; see A Dejean 1991, Adaptation d’Oecophylla longinoda aux variations spatio-temporelles de la densité de proies, Entomophaga 36: 29–54.

25. A Dejean, Prey capture strategy of the African weaver ant, in Applied Myrmecology: A World Perspective, ed. RK Vander Meer, K Jaffe, A Cedeno (Boulder, CO: Westwood Press, 1990), pp. 472–481.

26. Dale Peterson and Richard W. Wrangham, Demonic Males: Apes and the Origins of Human Violence (New York: Houghton Mifflin, 1996), pp. 5–21.

27. W Federle, W Baumgartner, B Hölldobler 2004, Biomechanics of ant adhesive pads: Frictional forces are rate-and temperature-dependent, J. Exp. Biol. 207: 67–74.

28. J Wojtusiak, E Godzinska, A Dejean 1995, Capture and retrieval of very large prey by workers of the African weaver ant, Oecopylla longinoda, Trop. Zool. 8: 309–318.

29. N Rastogi 2000, Prey concealment and spatiotemporal patrolling behaviour of the Indian tree ant Oecophylla smaragdin a, Insectes Soc. 47: 92–93.

30. DL Cassill, J Butler, SB Vinson, DE Wheeler 2005, Cooperation during prey digestion between workers and larvae in the ant Pheidole spadonia, Insectes Soc. 52: 339–343.

31. A number of related ants show similar behavior; see C Saux, BL Fisher, GS Spicer 2004, Dracula ant phylogeny as inferred by nuclear 28S rDNA sequences and implications for ant systematics, Mol. Phylogen. Evol. 33: 457–468.

32. K Masuko 1989, Larval hemolymph feeding in the ant Leptanilla japonica by use of a specialized duct organ, the “larval hemolymph tap,” Behav. Ecol. Sociobiol. 24: 127–132.

33. The fastest and most voluminous liquid feeders tend to be nondominant ants (see chapter 10) that grab meals and run; see DW Davidson, SC Cook, RR Snelling 2004, Liquid-feeding performances of ants: Ecological and evolutionary implications, Oecologia 139: 255–266; and DW Davidson 1997, The role of resource imbalances in the evolutionary ecology of tropical arboreal ants, Biol. J. Linn. Soc. 61: 153–181.

34. B Hölldobler 1985, Liquid food transmission and antennation signals in ponerine ants, Isr. J. Entomol. 19: 89–99.

35. See, e.g., Walter R. Tschinkel, The Fire Ants (Cambridge, MA: Harvard University Press, 2006), pp. 332–333.

36. MW Moffett 1985, An Indian ant’s novel method for obtaining water, Natl. Geogr. Res. 1: 146–149.

37. EO Wilson, RW Taylor 1964, A fossil ant colony: New evidence of social antiquity, Psyche 71: 93–103.

38. LU Gadrinab, M Belin 1981, Biology of the green spots in the leaves of some dipterocarps, Malay. For. 44: 253–266.

39. Weaver ants are known to catch and eat the pollinators of one tree species, so the value of their protective services may be mixed (though some flowers may secrete repellants to get around problems with the ants); see K Tsuji, A Hasyim, H Nakamura, K Nakamura 2004, Asian weaver ants, Oecophylla smaragdina, and their repelling of pollinators, Ecol. Res. 19: 669–673; and J Ghazoul 2001, Can floral repellents pre-empt potential ant-plant conflicts?, Ecol. Lett. 4: 295–299.

40. GM Wimp, TG Whitham, Host plants mediate ant-aphid mutualisms and their effects on community structure and diversity, in Ecological Communities: Plant Mediation in Indirect Interaction Webs, ed. T Ohgushi, TP Craig, PW Price (Cambridge: Cambridge University Press, 2007), pp. 683–738.

41. Many taxonomists now call these insects Sternorrhyncha. Before Homoptera excrete sap, they remove a proportion of its amino-nitrogens and convert many of its simple sugars into polysaccharides; such changes are considered minor, however, and the ants that feed on honeydew are therefore widely treated as “primary consumers.”

42. See, e.g., JAH Benzie 1985, Selective positioning of arboreal tents by weaver ants Oecophylla smaragdina: A possible co-evolutionary development with Maha-dan trees, Syzygium cumini, Aust. Entomol. Mag. 12: 17–19. At colony borders, pavilions can serve simultaneously as barrack nests, housing both warriors and Homoptera.

43. JR Malcolm, Insect biomass in Amazonian forest fragments, in Canopy Arthropods, ed. NE Stork, J Adis, RK Didham (London: Chapman & Hall, 1997), pp. 510–533.

44. Deby Cassill, personal communication; D Cassill 2003, Rules of supply and demand regulate recruitment to food in an ant society, Behav. Ecol. Sociobiol. 54: 441–450; and Thomas D. Seeley, The Wisdom of the Hive (Cambridge, Mass.: Harvard University Press, 1995).

45. AA Sorensen, TM Busch, SB Vinson 1985, Control of food influx by temporal subcastes in the fire ant, Solenopsis invicta, Behav. Ecol. Sociobiol. 17: 191–198.

46. The body takes what you give it: only nutrients such as iron and calcium are subject to shifts in absorption based on need (though communication between the gut and brain can help regulate appetite); see OB Chaudhri, V Salem, KG Murphy, SR Bloom 2008, Gastrointestinal satiety signals, Annu. Rev. Physiol. 70: 239–256.

47. Marauder ants and army ants kill Homoptera rather than collect honeydew, though for examples to the contrary, see William H. Gotwald Jr., Army Ants: The Biology of Social Predation (Ithaca, NY: Cornell University Press, 1995). Because nomadic ants are unlikely to return to the same spot, eating the honeydew yields these ants a lower payoff than predation.

10. Fortified Forests

1. Some of my discussion of canopy biology in this chapter is adapted from MW Moffett 2001, Nature and limits of canopy biology, Selbyana 22: 155–179; and Mark W. Moffett, The High Frontier: Exploring the Tropical Rainforest Canopy (Cambridge, MA: Harvard University Press, 1994).

2. DW Yu 1994, The structural role of epiphytes in ant gardens, Biotropica 26: 222–226.

3. At least one of the epiphytes has seeds with a scent attractive to the ants; see E Youngsteadt, S Nojima, C Häberlein, S Schulz, C Schal 2008, Seed odor mediates an obligate ant-plant mutualism in Amazonian rainforests, Proc. Natl. Acad. Sci. 105: 4571–4575.

4. A Vantaux, A Dejean, A Dor, J Orivel 2007, Parasitism versus mutualism in the ant-garden parabiosis between Camponotus femoratus and Crematogaster levior, Insectes Soc. 54: 95–99; and DW Davidson 1988, Ecological studies of neotropical ant gardens, Ecology 69: 1138–1152.

5. The most abundant ant species, measured in numbers of individuals, are among the most successful organisms; see JE Tobin, Ecology and diversity of tropical forest canopy ants, in Forest Canopies, ed. Margaret D. Lowman and Nalini M. Nadkarni (St. Louis, MO: Academic Press, 1995), pp. 129–147. It would be interesting to study the abundance of ant species in terms of numbers of colonies, as it perhaps should be measured.

6. AY Harada, J Adis, The ant fauna of tree canopies in central Amazonia: A first assessment, in Canopy Arthropods, ed. Nigel E. Stork, Joachim Adis, and Raphael K. Didham (London: Chapman & Hall, 1998), pp. 382–400.

7. JE Tobin, Ants as primary consumers: Diet and abundance in the Formicidae, in Nourishment and Evolution in Insect Societies, ed. James H. Hunt and Christine A. Nalepa (Boulder, CO: Westwood Press, 1994), pp. 129–147.

8. The data on the relative abundance and biomass of ants in the ground are scarce and may be skewed by the numbers of minute mites and springtails in the soil; but see EJ Fittkau, H Klinge 1973, On biomass and trophic structure of the central Amazonian rain forest ecosystem, Biotropica 5: 2–14. Many ground-dwelling species depend on nectaries or Homoptera residing on shrubs, herbs, and the roots of larger plants.

9. This shift in diet occurred several thousand years prior to agriculture (see chapter 15). Of course, both weaver ant colonies and humans in similarly entrenched settlements catch large prey when they can; see, e.g., B Hayden 1990, Nimrods, piscators, pluckers, and planters: The emergence of food production, J. Anthropol. Archaeol. 9: 31–69.

10. A few other species may on occasion come close to engaging in warfare. Honeybees attack weak colonies to steal honey (Tom Seeley, personal communication). Researchers have observed piles of dead nasute termites, suggesting recent battles involving mostly the worker caste, and hundreds of workers will respond en masse to kill even a single conspecific (James Traniello, personal communication; SC Levings, ES Adams 1984, Intra- and interspecific territoriality in Nasutitermes in a Panamanian mangrove forest, J. Anim. Ecol. 53: 705– 714; BL Thorne 1982, Termite-termite interactions: Workers as an agnostic caste, Psyche 89: 133–150). However, workers in some termite species that live in huge colonies mix freely without aggression (Scott Turner, personal communication). Male chimpanzees are known to conduct predatory raids to kill neighboring chimpanzees, usually one at a time, which if repeated can devastate adjacent communities (as is often the case for small human bands; see note 30); see Jane Goodall, The Chimpanzees of Gombe (Cambridge, MA: Harvard University Press, 1986).

11. JT Longino, NM Nadkarni 1990, A comparison of ground and canopy leaf litter ants in a neotropical montane forest, Psyche 97: 81–93.

12. SKA Robson, RJ Kohout 2005, Evolution of nest-weaving behaviour in arboreal nesting ants of the genus Polyrhachis, Aust. J. Entomol. 44: 164–169; BL Fisher, HG Robertson 1999, Silk production by adult workers of the ant Melissotarsus emeryi in South African fynbos, Insectes Soc. 46: 78–83.

13. Victor Rico-Gray and Paulo S. Oliveira, The Ecology and Evolution of Ant-Plant Interactions (Chicago: University of Chicago Press, 2007).

14. HT Huang, P Yang 1987, The ancient cultured citrus ant, BioScience 37: 665–671; P Van Mele 2008, A historical review of research on the weaver ant Oecophylla in biological control, Agr. For. Entomol. 10: 13–22.

15. J. Offenberg, MG Nielsen, DJ Macintosh, S Havanon, S Aksornkoae 2004, Evidence that insect herbivores are deterred by ant pheromones, Proc. R. Soc. Lond. Ser. B 271: S433–S435.

16. SH Wittwer, FG Teubner 1959, Foliar absorption of mineral nutrients, Annu. Rev. Plant Physiol. 10: 13–30.

17. J Offenberg, MG Nielsen, DJ Macintosh, S Aksornkoae, S Havanon 2006, Weaver ants increase premature loss of leaves used for nest construction in Rhizophora trees, Biotropica 38: 782–785.

18. Gina Wimp, personal communication; GM Wimp, TG Whitham 2001, Biodiversity consequences of predation and host plant hybridization on an aphidant mutualism, Ecology 82: 440–452.

19. A difficulty for this idea is that Homoptera tend to represent a bigger drain on a plant than do nectaries; see, e.g., F Ito, S Higashi 1991, An indirect mutualism between oaks and wood ants via aphids, J. Anim. Ecol. 60: 463–470. The opposite hypothesis, that nectaries evolved to distract ants from tending harmful insects, therefore seems unlikely; see JXI Becerra, DL Venable 1989, Extrafloral nectaries: A defense against ant-Homoptera mutualisms?, Oikos 55: 276–280.

20. N Blüthgen, K Fiedler 2002, Interactions between weaver ants Oecophylla smaragdina, homopterans, trees, and lianas in an Australian rain forest canopy, J. Anim. Ecol. 71: 793–801.

21. C Djieto-Lordon, A Dejean 1999, Tropical arboreal ant mosaics: Innate attraction and imprinting determine nest site selection in dominant ants, Behav. Ecol. Sociobiol. 45: 219–225.

22. In one study, trees without Oecophylla grew faster, which the authors attribute to “overcompensation”; i.e., the trees invested more in growth when under attack by herbivores: J Offenberg, MG Nielsen, DJ Macintosh, S Havanon, S Aksornkoae 2005, Lack of ant attendance may induce compensatory plant growth, Oikos 111: 170–178.

23. TH Jones, DA Clark, AA Edwards, DW Davidson, TF Spande, RR Snelling 2004, The chemistry of exploding ants, Camponotus spp. (cylindricus complex), J. Chem. Ecol. 30: 1479–1492.

24. A Tofilski, MJ Couvillon, SEF Evison, H Helanterä, EJH Robinson, FLW Ratnieks 2008, Preemptive defensive self-sacrifice by ant workers, Am. Nat. 172: E239–E243.

25. LMA Bettencourt, J Lobo, D Helbing, C Kühnert, GB West 2007, Growth, innovation, scaling, and the pace of life in cities, Proc. Natl. Acad. Sci. 104: 7301–7306.

26. Thanks to Bob Jeanne and Anna Dornhaus for discussions on this issue, which was first addressed by CD Michener 1964, Reproductive efficiency in relation to colony size in hymenopterous societies, Insectes Soc. 11: 317–341.

27. Can a large colony bounce back from a conflict more easily because it will have enough survivors to take over the important functions previously handled by its lost members or because its population will rebound faster through more prolific reproduction? Neither idea is completely credible. A loss of 100,000 workers in a colony of 1,000,000 could make all the difference if that colony then has to spar with neighbors that are also a million strong, whereas even modest losses can be devastating in the long term to small human bands that face conflict frequently. See Lawrence H. Keeley, War before Civilization: The Myth of the Peaceful Savage (New York: Oxford University Press, 1996).

28. DW Davidson, J-P Lessard, CR Bernau, SC Cook 2007, The tropical ant mosaic in a primary Bornean rain forest, Biotropica 39: 468–475.

29. See figure 4-3 in A Buschinger, U Maschwitz, Defensive behavior and defensive mechanisms in ants, in Defensive Mechanisms in Social Insects, ed. Henry R. Hermann (New York: Praeger Scientific, 1984), pp. 95–150.

30. Fights between human hunter-gatherer bands are often personal campaigns that usually result in isolated deaths in stealthy, relatively low-risk raids in which all participants have something to gain—the kind of attack conducted by chimpanzees as well. Repeated raids could add up to heavy mortality and the extinction of entire bands in times of scarcity, but pitched battles and massacres, which are typically perilous and based on sacrifice for the society rather than direct self-interest, are the exception. See DT Campbell 1975, On the conflicts between biological and social evolution and between psychology and moral tradition, Am. Psychol. 30: 1103–1126. Internal division of human societies into hierarchies and subgroupings, which tends to go hand in hand with population growth, may also be the primary driver of warfare; see Raymond C. Kelly, Warless Societies and the Origin of War (Ann Arbor: University of Michigan Press, 2000).

31. See, e.g., N Blüthgen, K Fiedler 2004, Competition for composition: Lessons from nectar-feeding ant communities, Ecology 85: 1479–1485.

32. A Dejean, B Corbara, J Orivel, M Leponce 2007, Rainforest canopy ants: The implications of territoriality and predatory behavior, Func. Ecosyst. Commu. 1: 105–120.

33. DA Jackson 1984, Ant distribution patterns in a Cameroonian cocoa plantation: Investigation of the ant mosaic hypothesis, Oecologia 62: 318–324. For rules of engagement between ant colonies, see NR Franks, LW Partridge 1993, Lanchester battles and the evolution of combat in ants, Anim. Behav. 45: 197–199.

34. Pruning attached plants and patrolling for herbivores may occur in an exaggerated (and more tightly targeted) manner in ants involved in ant-plant relationships as compared to ant species with a looser association with resident trees, such as Oecophylla, but potentially mutualistic advantages could apply to both. See DW Davidson, JT Longino, RR Snelling 1988, Pruning of host plant neighbors by ants: An experimental approach, Ecology 69: 801–808.

35. ME Frederickson, MJ Greene, DM Gordon 2005, “Devil’s gardens” bedevilled by ants, Nature 437: 495–496.

36. Some have attacked the idea that mosaics exist, which is strange to those of us who climb into the trees to observe the distribution of ants in them firsthand. For a review of concepts and controversies, see N Blüthgen, NE Stork 2007, Ant mosaics in a tropical rainforest in Australia and elsewhere: A critical review, Aust. Ecol. 32: 93–104.

37. For example, see NJ Sanders, GM Crutsinger, RR Dunn, JD Majer, JHC Delabie 2007, An ant mosaic revisited: Dominant ant species disassemble arboreal ant communities but co-occur randomly, Biotropica 39: 422–427.

38. This issue and many ideas around it are pursued in SP Yanoviak, M Kaspari 2000, Community structure and the habitat templet: Ants in the tropical forest canopy and litter, Oikos 89: 259–266.

39. Army ants ascend trees on occasion but have greater effects on the ground; see M Kaspari, S O’Donnell 2003, High rates of army ant raids in the neotropics and implications for ant colony and community structure, Evol. Ecol. Res. 5: 933–939.

40. D Leston 1970, Entomology of the cocoa farm, Annu. Rev. Entomol. 15: 273–294.

41. The dynamics are similar to the community shifts that occur when gaps open up in the forest when trees die (see chapter 14). See Andrew F. G. Bourke and Nigel R. Franks, Social Evolution in Ants (Princeton: Princeton University Press, 1995); JD Majer 1976, The maintenance of the ant mosaic in Ghana cocoa farms, J. Appl. Ecol. 13: 123–144; and JD Majer 1976, The influence of ants and ant manipulation on the cocoa farm fauna, J. Appl. Ecol. 13: 157–175.

42. PJ Folgarait 1998, Ant biodiversity and its relationship to ecosystem functioning: A review, Biodivers. Conserv. 7: 1221–1244.

43. For examples, see A Floren, A Biun, KE Linsenmair 2002, Arboreal ants as key predators in tropical lowland rainforest trees, Oecologia 131: 137–144.

44. Terry Erwin, personal communication; TL Erwin, The biodiversity question. How many species of terrestrial arthropods are there?, in Forest Canopies, 2d ed., ed. Margaret D. Lowman and H. Bruce Rinker (St. Louis, Mo.: Academic Press, 2004), pp. 259–269.

45. Y Haila 1990, Toward an ecological definition of an island: A northwest European perspective, J. Biogeogr. 17: 561–568; DH Janzen 1973, Host plants as islands. II. Competition in evolutionary and contemporary time, Am. Nat. 107: 786–790.

46. Robert H. MacArthur and Edward O. Wilson, The Theory of Island Biogeography (Princeton: Princeton University Press, 1967). I explore the idea of “patchwork biogeography” in MW Moffett 2001, The nature and limits of canopy biology, Selbyana 22: 155–179.

11. Negotiating the Physical World

1. Such height-based differentiation is called stratification, which is broadly defined as “any nonuniform vertical distribution within vegetation”; see MW Moffett 2000, What’s “up”? A critical look at basic terms of canopy biology, Biotropica 32: 569–596.

2. CA Brühl, G Gunsalam, KE Linsenmair 1998, Stratification of ants in a primary rain forest in Sabah, Borneo, J. Trop. Ecol. 14: 285–297. Subterranean ants stratify as well; see KT Ryder-Wilkie, AL Mertl, JFA Traniello 2007, Biodiversity below ground: Probing the subterranean ant fauna of Amazonia, Naturwissenschaften 94: 725–731.

3. Herbicides simplify but do not eliminate this hidden lawn structure. SH Roxburgh, AJ Watkins, JB Wilson 1993, Lawns have vertical stratification, J. Veg. Sci. 4: 699–704. For a description of the universality of strata in communities, see MW Moffett 2001, The nature and limits of canopy biology, Selbyana 22: 155–179.

4. A Lipp, H Wolf, F-O Lehmann 2005, Walking on inclines: Energetics of locomotion in the ant Camponotus, J. Exp. Biol. 208: 707–719.

5. John B. S. Haldane, Possible Worlds, and Other Papers (London: Harper & Brothers, 1928); see also Steven Vogel, Life’s Devices: The Physical World of Animals and Plants (Princeton: Princeton University Press, 1988).

6. SP Yanoviak, M Kaspari 2000, Community structure and the habitat templet: Ants in the tropical forest canopy and litter, Oikos 89: 259–266.

7. PD Haemig 1997, Effects of birds on the intensity of ant rain: A terrestrial form of invertebrate drift, Anim. Beh. 54: 89–97; and B Hölldobler 1965, Springende Ameisen, Mitt. Schweiz. entomol. Ges. 30: 80–81.

8. SP Yanoviak, R Dudley, M Kaspari 2005, Directed aerial descent in canopy ants, Nature 433: 624–626.

9. For details, see R Dudley, G Byrnes, SP Yanoviak, B Borrell, R Brown, J McGuire 2007, Gliding and the functional origins of flight: Biomechanical novelty or necessity? Annu. Rev. Ecol. Syst. 38: 179–201.

10. Eberhard Horn, Gravity, in Comprehensive Insect Physiology, Biochemistry, and Pharmacology, vol. 6, ed. Gerald A. Kerkut and Lawrence I. Gilbert (Oxford: Pergamon, 1985), pp. 557–576; and Hubert Markl 1974, Perception of gravity and of angular acceleration in invertebrates, in Handbook of Sensory Physiology, vol. 6/1, ed. Hans H. Kornhuber (Heidelberg: Springer Verlag, 1974), pp. 17–74. Even ants dwelling in a relatively flat desert environment can be trained to climb specific distances, though they tend to overshoot the correct height; see G Grah, R Wehner, B Ronacher 2007, Desert ants do not acquire and use a three-dimensional global vector, Front. Zool. 4: 12; and G Grah, R Wehner, B Ronacher 2005, Path integration in a three-dimensional maze: Ground distance estimation keeps desert ants Cataglyphis fortis on course, J Exp. Biol. 208: 4005–4011.

11. Francis Hallé, Roelof A. A. Oldeman, and P. Barry Tomlinson, Tropical Trees and Forests: An Architectural Analysis (New York: Springer-Verlag, 1978).

12. Crestline orientation is untested in windblown conditions when the gravity vector would be difficult for ants to measure; see JH Klotz, BL Reid 1992, The use of spatial cues for structural guideline orientation in Tapinoma sessile and Camponotus pennsylvanicus, J. Insect Behav. 5: 71–82; R. Jander 1990, Arboreal search in ants: Search on branches, J. Insect Behav. 3: 515–527; and JH Klotz, SL Cole, HR Kuhns 1985, Crest-line orientation in Camponotus pennsylvanicus, Insectes Soc. 32: 305–312. One temperate ant shows a more random leaf and branch search pattern; see RM Weseloh 2001, Patterns of foraging of the forest ant Formica neogagates on tree branches, Biol. Control 20: 16–22. Ants use similar rules to navigate low-growing plants; see KN Ganeshaiah, T Veena 1988, Plant design and non-random foraging by ants on Croton bonplandianum, Anim. Behav. 36: 1683–1690.

13. CJ Kleineidam, M Ruchty, ZA Casero-Montes, F Roces 2007, Thermal radiation as a learned orientation cue in leaf-cutting ants (Atta vollenweideri), J. Insect Phys. 53: 478–487.

14. R Jander, U Jander 1998, The light and magnetic compass of the weaver ant, Oecophylla smaragdina, Ethology 104: 743–758.

15. B Hölldobler 1980, Canopy orientation: A new kind of orientation in ants, Science 210: 86–88.

16. B Hölldobler 1983, Territorial behavior in the green tree ant (Oecophylla smaragdina), Biotropica 15: 241–250.

17. MD Breed, JM Harrison 1987, Individually discriminable recruitment trails in a ponerine ant, Insectes Soc. 34: 222–226.

18. AP Baader 1996, The significance of visual landmarks for navigation of the giant tropical ant, Paraponera clavata, Insectes Soc. 43: 435–450. Navigating ants can identify the same object from different angles; see SPD Judd, TS Collett 1998, Multiple stored views and landmark guidance in ants, Nature 392: 710–714.

19. JF Harrison, JH Fewell, TM Stiller, MD Breed 1988, Effects of experience on use of orientation cues in the giant tropical ant, Anim. Behav. 37: 869–871.

20. A Lioni, C Sauwens, G Theraulaz, J-L Deneubourg 2001, Chain formation in Oecophylla longinoda, J. Insect Behav. 14: 679–696.

21. U Maschwitz, J Moog 2000, Communal peeing: A new mode of flood control in ants, Naturwissenschaften 87: 563–565.

22. J Moog, T Drude, U Maschwitz, D Agosti 1997, Flood control by ants: Water-bailing behaviour in the Southeast Asian plant-ant genus Cladomyrma, Naturwissenschaften 84: 242–245; and RW Klein, U Maschwitz, D Kovac 1993, Flood control by ants: A South-East Asian bamboo-dwelling Tetraponera bails water from its internode nests, Insectes Soc. 40: 115–118.

23. Carton can also be waterproof because the surface tension of water transforms its porous surface into a complete shield, though buffeting by rain and wind can cause breakage. Thus many carton-nesting species are restricted to the understory, with antgarden ants (chapter 10) shielding their nest beneath garden foliage.

24. N Rastogi 2004, Behavioral strategy of returning foragers of the arboreal ant Oecophylla smaragdina during the monsoon, J. Bombay Nat. Hist. Soc. 101: 388–391.

25. Deby Cassill, personal communication, and WL Morrill 1974, Dispersal of red imported fire ants by water, Fla. Entomol. 57: 38–42.

26. Joachim Adis, Herbert O.R. Schubart 1984, Ecological research on arthropods in central Amazonian forest ecosystems with recommendations for study procedures, in Trends in Ecological Research for the 1980s, ed. June H. Cooley and Frank B. Golley (New York: Plenum Press, 1984), pp. 111–144.

27. Michael Goulding, Amazon: The Flooded Forest (New York: Sterling, 1990), pp. 26–27.

28. J Adis 1982, Eco-entomological observations from the Amazon, III: How do leafcutting ants of inundation forests survive flooding? Acta Amazon. 12: 839–840.

29. Information on both carpenter ants is from MB DuBois, R Jander 1985, Leg coordination and swimming in an ant, Camponotus americanus, Physiol. Entomol. 10: 267–270.

30. Simon Robson, personal communication, and MG Nielsen, Nesting biology of the mangrove mudnesting ant Polyrhachis sokolova in northern Australia, Insectes Soc. 44 (1997): 15–21.

31. CM Clarke, RL Kitching 1995, Swimming ants and pitcher plants: A unique ant-plant interaction from Borneo, J. Trop. Ecol. 11: 589–602.

32. HF Bohn, W Federle 2004, Insect aquaplaning: Nepenthes pitcher plants capture prey with the peristome, a fully wettable water-lubricated anisotropic surface, Proc. Natl. Acad. Sci. 101: 14138– 14143.

33. MW Moffett 1989, Notes on the behavior of the dimorphic ant Oligomyrmex overbecki, Psyche 93: 107–116.

34. First proposed for animals in B Rensch 1956, Increase in learning with increase in brain size, Am. Nat. 90: 81–95; for ants, see BL Cole 1985, Size and behavior in ants: Constraints on complexity, Proc. Natl. Acad. Sci. 82: 8548–8551. I doubt that idea applies to most polymorphic species, in which majors tend to be limited in their repertoires. For other intriguing ideas about the relation between colony size, worker size, and productivity, see M Kaspari 2005, Global energy gradients and size in colonial organisms: Worker mass and worker number in ant colonies, Proc. Natl. Acad. Sci. 102: 5079–5083.

35. A baleen whale’s trawling may most closely resemble foraging by army ants, except army ants raid together to catch prey larger than they could individually, whereas whales trawl to catch prey smaller than normal for an animal of their size. Trawling behavior can be very effective for large individuals, and both army ant colonies and whales have evolved to become larger over time. Ironically, the terrestrial vertebrate with the closest equivalent to this behavior may be the anteater; in general, the effectiveness of trawling for a land vertebrate is reduced by the intake of detritus (Brian McNab, personal communication).

36. At a smaller scale, superabundant mites consume plant pests too minute for ants and live in microscopic protective retreats provided by the plants; see GQ Romero, WW Benson 2005, Biotic interactions of mites, plants, and leaf domatia, Curr. Opin. Plant Biol. 8: 436–440; and DE Walter, Hidden in plain sight: Mites in the canopy, in Forest Canopies, 2d ed., ed. Margaret D. Lowman and H. Bruce Rinker (St. Louis, Mo.: Academic Press, 2004), pp. 224–241.

37. Technically, workers operate in “series parallel”; see George F. Oster and Edward O. Wilson, Caste and Ecology in the Social Insects (Princeton: Princeton University Press, 1978), pp. 12–14.

38. These systems of control are probably necessary to manage unions of self-interested, often distantly related humans who mostly don’t know each other; see Stephen K. Sanderson, ed., Social Transformations: A General Theory of Historical Development, expanded ed. (Oxford: Blackwell, 1995).

39. Raphael D. Sagarin and Terence Taylor, eds., Natural Security: A Darwinian Approach to a Dangerous World (Berkeley: University of California Press, 2008).

40. One World Bank official seeking solutions to global problems has proposed that hierarchical governments be replaced by networked governance; see J-F Rischard, Global issues networks: Desperate times deserve innovative measures, Washington Quarterly 26 (2002): 17–33.

41. A few ants (most of them with small colonies) survive the queen’s death by having the workers take over reproduction; see the conclusion to this book and Bert Hölldobler and Edward O. Wilson, The Superorganism (New York: W.W. Norton, 2008), pp. 356–426.

42. A Buschinger, U Maschwitz, Defensive behavior and defensive mechanisms in ants, in Defensive Mechanisms in Social Insects, ed. Henry R. Hermann (New York: Praeger Scientific, 1984), pp. 95–150; the quote appears on p. 124.

12. Slaves of Sagehen Creek

1. I focus here on breviceps, but there is excellent work on the other Polyergus species.

2. Donato Grasso, personal communication. Another fascinating possibility is that the Formica bring up some brood to make them accessible to raiding parties in a tactic that diverts the Polyergus from more critical parts of the nest, in a kind of “lizard loses its tail” sacrifice.

3. Apparently colony identity odors can be detected not just at contact but also over distances of a few millimeters; see AS Brandstaetter, A Endler, CJ Kleineidam 2008, Nestmate recognition in ants is possible without tactile interaction, Naturwissenschaften 95: 601–608.

4. Propaganda substances have so far been studied only in the European Amazon ant; see R. Visicchio, A Mori, DA Grasso, C Castracani, F Le Moli 2001. Glandular sources of recruitment, trail, and propaganda semiochemicals in the slave-making ant Polyergus rufescens, Ethol. Ecol. Evol. 13: 361–372.

5. Those Formica species that have a shorter history of conflict with the Amazons tend to fight back more, and as a consequence they suffer higher mortality from raids. The species raided can vary from place to place, even from colony to colony; see, e.g., JM Bono, R Blatrix, MF Antolin, JM Herbers 2007, Pirate ants (Polyergus breviceps) and sympatric hosts (Formica occulta and Formica sp. cf. argentea): Host specificity and coevolutionary dynamics, Biol. J. Linn. Soc. 91: 565–572.

6. JM Herbers, S Foitzik 2002, The ecology of slavemaking ants and their hosts in north temperate forests, Ecology 83: 148–163; and RJ Stuart 1988, Collective cues as a basis for nestmate recognition in polygynous leptothoracine ants, Proc. Natl. Acad. Sci. 85: 4572–4575.

7. TO Richardson, PA Sleeman, JM McNamara, AL Houston, NR Franks 2007, Teaching with evaluation in ants, Curr. Biol. 17: 1520–1526; and E. Leadbeater, N Raine, L Chittka 2006, Social learning: Ants and the meaning of teaching, Curr. Biol. 16: R323–R325.

8. RJ Stuart 1986, An early record of tandem running in leptothoracine ants: Gottfrid Adlerz 1896, Psyche 93: 103–106; and TM Alloway 1979, Raiding behaviour of two species of slave-making ants, Harpagoxenus americanus and Leptothorax duloticus, Anim. Behav. 27: 202–210.

9. J Beibl, RJ Stuart, J Heinze, S Foitzik 2005, Six origins of slavery in formicoxenine ants, Insectes Soc. 52: 291–297.

10. MW Moffett 1989, Life in a nutshell, National Geographic 175: 783–796.

11. A Lenoir, P D’Ettorre, C Errard 2001, Chemical ecology and social parasitism in ants, Annu. Rev. Entomol. 46: 573–599. Slavemaker colonies act more like predators than parasites, which feed on a single host; see M Brandt, S Foitzik, B Fischer-Blass, J Heinze 2005, The coevolutionary dynamics of obligate ant social parasite systems: Between prudence and antagonism, Biol. Rev. Camb. Philos. Soc. 80: 251–267. We’ll see in the next chapter that the Amazons collect some of the colony’s food, in that the slaves eat some of the raided brood.

12. John Lubbock, Ants, Bees, and Wasps (New York: Appleton, 1883). Thief ants belong to Solenopsis subgenus Diplorhoptrum.

13. Pierre Huber, Recherches sur les moeurs des fourmis indigènes (Geneva: J. J. Paschoud, 1810), pp. 219–224.

14. Charles Darwin, Origin of Species (London: John Murray, 1859), pp. 219–224.

15. Milton Meltzer, Slavery: A World History (Chicago: Da Capo Press, 1993); and Orlando Patterson, Slavery and Social Death: A Comparative Study (Cambridge, MA: Harvard University Press, 1982).

16. A Achenbach, S Foitzik 2009, First evidence for slave rebellion: Enslaved ant workers systematically kill the brood of their social parasite Protomognathus americanus, Evolution 63: 1068–1075.

17. W Czechowski 2006, Route of Formica polyctena as a factor promoting emancipation of Formica fusca slaves from colonies of Polyergus rufescens, Pol. J. Ecol. 54: 159–162.

18. Some fleeting tussles between slaves and slavemakers have also been recorded, most prevalently in species in the early stages of the evolution of slavemaking; see Bert Hölldobler and Edward O. Wilson, The Ants (Cambridge, MA: Harvard University Press, 1990), p. 463; and EO Wilson 1975, Leptothorax duloticus and the beginnings of slavery in ants, Evolution 29: 108–119.

19. Karl Marx’s idea of false consciousness was given its name by Friedrich Engels; see György Lukács, History and Class Consciousness: Studies in Marxist Dialectics (Cambridge, MA: MIT Press, 1971).

20. Even the adult workers may shift over from a losing colony; see GB Pollock, SW Rissing 1989, Intraspecific brood raiding, territoriality, and slavery in ants, Am. Nat. 133: 61–70.

21. For similar reasons, the myth of Tarzan, raised by apes, is more plausible than that of Romulus and Remus, the legendary wolf-raised founders of Rome. A stunning exception for the ants is a parasitic species that never rears its own brood but rather sneaks it into the nurseries of a distantly related species; see U Maschwitz, C Go, E Kaufmann, A Buschinger 2004, A unique strategy of host colony exploitation in a parasitic ant: Workers of Polyrhachis lama rear their brood in neighbouring host nests, Naturwissenschaften 91: 40–43. Should employing a related species for labor be called slavery? In Planet of the Apes, at least, we accept that apes have turned humans into “slaves” without the word sounding a false note.

22. M Stoneking 2003, Widespread prehistoric human cannibalism: Easier to swallow, Trends Ecol. Evol. 18: 489–490.

23. Thanks to Sarah Hrdy for examples. One author proposes that kidnapping by primates is “ancestral” to slavery among humans, a view I have trouble believing: “Surrounded by strangers I thought were my friends,” Ethology 113: 499–510.

24. These birds do not imprint on their parents and therefore will follow whatever authority figure gives the right signal; see RG Heinsohn 1991, Kidnapping and reciprocity in cooperatively breeding white-winged choughs, Anim. Behav. 41: 1097–1100.

25. R Blatrix, JM Herbers 2003, Coevolution between slave-making ants and their hosts: Host specificity and geographic variation, Mol. Ecol. 12: 2809–2816.

26. JM Herbers 2006, The loaded language of science, Chron. High. Educ. 52: B5. A technical alternative is the term dulosis, derived from the Greek word for slave.

27. H Topoff, Slave-making queens, Scientific American 281: 84–90.

28. Chris Boehm, Hierarchy in the Forest (Cambridge, MA: Harvard University Press, 1999); and Robert L. O’Connell, Ride the Second Horseman: The Birth and Death of War (New York: Oxford University Press, 1995).

29. Bert Hölldobler and Edward O. Wilson, Journey to the Ants (Cambridge, MA: Harvard University Press, 1994), p. 9.

30. Frans de Waal, Good Natured: The Origins of Right and Wrong in Humans and Other Animals (Cambridge, MA: Harvard University Press, 1997).

31. This section summarizes Topoff, Slave-making queens, cited in n. 27.

32. DA Grasso, A Mori, F Le Moli, J Billen 2005, Morpho-functional comparison of the Dufour gland in the female castes of the Amazon ant Polyergus rufescens, Zoomorphology 124: 149–153.

33. Topoff, Slave-making queens, p. 87, cited in n. 27.

34. It is conceivable that the queen plays a primary role in determining the odor used to signal colony identity in these ants, as has been shown with the related carpenter ants; see NF Carlin, B Hölldobler 1983, Nestmate and kin recognition in interspecific mixed colonies of ants, Science 222: 1027–1029. See also H Topoff, E Zimmerli 1993, Colony takeover by a socially parasitic ant, Polyergus breviceps: The role of chemicals obtained during host-queen killing, Anim. Behav. 46: 479–486.

35. A Buschinger 1986, Evolution of social parasitism in ants, Trends Ecol. Evol. 1: 155–160.

13. Abduction in the Afternoon

1. DA Grasso, A Mori, P D’Ettorre, F Le Moli 1994, Intraspecific raids and territoriality in Polyergus rufescens, Ethol. Ecol. Evol. 3: 81–87; and H Topoff, B LaMon, L Goodloe, M Goldstein 1984, Social and orientation behavior of Polyergus breviceps during slave-making raids, Behav. Ecol. Sociobiol. 15: 273–279.

2. William H. McNeill, The Pursuit of Power: Technology, Armed Force, and Society since A.D. 1000 (Chicago: University of Chicago Press, 1982), p. 131.

3. Dan Stahler, personal communication; Scott Creel and Nancy Marushka Creel, The African Wild Dog: Behavior, Ecology, and Conservation (Princeton: Princeton University Press, 2002), p. 76.

4. H Topoff, D Bodoni, P Sherman, L Goodloe 1987, The role of scouting in slave raids by Polyergus breviceps, Psyche 94: 261–270.

5. See, e.g., J Dobrza´nska, J Dobrza´nski 1989, Controversies on the subject of slave-raids in Amazon ants (genus Polyergus), Acta Neurobiol. Exp. 49: 367–379.

6. See, e.g., E Janssen, B Hölldobler, HJ Bestmann 1999, A trail pheromone component of the African stink ant, Pachycondyla (Paltothyreus) tarsata, Chemoecology 9: 9–11.

7. Free-living Formica ants separate their foraging behavior into similar phases of linear travel and irregular searching, which suggests this strategy has ancient roots; see JFA Traniello, V Fourcassié, TP Graham 1991, Search behavior and foraging ecology of the ant Formica schaufussi: Colony-level and individual patterns, Ethol. Ecol. Evol. 3: 35–47.

8. In fact, the chemical trail of a successful raid lasts long enough for the Amazons to reuse it during the next day or two, if a raid is very productive. It is unknown whether a scout is required for these subsequent raids.

9. EO Wilson 1975, Slavery in ants, Sci. Am. 232: 32–36. According to one interpretation, the Amazon ants continue this tradition of territorial warfare: if Amazons identified their Formica slaves as nestmates, they would raid Formica colonies as if they were attacking their own species: H Topoff 1990, The evolution of slave-making behavior in the parasitic ant genus Polyergus, Ethol. Ecol. Evol. 2: 284–287.

10. Part of the reason for the absence of slavery among army ants is that few of their species attack other army ants, which means that successfully rearing slaves, which are typically close relatives (see chapter 12), from prey booty is unlikely.

11. Their proclivity for territorial battle may explain how it is that enslaved workers of these species sometimes join their masters on slave raids.

12. For a general discussion of tactical deception, see RW Byrne, N Corp 2004, Neocortex size predicts deception rate in primates, Proc. R. Soc. Lond. B 271: 1693–1699. In another example of tactical deception, honeypot ants that find termite prey will instigate tournaments near competing nests to distract their rivals; see B Hölldobler 1981, Foraging and spatiotemporal territories in the honey ant Myrmecocystus mimicus, Behav. Ecol. Sociobiol. 9: 301–314. Bert Hölldobler informs me that genetic studies show slaves taken after such tournaments are common. Honeypot ants were first introduced in chapter 4 in a discussion of how the combatants determine if they are outnumbered.

13. E Cool-Kwait, H Topoff 1984, Raid organization and behavioral development in the slave-making ant Polyergus lucidus, Insectes Soc. 31: 361–374.

14. H Topoff 1985, Effect of overfeeding on raiding behavior in the western slave-making ant Polyergus breviceps, Natl. Geogr. Res. 1: 437–441.

15. RJ Stuart, MW Moffett 1994, Recruitment communication and pheromone trails in the neotropical ants Leptothorax (Nesomyrmex) spininodis and L. (N.) echinatinodis, Experientia 50: 850–852.

16. This hypothesis as well as the importance of a seasonal brood cycle are reviewed by Bert Hölldobler and Edward O. Wilson, The Ants (Cambridge, MA: Harvard University Press, 1990), p. 447.

17. As we saw for the capacity of ants to delay eating in order to group-transport food to a nest (chapter 5), such forbearance is rare among animals generally; see JR Stevens, DW Stephens 2008, Patience, Curr. Biol. 18: R11–R12.

18. See Stephen B. Vander Wall, Food Hoarding in Animals (Chicago: University of Chicago Press, 1990), p. 64. This advantage for slavery in temperate ants could exist even though ants generally do better than solitary insects in hunkering down in their nests to wait out hard times.

19. M Kaspari, L Alonso, S O’Donnell 2000, Three energy variables predict ant abundance at a geographical scale, Proc. R. Soc. Lond. B 267: 485–489.

14. A Fungus Farmer’s Life

1. In this book I do not distinguish leafcutter species unless there are known differences between them. For a general review, see Rainer Wirth, Hubert Herz, Ronald J. Ryel, Wolfram Beyschlag, and Bert Hölldobler, Herbivory of Leaf-Cutting Ants: A Case Study on Atta colombica in the Tropical Rainforest of Panama (Berlin: Springer-Verlag, 2003).

2. Leafcutter workers of all sizes respond to disturbances in the nest, but the largest, the “soldiers,” are particularly effective at repelling vertebrates.

3. SEF Evison, FLW Ratnieks 2007, New role for majors in Atta leafcutter ants, Ecol. Entomol. 32: 451–454. Occasionally the majors (soldiers) help clear trails as well.

4. MW Moffett 1986, Observations of Lophomyrmex ants from Kalimantan, Java, and Malaysia, Malay. Nat. J. 39: 207–211.

5. F Roces, JRB Lighten 1995, Larger bites of leaf-cutting ants, Nature 373: 392–393.

6. AJ Edwards, JD Fawke, JG McClements, SA Smith, P Wyeth 1993, Correlation of zinc distribution and enhanced hardness in the mandibular cuticle of the leaf-cutting ant Atta sexdens rubropilosa, Cell Biol. Int. 17: 697–698.

7. See, e.g., JM van Breda, DJ Stradling 1994, Mechanisms affecting load size determination in Atta cephalotes, Insectes Soc. 41: 423–434.

8. James K. Wetterer, unpublished manuscript.

9. There is some evidence that leafcutter ants are unable to cooperate in carrying any object, no matter what its shape; see JJ Howard 2001, Costs of trail construction and maintenance in the leaf-cutting ant Atta columbica, Behav. Ecol. Sociobiol. 49: 348–356.

10. Still, larger ants have relatively shorter legs and cut fragments small for their size; see JK Wetterer 1995, Forager polymorphism and foraging ecology in the leaf-cutting ant, Atta colombica, Psyche 102: 131–145; and JK Wetterer 1991, Allometry and the geometry of leaf-cutting in Atta cephalotes, Behav. Ecol. Sociobiol. 29: 347–351.

11. M Burd, JJ Howard 2005, Global optimization from suboptimal parts: Foraging sensu lato by leaf-cutting ants, Behav. Ecol. Sociobiol. 59: 234–242.

12. OT Lewis, MM Martin, TJ Czaczkes 2008, Effects of trail gradient on leaf tissue transport and load size selection in leaf-cutter ants, Behav. Ecol. 19: 805–809.

13. RJ Quinlan, JM Cherrett 1979, The role of fungus in the diet of the leaf-cutting ant Atta cephalotes, Ecol. Entomol. 4: 151–160.

14. Michael M. Martin, Invertebrate-Microbial Interactions: Ingested Fungal Enzymes in Arthropod Biology (Ithaca, N.Y.: Comstock Publishing Associates, 1987), pp. 107–124.

15. PF Dowd 1992, Insect fungal symbionts: A promising source of detoxifying enzymes, J. Ind. Microbiol. Biotech. 9: 149–161.

16. AB Abril, EH Bucher 2004, Nutritional sources of the fungus cultured by leaf-cutting ants, Appl. Soil Ecol. 26: 243–247.

17. All termites have microbes in their gut to digest cellulose in wood and dried leaves, but Africa’s fungus-growing termites take this process a step further. Their colonies are basically cows within cows. Workers eat the plant matter, then use their feces to create gardens that look surprisingly like the ones leafcutters construct from foliage. The fungi the termite workers eat pass through their digestive systems intact and do not themselves serve as food. Instead, when the fungi are combined with the feces in the gardens, they degrade the feces into a form the termites can eat and fully digest. There are also two families of ambrosia beetle that feed their larvae on hyphae they rear in dead or dying wood, which makes them lumber pests.

18. For descriptions of large nests, see, e.g., AA Moreira, LC Forti, APP Andrade, MAC Boaretto, JFS Lopes 2004, Nest architecture of Atta laevigata, Stud. Neotrop. Fauna Environ. 39: 109–116; and JCM Jonkman 1980, The external and internal structure and growth of nests of the leafcutting ant Atta vollenweideri, Part II, Z Angew. Entomol. 89: 217–246.

19. C Kleineidam, R Ernst, F Roces 2001, Wind-induced ventilation of the giant nests of the leaf-cutting ant Atta vollenweideri, Naturwissenschaften 88: 301–305.

20. H Herz, W Beyschlag, B Hölldobler 2007, Herbivory rate of leaf-cutting ants in a tropical moist forest in Panama at the population and ecosystem scales, Biotropica 39: 482–488.

21. M Bass, JM Cherrett 1995, Fungal hyphae as a source of nutrients for the leaf-cutting ant Atta sexdens, Physiol. Entomol. 20: 1–6.

22. JC Moser 2006, Complete excavation and mapping of a Texas leafcutting ant nest, Ann. Entomol. Soc. Am. 99: 891–897.

23. Some Acromyrmex with colonies of a few thousand have minors and majors that differ little in size, but there is still a division of labor: majors cut and carry leaves and minors tend the gardens.

24. George F. Oster and Edward O. Wilson, Caste and Ecology in the Social Insects (Princeton: Princeton University Press, 1978), p. 22.

25. William H. Davidow and Michael S. Malone, The Virtual Corporation: Structuring and Revitalizing the Corporation for the 21st Century (New York: Harper Collins, 1992), p. 167.

26. There is no full-time gardener worker caste. Description based on EO Wilson 1980, Caste and division of labor in leaf-cutting ants, I: The overall pattern in A. sexdens, Behav. Ecol. Sociobiol. 7: 143–156.

27. Such microbes remain in the gardens at low levels and are so little known that some may prove to be vital to the ants; see RJ Quinlan, JM Cherrett 1978, Studies on the role of the infrabuccal pocket of the leaf-cutting ant Acromyrmex octospinosus, Insectes Soc. 25: 237–245.

28. M Bass, JM Cherrett 1996, Leaf-cutting ants prune their fungus to increase and direct its productivity, Funct. Ecol. 10: 55–61.

29. M Bass, JM Cherrett 1996, Fungus garden structure in the leaf-cutting ant Atta sexdens, Symbiosis 21: 9–24.

30. Data on the size of the trail systems and the costs of trail construction and mantenance are from JJ Howard 2001, cited in n. 9.

31. Bert Hölldobler, personal communication; and M Autori 1947, Combate a formiga saúva, Biológico 13: 196–199.

32. AG Farji-Brener, C Sierra 1998, The role of trunk trails in the scouting activity of the leaf-cutting ant Atta cephalotes, Ecoscience 5: 271–274.

33. These ideas about what has been described earlier as “recruitment overrun” are based on leaf baits left on the ground near trunk trails. See JD Sheperd 1982, Trunk trails and the searching strategy of a leaf-cutter ant, Atta colombica, Behav. Ecol. Sociobiol. 11: 77–84.

34. A Trewavas 2005, Green plants as intelligent organisms, Trends Plant Sci. 10: 413–419; and F López, JM Serrano, FJ Acosta 1994, Parallels between the foraging strategies of ants and plants, Trends Ecol. Evol. 9: 150–153.

35. See, e.g., B Hölldobler 1976, Recruitment behavior, home range orientation and territoriality in harvester ants, Pogonomyrmex, Behav. Ecol. Sociobiol. 1: 3–44. Some trails are marked with colony-specific territorial odors; see JFA Traniello, Recruitment communication, in Encyclopedia of Insects, 2nd ed., ed. Vincent H. Resh and Ring T. Cardé (New York: Academic Press, 2009), pp. 980–987.

36. JC Crick, JP Grime 1987, Morphological plasticity and mineral nutrient capture in two herbaceous species of contrasted ecology, New Phytol. 107: 403–414.

37. SEF Evison, AG Hart, DE Jackson 2008, Minor workers have a major role in the maintenance of leafcutter ant pheromone trails, Anim. Behav. 75: 963–969.

38. AG Farji-Brener, G Barrantes, O Laverde, K Fierro-Calderón, F Bascopé, A López 2007, Fallen branches as part of leaf-cutting ant trails: Their role in resource discovery and leaf transport rates in Atta cephalotes, Biotropica 39: 211–215.

39. LL Rockwood, SP Hubble 1987, Host-plant selection, diet diversity, and optimal foraging in a tropical leafcutting ant, Oecologia 74: 55–61.

40. EO Wilson 1984, Clockwork lives of the Amazonian leafcutter army, Smithsonian 15: 92–101.

41. M Burd, D Archer, N Aranwela, DJ Stradling 2002, Traffic dynamics of the leaf-cutting ant, Atta cephalotes, Am. Nat. 159: 283–293.

42. A Dussutour, S Beshers, J-L Deneubourg, V Fourcassié 2007, Crowding increases foraging efficiency in the leaf-cutting ant Atta colombica, Insectes Soc. 54: 158–165.

43. Delia Goetz and Sylvanus G. Morley, Popol Vuh: The Sacred Book of the Ancient Quiché Maya, from the Spanish translation by Adrián Recinos (Norman: University of Oklahoma Press, 1950), p. 83.

44. C Anderson, JLV Jadin 2001, The adaptive benefit of leaf transfer in Atta colombica, Insectes Soc. 48: 404–405.

45. HL Vasconcelos, JM Cherrett 1996, The effect of wilting on the selection of leaves by the leaf-cutting ant Atta laevigata, Entomol. Exp. Appl. 78: 215–220.

46. AG Hart, FLW Ratnieks 2001, Leaf caching in the leafcutting ant Atta colombica: Organizational shift, task partitioning and making the best of a bad job, Anim. Behav. 62: 227–234.

47. SP Hubbell, LK Johnson, E Stanislav, B Wilson, H Fowler 1980, Foraging by bucket-brigade in leaf-cutter ants, Biotropica 12: 210–213.

48. SG Rudolph, C Loudon 1986, Load size selection by foraging leaf-cutter ants (Atta cephalotes), Ecol. Entomol. 11: 401–410.

49. JJ Bartholdi III, LA Bunimovich, DD Eisenstein 1999, Dynamics of two- and three-worker “bucket brigade” production lines, Oper. Res. 47: 488–491.

50. AG Hart, FLW Ratnieks 2001, cited in n. 46.

51. SP Hubbell, LK Johnson, E Stanislav, B Wilson, H Fowler 1980, cited in n. 47.

52. Thomas Belt, The Naturalist in Nicaragua (London: John Murray, 1874), p. 76. The migration had been forced upon the ants by carbolic acid poured into their nest to stop them from invading a garden. What intrigues is that they managed to partition the labor of transporting their gardens in this way under such an unnatural circumstance.

53. JJ Howard, ML Henneman, G Cronin, JA Fox, G Hormiga 1996, Conditioning of scouts and recruits during foraging by a leaf-cutting ant, Atta colombica, Anim. Behav. 52: 229–306. Others have shown that unfamiliar food can be preferred; see, e.g., JM Cherrett, Chemical aspects of plant attack by leaf-cutting ants, in Phytochemical Ecology, ed. JB Harbourne (New York: Academic Press, 1972), pp. 13–24.

54. F Roces, B Hölldobler 1994, Leaf density and a trade-off between load-size selection and recruitment behavior in the ant Atta cephalotes, Oecologia 97: 1–8.

55. Bees can also minor in other flowers; see, e.g., B Heinrich 1979, “Majoring” and “minoring” by foraging bumblebees, Bombus vagans: An experimental analysis, Ecology 60: 245–55.

56. PD Coley, TM Aide 1989, Red coloration of tropical young leaves: A possible antifungal defence? J. Trop. Ecol. 5: 293–300.

57. JJ Howard, Resource quality and cost in the foraging of leaf-cutter ants, in Ant-Plant Interactions, ed. Camilla R. Huxley and David F. Cutler (New York: Scientific, 1991), pp. 42–50.

58. CM Nichols-Orians, JC Schultz 1990, Interactions among leaf toughness, chemistry, and harvesting by attine ants, Ecol. Entomol. 15: 311–320.

59. The loss of toxins during domestication is often mentioned but needs documentation for human crops (Dorian Fuller, personal communication).

60. K Jaffe, Leaf-cutting ants, in Encyclopedia of Entomology, 2nd edition, ed. John L. Capinera (New York: Springer-Verlag, 2008), pp. 2151–2160; and HL Vasconcelos 1999, Levels of leaf herbivory in Amazonian trees from different stages in forest regeneration, Acta Amazon. 29: 615–623.

61. Andreas Schaller, ed., Induced Plant Resistance to Herbivory (New York: Springer-Verlag, 2008).

62. JJ Howard 1990, Infidelity of leafcutting ants to host plants: Resource heterogeneity or defense induction? Oecologia 82: 394–401.

63. JM Cherrett, Resource conservation by the leaf-cutting ant Atta cephalotes in tropical rain forest, in Tropical Rain Forest: Ecology and Management, ed. SL Sutton, TC Whitmore (Oxford: Blackwell, 1983), pp. 253–263. In chapter 6, we saw that army ants similarly “prune” populations of their prey.

64. See Wirth, Herz, Ryel, Beyschlag, and Hölldobler, Herbivory of Leaf-Cutting Ants, cited in n. 1; and B Haines, Impact of leaf-cutting ants on vegetation development at Barro Colorado Island, in Tropical Ecological Systems, ed. FG Golley, E Medina (New York: Springer-Verlag, 1975), pp. 99–111.

65. JJ Knapp, PE Howe, A Kermarrec, Factors controlling foraging patterns in the leaf-cutting ant Acromyrmex octospinosus, in Applied Myrmecology: A World Perspective, ed. Robert K. Vander Meer, Klaus Jaffé, and Araqua Cedano (Boulder, Colo.: Westview Press, 1990), pp. 382–409.

66. RD North, CW Jackson, PE Howse 1999, Communication between the fungus garden and workers of the leaf-cutting ant, Atta sexdens rubropilosa, regarding choice of substrate for the fungus, Physiol. Entomol. 24: 127–133; and P. Ridley, PE Howse, CW Jackson 1996, Control of the behaviour of leaf-cutting ants by their “symbiotic” fungus, Experientia 52: 631–635.

67. R Wirth, W Beyschlag, RJ Ryel, B Hölldobler 1997, Annual foraging of the leaf-cutting ant Atta colombica in a semideciduous rain forest in Panama, J. Trop. Ecol. 13: 741–757.

68. Leafcutters particularly favor seeds with elaiosomes; see IR Leal, PS Oliveira 1998, Interactions between fungus-growing ants (Attini), fruits and seeds in cerrado vegetation in southeast Brazil, Biotropica 30: 170–178.

69. One desert-dwelling Acromyrmex drinks from nectaries, but this is not surprising, since it depends on dried vegetation for its gardens and therefore cannot feed on plant sap; see JK Wetterer, AG Himler, MM Yospin 2001, Foraging ecology of the desert leaf-cutting ant, Acromyrmex versicolor, in Arizona, Sociobiology 37: 633–650.

70. DH Feener, KAG Moss 1990, Defense against parasites by hitchhikers in leaf-cutting ants: A quantitative assessment, Behav. Ecol. Sociobiol. 26: 17–29.

71. DH Feener, BV Brown 1993, Oviposition behavior of an ant-parasitizing fly, Neodohrniphora curvinervis, and defense behavior by its leaf-cutting ant host Atta cephalotes, J. Insect Behav. 6: 675–688.

72. Hitchhiking continues at night; presumably nocturnal riders use the time to scrub clean the leaf booty; see MR Orr 1992, Parasitic flies influence foraging rhythms and caste division of labor in the leaf-cutter ant, Atta cephalotes, Behav. Ecol. Sociobiol. 30: 395–402.

73. Flavio Roces, personal communication; and F Roces, B Hölldobler 1996, Use of stridulation in foraging leaf-cutting ants: Mechanical support during cutting or short-range recruitment signal? Behav. Ecol. Sociobiol. 39: 293–299.

74. H Markl, Manipulation, modulation, information, cognition: Some of the riddles of communication, in Experimental Behavioral Ecology and Sociobiology, ed. B Hölldobler, M Lindauer (Sunderland, Mass.: Sinauer, 1985), pp. 163–194. For more on modulatory signals, see Bert Hölldobler and Edward O. Wilson, The Superorganism (New York: W.W. Norton, 2008), pp. 231–235.

75. F Roces, B Hölldobler 1995, Vibrational communication between hitchhikers and foragers in leaf-cutting ants (Atta cephalotes), Behav. Ecol. Sociobiol. 37: 297–302.

76. See, e.g., CB Yackulic, OT Lewis 2007, Temporal variation in foraging activity and efficiency and the role of hitchhiking behaviour in the leaf-cutting ant, Atta cephalotes, Entomol. Exp. Appl. 125: 125–134; and EHM Vieira-Neto, FM Mundim, HL Vasconcelos 2006, Hitchhiking behaviour in leaf-cutter ants: An experimental evaluation of three hypotheses, Insectes Soc. 53: 326–332.

77. WOH Hughes, D Goulson 2001, Polyethism and the importance of context in the alarm reaction of the grass-cutting ant, Atta capiguara, Behav. Ecol. Sociobiol. 49: 503–508. As with the marauder ant, the vibrations can be another kind of distress signal: when a nest chamber collapses, the calls of buried ants attract the rescue squad that digs them out.

78. Relatively little aggressive behavior has been recorded between leafcutters, though Jack Longino told me of a monthlong battle between Atta cephalotes and Atta colombica in Corcovado, Costa Rica; see also MEA Whitehouse, K Jaffe 1996, Ant wars: Combat strategies, territoriality and nest defence in the leaf-cutting ant Atta laevigata, Anim. Behav. 51: 1207–1217. Such confrontations may go largely unseen in the canopy. But leaf cutting is likely to reduce the productivity of the trees on which aggressive canopy ants of other species depend, and it is known that some of these dominant ants fight with leafcutters; see JK Wetterer 1994, Attack by Paraponera clavata prevents herbivory by the leaf-cutting ant, Atta cephalotes, Biotropica 26: 462–465; and n. 1.

79. A queen can rear workers if her garden fails, though it’s unknown whether her workers can forage for a replacement fungus; see H Fernández-Marín, WT Wcislo 2005, Production of minima workers by gynes of Atta colombica that lack a fungal pellet, J. Kansas Entomol. Soc. 78: 290–292.

80. MB Dijkstra, DR Nash, JJ Boomsma 2005, Self-restraint and sterility in workers of Acromyrmex and Atta leafcutter ants, Insectes Soc. 52: 67–76.

81. AS Yang 2007, Thinking outside the embryo: The superorganism as a model for evodevo studies, Biol. Theory 2: 398–408.

82. EO Wilson 1983, Caste and division of labor in leaf-cutter ants, IV: Colony ontogeny of A. cephalotes, Behav. Ecol. Sociobiol. 14: 55–60.

83. JK Wetterer 1994, Ontogenetic changes in forager polymorphism and foraging ecology in the leaf-cutting ant Atta cephalotes, Oecologia 98: 235–238.

84. A Powell, S Shennan, MG Thomas 2009, Late Pleistocene demography and the appearance of modern human behavior, Science 324: 1298–1301; Elman R. Service, Origins of the State and Civilization (New York: W. W. Norton, 1975).

85. Overlap in generations, the reproductive division of labor, and cooperative care of the young are considered the essential attributes of the most complex, or eusocial, insect societies, which include all ant species except possibly a few that lack distinct queens.

15. The Origins of Agriculture

1. I recommend the review by TR Schultz, UG Mueller, CR Currie, SA Rehner, Reciprocal illumination: A comparison of agriculture in humans and in fungus-growing ants, in Insect-Fungal Associations: Ecology and Evolution, ed. FE Vega, M Blackwell (Oxford: Oxford University Press), pp. 149–190. Versions of the slovenly ant hypothesis have involved fungus growth on animal matter, vegetable matter, fecal matter, or plant roots; see UG Mueller, TR Schultz, CR Currie, RMM Adams, D Malloch 2001, The origin of the attine ant-fungus mutualism, Q. Rev. Biol. 76: 169–197.

2. Stephen B. Brush and Monica L. Smith, personal communications; Stephen B. Brush, Farmers’ Bounty: Locating Crop Diversity in the Contemporary World (New Haven: Yale Univ. Press, 2004); Stephen Budiansky, The Covenant of the Wild: Why Animals Chose Domestication (New Haven: Yale University Press, 1999); and David Rindos, The Origins of Agriculture (New York: Academic Press, 1984).

3. One group of ants feeds the pellets to its larvae, such that the workers “combine the contents of the dust-bin and garbage-can and serve up the mixture as appropriate food for their young—a truly remarkable example of food-conservation”; see WM Wheeler, IW Bailey 1920, The feeding habits of pseudomyrmine and other ants, Trans Am. Philos. Soc. 22: 235–279.

4. With their lumpy bodies, Proatta also look like Atta leafcutters, which is how they got their name; see MW Moffett 1986, Behavior of Malayan group-predatory ant Proatta butteli: An Old-World relative of attine ants, Insectes Soc. 33: 444–457. The closest living relative of fungus-growing ants has untidy habits similar to Proatta; see C Rabeling, M Verhaagh, UG Mueller 2006, Behavioral ecology and natural history of Blepharidatta brasiliensis, Insectes Soc. 53: 300–306; and JLM Diniz, CRF Brandão, CI Yamamoto 1998, Biology of Blepharidatta ants, the sister group of the Attini: A possible origin of fungus-ant symbiosis, Naturwissenschaften 85: 270–274.

5. RP Coppinger, CK Smith 1983, The domestication of evolution, Environ. Conserv. 10: 283–292.

6. Feeding on fungi is not without precedent in ants: one Malayan species specializes on free-living mushrooms that it ferments in the nest before eating; see V Witte, U Maschwitz 2008, Mushroom harvesting ants in the tropical rain forest, Naturwissenschaften 95: 1049–1054.

7. CJ Krebs, R Boonstra, S Boutin, ARE Sinclair 2001, What drives the 10-year cycle of snowshoe hares? Bioscience 51: 25–35.

8. Asexual reproduction and other features of the fungus mutualism were predicted in MM Martin 1992, The evolution of insect-fungus associations: From contact to stable symbiosis, Am. Zool. 32: 593– 605. Martin based his ideas on R Law, Evolution in a mutualistic environment, in The Biology of Mutualism: Ecology and Evolution, ed. DH Boucher (New York: Oxford Univ. Press, 1985), pp. 145–170.

9. The fungus’s occasional success in sexual reproduction, presumably at these times, is shown by genetic evidence; see AS Mikheyev, UG Mueller, P Abbot 2006, Cryptic sex and many-to-one coevolution in the fungus-growing ant symbiosis, Proc. Natl. Acad. Sci. 103: 10702–10706.

10. For an exception, see, e.g., GH Perry et al. 2007, Diet and the evolution of human amylase gene copy number variation, Nat. Genet. 39: 1256–1260.

11. B Stadler, AFG Dixon 2005, Ecology and evolution of aphid-ant interactions, Annu. Rev. Ecol. Evol. Syst. 36: 345–372.

12. JS LaPolla, TR Schultz, KM Kjer, JF Bischoff 2006, Phylogenetic position of the ant genus Acropyga and the evolution of trophophoresy, Insect Syst. Evol. 37: 197–212.

13. M Dill, DJ Williams, U Maschwitz 2002, Herdsmen ants and their mealybug partners, Abh. Senckenberg. Naturforsch. Ges. 557: 1–373.

14. H Fernández-Martín, JK Zimmerman, SA Rehner, WT Wcislo 2006, Active use of the metapleural glands by ants in controlling fungal infection, Proc. R. Soc. Lond. Ser. B 273: 1689–1695. In leafcutter ants, the metapleural gland almost certainly plays a role in fungus garden health by keeping the pH low enough to selectively poison undesirable microbes; see D Ortius-Lechner, R Maile, ED Morgan, JJ Boomsma 2000, Metapleural gland secretions of the leaf-cutter ant Acromyrmex octospinosus: New compounds and their functional significance, J. Chem. Ecol. 26: 1667–1683.

15. MW Moffett 2007, Able bodies, National Geographic, 212: 140–151. A similar-seeming ant behavior occurs in a dissimilar situation: with a parasitic ant that climbs on other species to steal the nectar in their mandibles; see F-J Richard, A Dejean, J-P Lachaud 2004, Sugary food robbing in ants: A case of temporal cleptobiosis, Comptes Rendus Biol. 327: 509–517. The function of the “cleaning” behavior is unclear for ants and for most cleaning fish as well; see, e.g., R Bshary, AS Grutter 2006, Image scoring and cooperation in a cleaner fish mutualism, Nature 441: 975–978; and R Poulin, AS Grutter 1996, Cleaning symbioses: Proximate and adaptive explanations, Bioscience 46: 512–517. The Dorymyrmex species is probably smithi (Stefan Cover, personal communication).

16. F Amante 1967, Prejuízos causados pela formiga saúva em plantações de Eucalyptus e Pinus no Estado de São Paulo, Silvicul. São Paulo 6: 355–363; and M Autuori 1947, Contribuição para o conhecimento de saúva (Atta spp IV): Osauveiro depois da primeira revoada (Atta sexdens rubripilosa), Arq. Inst. Biol. 18: 39–70.

17. It’s called the infrabuccal pocket; see CR Currie, AE Stuart 2001, Weeding and grooming of pathogens in agriculture by ants, Proc. R. Soc. Lond. Ser. B 268: 1033–1039.

18. AEF Little, T Murakami, UG Mueller, CR Currie 2006, Defending against parasites: Fungus-growing ants combine specialized behaviours and microbial symbionts to protect their fungus gardens, Biol. Lett. 2: 12–16.

19. The linkage between the species may be tighter for some of Atta’s fungus-growing relatives (which culture the bacteria on special “crypts” on their bodies) than Atta itself; see UG Mueller, D Dash, C Rabeling, A Rodrigues 2008, Coevolution between attine ants and actinomycete bacteria: A reevaluation, Evolution 62: 2894–2912; and CR Currie, M Poulsen, J Mendenhall, JJ Boomsma, J Billen 2006, Coevolved crypts and exocrine glands support mutualistic bacteria in fungus-growing ants, Science 311: 81–83.

20. MJF Brown, ANM Bot, AG Hart 2006, Mortality rates and division of labor in the leaf-cutting ant, Atta colombica, J. Insect Sci. 6: 1–8.

21. Among people, sanitation positions are made more desirable by relatively high pay and good job benefits; see Elizabeth Royte, Garbage Land: On the Secret Trail of Trash (London: Little, Brown, 2005).

22. ANM Bot, CR Currie, AG Hart, JJ Boomsma 2001, Waste management in leaf-cutting ants, Ethol. Ecol. Evol. 13: 225–237.

23. AG Hart, ANM Bot, MJF Brown 2002, A colony-level response to disease control in a leaf-cutting ant, Naturwissenschaften 89: 275–277.

24. HM Hull-Sanders, JJ Howard 2003, Impact of Atta colombica colonies on understory vegetation and light availability in a neotropical forest, Biotropica 35: 441–445; and AG Farji-Brener, AE Illes 2000, Do leaf-cutting ant nests make “bottom-up” gaps in neotropical rain forests? A critical review of the evidence, Ecol. Lett. 3: 219–227.

25. In one forest in Costa Rica all the soil is turned over by leafcutters every two or three centuries—fast work from the standpoint of a tree; see I Perfecto, J Vandermeer 1993, Distribution and turnover rate of a population of Atta cephalotes in a tropical rain forest in Costa Rica, Biotropica 25: 316–321.

26. LSL Sternberg, MC Pinzon, MZ Moreira, P Moutinho, EI Rojas, EA Herre 2007, Plants use macronutrients accumulated in leaf-cutting ant nests, Proc. R. Soc. Lond. Ser. B 274: 315–321; and BL Haines 1978, Element and energy flows through colonies of the leaf-cutting ant, Atta colombica, in Panama, Biotropica 10: 270–277.

27. AG Farji-Brener 2005, The effect of abandoned leaf-cutting ant nests on plant assemblage composition in a tropical rainforest of Costa Rica, Ecoscience 12: 554–560; and AG Farji-Brener, CA Medina 2000, The importance of where to dump the refuse: Seed banks and fine roots in nests of the leaf-cutting ants Atta cephalotes and Atta colombica, Biotropica 32: 120–126.

28. Young plants may survive for a time in the surface refuse of Atta colombica, where sanitation ants troll for waste but their plant-snipping sisters fear to tread; see Alejandro Farji-Brener (personal communication) and M Garrettson, JF Stetzel, BS Halpern, DJ Hearn, BT Lucey, MJ McKone 1998, Diversity and abundance of understorey plants on active and abandoned nests of leaf-cutting ants (Atta cephalotes) in a Costa Rican rain forest, J. Trop. Ecol. 14: 17–26.

29. JW Dalling, R Wirth 1998, Dispersal of Miconia argentea seeds by the leaf-cutting ant Atta colombica, J. Trop. Ecol. 14: 705–710.

30. I wouldn’t be surprised if the costs to an ant plant of maintaining a symbiosis with ants can at times approach the costs in lost foliage from leafcutters and herbivores for many plants; see, e.g., M Heil, B Fiala, KE Linsenmair, G Zotz, P Menke, U Maschwitz 1997, Food body production in Macaranga triloba: A plant investment in anti-herbivore defense via symbiotic ant partners, J. Ecol. 85: 847–861.

31. The “higher attines” include the leafcutters (Acromyrmex and Atta) and at least two other genera that use dried leaves for their gardens.

32. Even leafcutters excrete on their mulch to get the garden started, much as human farmers use compost and manure.

33. For this timeline and details, see TR Schultz, SG Brady 2008, Major evolutionary transitions in ant agriculture, Proc. Natl. Acad. Sci. 105: 5435–5440; UG Mueller, C Rabeling 2008, A breakthrough innovation in animal evolution, Proc. Natl. Acad. Sci. 105: 5287– 5288.

34. The “ecological release” that results from moving of a species away from its parasites and competitors can lead to expanded resource use in what can be thought of as a “transplanted landscape”; see Edgar Anderson, Plants, Man, and Life (Boston: Little, Brown, 1952); and chapter 16.

35. As the earliest farming communities grew, people became smaller, weaker, and more disease ridden than their hunter-gatherer ancestors; see T. Douglas Price and Anne Birgitte Gebauer, eds., Last Hunters, First Farmers: New Perspectives on the Prehistoric Transition to Agriculture (Santa Fe: School of American Research, 1995). The idea of a “plant trap” is described in Robert L. O’Connell, Ride of the Second Horseman: The Birth and Death of War (New York: Oxford University Press, 1995).

36. ANM Bot, SA Rehner, JJ Boomsma 2001, Partial incompatibility between ants and symbiotic fungi in two sympatric species of Acromyrmex leaf-cutting ants, Evolution 55: 1980–1991.

37. These incompatibility reactions are known for the genus Acromyrmex; see M Poulsen, JJ Boomsma 2005, Mutualistic fungi control crop diversity in fungus-growing ants, Science 307: 741–744.

38. See n. 36; AS Mikheyev, UG Mueller, JJ Boomsma 2007, Population genetic signatures of diffuse co-evolution between leaf-cutting ants and their cultivar fungi, Mol. Ecol. 16: 209–216; and RMM Adams, UG Mueller, AK Holloway, AM Green, J Narozniak 2000, Garden sharing and garden stealing in fungus-growing ants, Naturwissenschaften 87: 491–493.

39. MB Dijkstra, JJ Boomsma 2003, Gnamptogenys hartmani: An agro-predator of Trachymyrmex and Sericomyrmex fungus-growing ants, Naturwissenschaften 90: 568–571; and RMM Adams, UG Mueller, TR Schultz, B Norden 2000, Agropredation: Usurpation of attine fungus gardens by Megalomyrmex ants, Naturwissenschaften 87: 549–554.

40. T Yamaguchi 1995, Intraspecific competition through food robbing in the harvester ant, Messor aciculatus, and its consequences on colony survival, Insectes Soc. 42: 89–101; and B Hölldobler 1986, Food robbing in ants, a form of interference competition, Oecologia 69: 12–15.

41. J Diamond 1998, Ants, crops, and history, Science 281: 1974–1975. For human examples, see Jared Diamond, Guns, Germs, and Steel: The Fates of Human Societies (New York: Norton, 1997).

42. Among other things, the ants provide the fungus with ideal temperature, humidity, and oxygen levels. One article examines the relationship from the fungus’s point of view; see UG Mueller 2002, Ant versus fungus versus mutualism: Ant cultivar conflict and the deconstruction of the attine ant-fungus symbiosis, Am. Nat. 160: S67–S98.

16. Armies of the Earth

1. Battle mortalities and border changes are described in ML Thomas, CM Payne-Makrisâ, AV Suarez, ND Tsutsui, DA Holway 2006, When supercolonies collide: Territorial aggression in an invasive and unicolonial social insect, Mol. Ecol. 15: 4303–4315.

2. Until recently the Argentine ant was known as Iridomyrmex humilis. In its native range, it also crosses the Argentina border into adjacent parts of Uruguay, Paraguay, and Brazil.

3. J Zee, DA Holway 2006, Nest raiding by the invasive Argentine ant on colonies of the harvester ant, Pogonomyrmex subnitidus, Insectes Soc. 53: 161– 167. A more general look at competitive displacement can be found in DA Holway 1999, Competitive mechanisms underlying the displacement of native ants by the invasive Argentine ant, Ecology 80: 238– 251; and KG Human, DM Gordon 1999, Behavioral interactions of the invasive Argentine ant with native ant species, Insectes Soc. 46: 159–163.

4. AV Suarez, DA Holway, TJ Case 2001, Patterns of spread in biological invasions dominated by long-distance jump dispersal: Insights from Argentine ants, Proc. Natl. Acad. Sci. 98: 1095–1100.

5. FR Cole, AC Medeiros, LL Loope, WW Zuehlke 1992, Effects of the Argentine ant on arthropod fauna of Hawaiian high-elevation shrubland, Ecology 73: 1313–1322.

6. DA Holway, E LeBrun, C Tillberg, AV Suarez 2007, Trophic ecology of invasive Argentine ants in their native and introduced ranges, Proc. Natl. Acad. Sci. 104: 20856–20861.

7. AV Suarez, JQ Richmond, TJ Case 2000, Prey selection in horned lizards following the invasion of Argentine ants in southern California, Ecol. Appl. 10: 711–725.

8. CE Christian 2001, Consequences of a biological invasion reveal the importance of mutualism for plant communities, Nature 413: 635–639.

9. SE Carney, MB Byerley, DA Holway 2003, Invasive ants (Linepithema humile) do not replace native ants as seed dispersers of Dendromecon rigida, Oecologia 135: 576–582.

10. It’s not known whether any stolen pupae are ever reared as slaves, either deliberately or by accident. Both seem unlikely, given how strongly the ants abhor the scent of workers from neighboring colonies.

11. The last two rank with the Argentine ant among the hundred worst invasive species; see S Lowe, M Browne, S Boudjelas, M De Poorter 2004, 100 of the world’s worst invasive alien species: A selection from the Global Invasive Species Database, Invasive Species Specialist Group, Gland, Switzerland; available as a PDF booklet at www.issg.org. Two other ants make the list: Anoplolepis gracilipes (originally African or Asian) and Pheidole megacephala (probably originally African).

12. My thanks to Alex Wild for the sports analogy. The only ants outside Argentina that have had any luck fighting the sugar ant are in Australia, aided perhaps by the severity of the climate; see ML Thomas, DA Holway 2005, Condition-specific competition between invasive Argentine ants and Australian Iridomyrmex, J. Anim. Ecol. 74: 532–542.

13. This behavior can also occur between competing species; see, e.g., TA Langen, F Tripet, P Nonacs 2000, The red and the black: Habituation and the dear-enemy phenomenon in two desert Pheidole ants, Behav. Ecol. Sociobiol. 48: 285–292.

14. David Holway, personal communication; see also n. 4.

15. The genetic diversity of Argentine ants in the southern United States suggests that their rapid expansion was effected in part through multiple invasions of different source colonies by way of several southern port cities soon after their arrival in New Orleans.

16. DA Holway, AV Suarez, TJ Case 1998, Loss of intraspecific aggression in the success of a widespread invasive social insect, Science 282: 949–952. This paper was written prior to Melissa Thomas’s discovery of supercolonies.

17. These native habitats at best sustain patchy populations of Argentine ants; see NE Heller, KK Ingram, DM Gordon 2008, Nest connectivity and colony structure in unicolonial Argentine ants, Insectes Soc. 55: 397–403; and DA Holway, AV Suarez 2006, Homogenization of ant communities in Mediterranean California: The effects of urbanization and invasion, Biol. Conserv. 127: 319–326.

18. The relocation of nests relative to foodstuffs has been documented for another species with decentralized colonies; see chapter 9 and E van Wilgenburg, MA Elgar 2007, Colony structure and spatial distribution of food resources in the polydomous meat ant Iridomyrmex purpureus, Insectes Soc. 54: 5–10.

19. D Helbing, J Keltsch, P Molnár 1997, Modelling the evolution of human trail systems, Nature 388: 57–50.

20. The use of exploratory trails to integrate untouched terrain into a territory was first shown in EO Wilson 1962, Chemical communication among workers of the fire ant Solenopsis saevissima, 1: The organization of mass foraging, Anim. Behav. 10: 134– 147. It’s unknown if such trail cues disappear after an area has been incorporated into a territory, or whether they continue to be laid at some level, e.g., at the start of daily bouts of foraging.

21. J-L Deneubourg, S Aron, S Goss, JM Pasteels 1990, The self-organizing exploratory pattern of the Argentine ant, J. Insect Behav. 3: 159–168. This research was done on colony fragments of 150 to 1,200 workers and a foraging arena less than a meter square.

22. This pattern may arise if foragers travel independently but shift course each time two come into contact; see DM Gordon 1995, The expandable network of ant exploration, Anim. Behav. 50: 995– 1007. Curiously, this study found no evidence of exploratory trails.

23. My own observations and those of George Markin suggest it might take the ants many attempts to catch large prey; see GP Markin 1970, Foraging behavior of the Argentine ant in a California citrus grove, J. Econ. Entomol. 63: 740–744.

17. The Immortal Society

1. Dangsheng Liang, personal communication.

2. Edward O. Wilson, Sociobiology: The New Synthesis (Cambridge: Harvard University Press, 1975), 7. A society can also be an amalgamation of more than one species, as discussed later in this chapter.

3. Through powerful identity labels, nationalism among people today provides for bonds and a sense of kinship even among strangers; see Karl W. Deutsch, Nationalism and Social Communication (Cambridge, MA: MIT Press, 1996).

4. D Liang, J Silverman 2000, “You are what you eat”: Diet modifies cuticular hydrocarbons and nestmate recognition in the Argentine ant, Linepithema humile, Naturwissenschaften 87: 412–416. As this book goes to press, the identity of the compounds used by Argentine ants to identify enemies are being determined; M Brandt, E van Wilgenburg, R Sulc, KJ Shea, ND Tsutsui 2009, The scent of supercolonies: the discovery, synthesis and behavioral verification of ant colony recognition cues, BMC Biol. in press.

5. MA Elgar, RA Allan 2006, Chemical mimicry of the ant Oecophylla smaragdina by the myrmecophilous spider Cosmophasis bitaeniata: Is it colony-specific? J. Ethol. 24: 239–246. Other “guests,” from silverfish to beetles, survive in ant nests by cunning use of pilfered identity signals—it’s a source of amazement to me that almost none infiltrate Argentine ant colonies, suggesting their colony identity is a tough nut to crack.

6. Because of the universality of social bonding in nature, an alien coming to Earth before the evolution of man would not have picked ants as the dominant social force, as claimed by Bert Hölldobler and Edward O. Wilson in The Superorganism (New York: W.W. Norton, 2008), though I like to think aliens would be as fascinated with ants as I am. Even microbes arose through the social union of smaller microbes, and those in turn through a union of complex molecules; see Lynn Margulis, Symbiotic Planet: A New Look at Evolution (New York: Basic Books, 1999).

7. One review suggests that treating a colony as an individual is more enlightening than treating it more narrowly as a superorganism; see A Hamilton, NR Smith, MH Haber, Social insects and the individuality thesis: Cohesion and the colony as a selectable individual, in Organization of Insect Societies: From Genome to Sociocomplexity, ed. Jürgen Gadau and Jennifer Fewell (Cambridge, MA: Harvard University Press, 2009), pp. 572–589. While this view has merit in some of the situations these authors discuss, parallels to organisms can both be compelling and lead to useful models (see Conclusion). For reviews of the evolution of identity, see ND Tsutsui 2004, Scents of self: The expression component of self/non-self recognition systems, Ann. Zool. Fenn. 41: 713–727; CM Payne, CV Tillberg, AV Suarez 2004, Recognition systems and biological invasions, Ann. Zool. Fenn. 41: 843–858; and John Maynard Smith and Eörs Szathmáry, The Major Transitions in Evolution (San Francisco: W.H. Freeman, 1995).

8. Crematogaster levior ants can share a garden with any of several alternative ant species. Nevertheless, they manage to recognize workers of the resident colony, distinguishing them from all other alien colonies; see J Orviel, C Errard, A Dejean 1997, Ant gardens: Interspecific recognition in parabiotic ant species, Behav. Ecol. Sociobiol. 40: 87–93.

9. Actually, there is no evidence for any ant species that workers distinguish between individuals in their nest by kinship or by genetic differences, and therefore no reason to expect aggression within a colony on this basis, no matter how many queens there are and how genetically diverse the nestmates might be; see DC Queller, JE Strassmann 2002, The many selves of social insects, Science 296: 311–313. In fact, supercolonies vary in genetic diversity, and even the more diverse of them show no sign of internal squabbling; see ND Tsutsui, AV Suarez, RK Grosberg 2003, Genetic diversity, asymmetrical aggression, and recognition in a widespread invasive species, Proc. Natl. Acad. Sci. 100: 1078–1083.

10. In some cases, colony odors arise primarily in queens; see A Hefetz 2007, The evolution of hydrocarbon pheromone parsimony in ants—Interplay of colony odor uniformity and odor idiosyncrasy, Myrmecol. News 10: 59–68.

11. ML Thomas, CM Payne-Makrisâ, AV Suarez, ND Tsutsui, DA Holway 2007, Contact between supercolonies elevates aggression in Argentine ants, Insectes Soc. 54: 225–233. I am reminded of human nationalism and the tendency for experienced border folk to be more outspoken and expectant of trouble than their fellow citizens. No surprise that the greatest human empires have arisen where different ethnic populations abut each other’s territories, strengthening identity and solidarity—and often the hunger for conquest; see Peter Turchin, War and Peace and War: The Rise and Fall of Empires (New York: Plume, 2007).

12. GP Markin 1968, Nest relationships of the Argentine ant, Iridomyrmex humilis, J. Kans. Entomol. Soc. 41: 511–516.

13. Jump dispersal within a supercolony could increase genetic homogenization, however.

14. KK Ingram, DM Gordon 2003, Genetic analysis of dispersal dynamics in an invading population of Argentine ants, Ecology 84: 2832–2842.

15. This mental experiment is the colony equivalent of a “ring species,” in which individuals of a geographically variable species breed freely everywhere, but individuals at the extremes of the range are so different that they can’t interbreed.

16. It is still possible that ants might show more subtle animosity or favoritism within a colony, for example, by preferring to exchange food with genetically closer individuals (perhaps kin, but see n. 9).

17. Violence within otherwise affable supercolonies occurs in only one situation. Each spring, for reasons unclear, the workers mass-execute the queens, sparing only enough of them to maintain the high rate of colony growth. It’s an exception that proves the rule: social integrity is reflected in how well the ants manage conflict when it arises. There seems to be no resistance, and the colony operates smoothly as its queens are butchered—even the queens don’t protest. These mass executions were first described in GP Markin 1970, The seasonal life cycle of the Argentine ant, Iridomyrmex humilis, in southern California, Ann. Entomol. Soc. Am. 63: 1238–1242.

18. Clarence Day, This Simian World (New York: Alfred A. Knopf, 1920), p. 10.

19. Neil Tsutsui, quoted in M Shwartz 2004, Scientists challenge report of one Argentine ant supercolony flooding California, Stanford Report, 7 April.

20. ND Tsutsui, AV Suarez, DA Holway, TJ Case 2000, Reduced genetic variation and the success of an invasive species, Proc. Natl. Acad. Sci. 97: 5948–5953. A slightly different “genetic cleansing” hypothesis claims that, with the nests of colonists reaching extraordinary densities, any hostilities are inordinately costly, making it advantageous for the ants to evolve to lose the capacity to identify and discriminate against non-kin; see T Giraud, JS Pedersen, L Keller 2002, Evolution of supercolonies: The Argentine ants of southern Europe, Proc. Natl. Acad. Sci. 99: 6075–6079. While much has been made in published reports of the high genetic diversity in Argentina compared to that in invasive populations, almost certainly this is an artifact of genes being sampled largely between colonies in Argentina versus within single colonies in California. I think it’s likely that colonies of Argentine ants have the capacity to expand indefinitely, regardless of their genetic diversity.

Genetic losses could give a colony another kind of edge: workers from supercolonies with a lower genetic diversity, especially the Very Large Colony, exhibit quick attacks in combat with other supercolonies, using the “shock and awe” offensive approach we saw in the marauder ant. Perhaps their stripped-down recognition signals make the workers faster at distinguishing friend from foe; see ND Tsutsui, AV Suarez, RK Grosberg 2003, cited in n. 9.

21. The exception would be the colonies from one site in Argentina that each have a single, local nest; see NE Heller 2004, Colony structure in introduced and native populations of the invasive Argentine ant, Linepithema humile, Insectes Soc. 51: 378–386.

22. Argentine ants may be less inbred in Argentina, where the smaller territories mean the weak-flying males are more likely to reach neighboring colonies, potentially allowing more gene flow than we find overseas, even if most of the males are killed by workers.

23. This overlap in generations is shared by ant colonies and the cells of most organisms (see Conclusion). No wonder some scholars think our idea of an integrated, coherent self is something of an illusion. See, e.g., Daniel M. Wegner, The Illusion of Conscious Will (Cambridge, MA: MIT Press, 2003).

24. In most other ants that reproduce by fission or budding, a new nest develops a separate identity from its parent (see chapter 4, n. 18). The supercolonies of the Argentine ant (and likely some other invasive ant species) more closely resemble the individuals of some fungi that spread through soil for centuries, with one Oregon mat covering 10 square kilometers; see ML Smith, JN Bruhn, JB Anderson 1992, The fungus Armillaria bulbosa is among the largest and oldest living organisms, Nature 356: 428–431.

25. Linda Stone, Paul F. Lurquin, and Luigi Luca Cavalli-Sforza, Genes, Culture, and Human Evolution (New York: Wiley-Blackwell, 2007).

26. Species are expected to be genetically distinct, and in fact each Argentine ant supercolony has been found to have a different hydrocarbon “fingerprint”—a combination of the surface chemicals likely to be genetically determined and essential to colony (and in this case species) identity; see CW Torres, M Brandt, ND Tsutsui 2007, The role of cuticular hydrocarbons as chemical cues for nestmate recognition in the invasive Argentine ant (Linepithema humile), Insectes Soc. 54: 363–373.

27. I cite the biological species concept as defined in Ernst Mayr, Principles of Systematic Zoology (New York: McGraw Hill, 1969), p. 26. As discussed on p. 133, isolation doesn’t require a mountain range: insect populations can become isolated even within a single crown of widely separated tropical trees—the space between crowns being in effect mountain ranges in miniature. Other modes of speciation can be important as well; see, e.g., Douglas J. Futuyma, Evolution (New York: Sinauer, 2005), pp. 353–404. In practice, admittedly, Mayr himself had a double standard in distinguishing species; see M Schilthuizen 2000, Dualism and conflicts in understanding speciation, Bioessays 22: 1134–1141.

28. This may generally be how distinct colonies originate in the Argentine ant, though it’s possible that mating flights, thus far undetected in Argentina and abroad, occur on rare occasions. My hypothesis does not require any changes (in particular, convergent changes) in Argentine ants each time they are introduced abroad. Discussions of this ant have been muddied by confusion about what a colony is in this species; it is definitely not a single nest, as is often implied (see, e.g., PT Starks 2003, Selection for uniformity: Xenophobia and invasion success, Trends Ecol. Evol. 18: 159–162). Contrary to what Starks writes, Argentine ants never exhibit “indiscriminate altruism” or a “breakdown in normal nestmate discrimination behavior.”

29. Early human hunter-gatherer bands were small but relatively open and fluid because of the need for exchanging mates between groups, which meant many groups shared family ties. Our identification with fixed groups developed later, after agriculture gave rise to larger, sedentary communities that were kept together by leaders demanding tributes and allegiance. Among other mammals, herds are the largest groups, but these do not have delimited memberships and are not considered societies. Their members not only do not cooperate, e.g., in rearing young, but also exercise strong self-interest, e.g., in avoiding predators.

30. The range expansion of the Argentine ant supercolonies is likely to continue: see N Roura-Pascual, AV Suarez, C Gómez, P Pons, Y Touyama, AL Wild, AT Peterson 2004, Geographical potential of Argentine ants (Linepithema humile) in the face of global climate change, Proc. R. Soc. Lond. Ser. B 271: 2527–2534.

31. In addition to the red imported fire ant, Solenopsis invicta, discussed here, the southern United States has another destructive but less widespread invasive fire ant from Argentina, Solenopsis richteri, and several native fire ant species, none of which are harmful. See Walter R. Tschinkel, The Fire Ants (Cambridge, MA: Harvard University Press, 2006); colonies with multiple queens described on pp. 405–411.

32. EG LeBrun, CV Tillberg, AV Suarez, PJ Folgarait, CR Smith, DA Holway 2007, An experimental study of competition between fire ants and Argentine ants in their native range, Ecology 88: 63–75. Fire ants and Argentine ants appear to have shifting, broadly overlapping territories in Argentina, a pattern likely made possible by their low worker densities.

33. G Buczkowski, EL Vargo, J. Silverman 2004, The diminutive supercolony: The Argentine ants of the southeastern United States, Mol. Ecol. 13: 2235–2242.

34. Don Mabry and Pedro Jover, personal communications.

35. D Pimentel, R Zuniga, D Morrison 2005, Update on the environmental and economic costs associated with alien-invasive species in the United States, Ecol. Econ. 52: 273–288.

Conclusion

1. On the other hand, carefully framed anthropomorphisms are useful in hypotheses: R Lockwood, Anthropomorphism is not a four-letter word, in Perceptions of Animals in American Culture, ed. RJ Hoage (Washington, DC: Smithsonian Press, 1989), pp. 41–56; GM Burghardt 1985, Animal awareness: Current perceptions and historical perspective, Am. Psychol. 40: 905–919; L Daston, G Mitman, Thinking with Animals: New Perspectives on Anthropomorphism (New York: Columbia University Press, 2005); RW Mitchell, NS Thompson, HL Miles, Anthropomorphism, Anecdotes, and Animals (New York: SUNY Press, 1996).

2. Ludwig Wittgenstein, Philosophical Investigations (Oxford: Blackwell Basil, 1958), p. 178. See also J Cole, About Face (Cambridge, MA: MIT Press, 1999); C Darwin, Expression of Emotions in Man and Animals (London: John Murray, 1872).

3. D Arendt, K Nübler-Jung 1999, Comparison of early nerve cord development in insects and vertebrates, Development 126: 2309–2325; R Lichtneckert, H Reichert 2005, Insights into the urbilaterian brain: Conserved genetic patterning mechanisms in insect and vertebrate brain development, Heredity 94: 465–477.

4. Lewis Thomas, Lives of the Cell (New York: Viking Press, 1974), p. 12. Douglas R. Hofstadter subsequently made the superorganism idea come alive in his Gödel, Escher, Bach (New York: Basic Books, 1979).

5. Compounding the problem is a lack of agreement on what a “behavior” is; see DA Levitis, WZ Lidicker, G Freund 2009, Behavioural biologists do not agree on what constitutes behaviour, Anim. Behav. 78: 103–110.

6. J Gautrais, G Theraulaz, J-L Deneubourg, C Anderson 2002, Emergent polyethism as a consequence of increased colony size in insect societies, J. Theor. Biol. 215: 363–373; R Jeanson, JH Fewell, R Gorelick, SM Bertram 2007, Emergence of increased division of labor as a function of group size, Behav. Ecol. Sociobiol. 62: 289–298.

7. SK Robson, JFA Traniello, Key individuals and the organization of labor in ants, in Information Processing in Social Insects, ed. C Detrain, J-L Deneubourg, JM Pasteels (Basel: Birkhäuser Verlag, 1999), pp. 239–259; GF Oster, EO Wilson, Caste and Ecology in the Social Insects (Princeton, NJ: Princeton Univ. Press, 1978). For the dishwashing example, thanks to JH Fewell 2003, Social insect networks, Science 301: 1867–1870.

8. JT Costa 2002, Scale models? What insect societies teach us about ourselves, Proc. Am. Phil. Soc. 146: 170–180.

9. Ovid, Metamorphoses, translated by Rolfe Humphries (Bloomington: Indiana Univ. Press, 1964), p. 173.

10. Not that one form of society is more “primitive” than another, in either ants or people; nor is change necessarily equally easy in either direction (see n. 35, chapter 15).

11. This brings to mind responses to the Hurricane Katrina disaster in New Orleans, in which decentralized local groups succeeded in providing relief where the government failed: V Bier, Hurricane Katrina as a bureaucratic nightmare, in Risk and Disaster, ed. RJ Daniels, DF Kettl, H Kunreuther (Philadelphia: University of Pennsylvania Press, 2006), pp. 243–254.

12. This situation of power of the majority over their leaders, referred to as a “reverse dominance hierarchy,” is a modification of the typical linear hierarchy found in most apes: C Boehm, Hierarchy in the Forest: The Evolution of Egalitarian Behavior (Cambridge, MA: Harvard Univ. Press, 1999).

13. One World Bank official has proposed that in addressing global problems hierarchical governments be replaced by networked governance: J-F Rischard 2002, Global issues networks: Desperate times deserve innovative measures, Wash. Q. 26: 17–33.

14. H Reingold, Mobile media and political collective action, in Handbook of Mobile Communication Studies, ed. JE Katz (Cambridge, MA: MIT Press, 2008), pp. 225–239.

15. M Granovetter 1983, The strength of weak ties: A network theory revisited, Social Theory 1: 201–233.

16. James Carey, personal communication, and JR Carey 2001, Insect biodemography, Annu. Rev. Entomol. 46: 79–110.

17. PJ Wilson, The Domestication of the Human Species (New Haven: Yale University Press, 1988).

18. EA Langridge, NR Franks, AB Sendova-Franks 2004, Improvement in collective performance with experience in ants, Behav. Ecol. Sociobiol. 56: 523–529.

19. As we’ll see shortly, certain ants called ponerines have workers that can serve as queens and so do not fit this pattern, but neither do most organisms; see Leo W. Buss, The Evolution of Individuality (Princeton, NJ: Princeton University Press, 1987).

20. JW Pepper, MD Herron 2008, Does biology need an organism concept? Biol. Rev. 83: 621–627.

21. MD Herron, RE Michod 2008, Evolution of complexity in the volvocine algae: Transitions in individuality through Darwin’s eye, Evolution 62: 436–451; K Drescher, KC Leptos, I Tuval, T Ishikawa, TJ Pedley, RE Goldstein 2009, Dancing Volvox: Hydrodynamic bound states of swimming algae, Phys. Rev. Lett. 102: 168101–168105.

22. MC McCarthy, BJ Enquist 2005, Organismal size, metabolism and the evolution of complexity in metazoans, Evol. Ecol. Res. 7: 681–696.

23. L Lefebvre, D Sol 2008, Brains, lifestyles and cognition: Are there general trends? Brain Behav. Evol. 72: 135–144.

24. M Minsky, The Society of Mind (New York: Simon & Schuster, 1985).

25. M Dorigo, V Trianni, E Sahin, R Gross, TH Labella, G Baldassarre, S Nolfi, J-L Deneubourg, F Mondada, D Floreano, LC Gambardella 2004, Evolving self-organizing behaviors for a swarm-bot, Auton. Robots 17: 223–245; MJB Krieger, J-B Billeter, L Keller 2000, Ant-like task allocation and recruitment in cooperative robots, Nature 406: 992–995.

26. R Wehner, T Fukushi, K Isler 2007, On being small: Brain allometry in ants, Brain Behav. Evol. 69: 220–228; W Gronenberg 2008, Structure and function of ant brains: Strength in numbers, Myrmecol. News 11: 25–36.

27. NR Franks 1989, Army ants: A collective intelligence, Am. Sci. 77: 138–145.

28. DS Wilson, JJ Timmel, RR Miller 2004, Cognitive cooperation: When the going gets tough, think as a group, Human Nature 15: 225–250.

29. See, e.g., T Monnin, C Peeters 1999, Dominance hierarchy and reproductive conflicts among subordinates in a monogynous queenless ant, Behav. Ecol. 10: 323–332; J Heinze 2004, Reproductive conflict in insect societies, Adv. Study Behav. 34: 1–58; H Helanterä, L Sundström 2007, Worker reproduction in Formica ants, Am. Nat. 170: E14–E25; HK Reeve, B Hölldobler 2007, The emergence of a superorganism through intergroup competition, Proc. Natl. Acad. Sci. 104: 9736–9740.

30. The reproductive strategies of ponerine colonies are detailed by B Hölldobler, EO Wilson, The Superorganism (New York: W.W. Norton, 2008).

31. S Baratte, M Cobb, C Peeters 2006, Reproductive conflicts and mutilation in queenless Diacamma ants, Anim. Behav. 72: 305–311.

32. In ant societies, as in human societies, policing can serve the self-interest of individuals, the common good, or both: Peter Nonacs, personal communication, and FLW Ratnieks, T Wenseleers 2005, Policing insect societies, Science 307: 54–56.

33. A Burt, R Trivers, Genes in Conflict (Cambridge, MA: Harvard Univ. Press, 2008).

34. A Livnat, N Pippenger 2006, An optimal brain can be composed of conflicting agents, Proc. Natl. Acad. Sci. 103: 3198–3202.

35. AFG Bourke 1999, Colony size, social complexity and reproductive conflict in social insects, J. Evol. Biol. 12: 245–257.

36. In most social species other than ants and the majority of other eusocial insects, individuals can leave a group to join another group, start a group of their own, or live alone (as do human immigrants, pilgrims, and hermits). The ants’ faithfulness to their societies may serve as a measure of the strength of group selection as described in DS Wilson, EO Wilson 2007, Rethinking the theoretical foundation of sociobiology, Quart. Rev. Biol. 82: 327–348. Bonding is equally strong even among simple organisms such as sponges; see X Fernández-Busquets, The sponge as a model of cellular recognition, in Sourcebook of Models for Biomedical Research, ed. P. Michael Conn (New York: Springer, 2008), pp. 75–83.

37. NR Franks 1989, Thermoregulation in army ant bivouacs, Physiol. Entomol. 14: 397–404.

38. Because army ant colonies split (chapter 4), their reproduction is as if a human mother were to give birth to a child her own weight. Honeybees show a similar investment: J Tautz, The Buzz about Bees: Biology of a Superorganism (Heidelberg: Springer-Verlag, 2008).

39. M Maeterlinck, The Swarm from the Life of the Bee, trans. A Euwer (New York: Dodd, Mead, 1901), pp. 39, 45–46.

40. M Batty 2008, The size, scale, and shape of cities, Science 319: 769–771; LMA Bettencourt, J Lobo, D Helbing, C Kühnert, GB West 2007, Growth, innovation, scaling, and the pace of life in cities, Proc. Natl. Acad. Sci. 104: 7301–7306; JT Bonner, The Evolution of Complexity by Means of Natural Selection (Princeton, NJ: Princeton Univ. Press, 1988).

41. EO Wilson 1973, Ants of Easter Island and Juan Fernández, Pac. Insects 15: 285–287.

42. WJ Broad 1996, Paradise lost: Biosphere retooled as atmospheric nightmare, New York Times, 19 November, C1.