—John Donne
Devotions upon Emergent Occasions, Meditation XVII, 1624
Humans are social animals—at least most of us are—and it is only natural that we should have a particular affinity for those other species that exhibit similar societal instincts. We see in such animals ourselves and parallels of our own evolution. Social interactions come in a wide gradation of forms, from degrees of parental investment to large communities teeming with thousands, if not millions, of individuals. Outside of humans, almost all instances of truly complex animal societies are found among arthropods, and the majority of these are spread across the insects.
A society, of course, consists of individuals working together. The simplest social expression may be that of extended care on the part of a mother tending her brood. The insect world teems with protective mothers, ranging from earwigs to leaf beetles, and many of their behaviors are not all that different from those of birds tending their eggs or feeding their chicks. Gregarious associations, such as large aggregations of springtails or even the coordinated swarms of locusts, also represent a simple form of social behavior. In some species, insects of the same generation will come together within a common structure, such as a branching burrow underground or a thicket of spun silk in trees. Within these collective nests, the community garners the advantages of group protection, but otherwise each mother raises her own offspring independently of the others. These types of communal societies are found among tent caterpillars, some bees and wasps, and beetles.
The ultimate expression of sociality is one in which overlapping generations of females come together within a shared nest and collaborate in the care of a brood, even though the offspring come from only one or a few of the total females involved. This form of social behavior is called eusocial, a term coined in 1966 by American bee biologist Suzanne Batra (b. 1937) that literally means “truly social” (the prefix eu means “true” and is derived from the ancient Greek for “well” or “good”). Within a eusocial society some females forego their own reproduction in order to help rear the offspring of another related female or subset of females. These nonreproducing females are known as workers, while those that lay eggs are the queens, and these are distinct castes within the society. In the most primitive eusocial societies, the workers are capable of laying their own eggs but do not do so, opting not to mate and instead work solely in aid of the queen, who is either a sister or their mother. Should the queen be injured or die, any one of the workers might then succeed her as a new queen. The caste distinction is therefore one of behavior, and there is a flexibility to the societal structure. Bumble bee societies are based on this model.
A diversity of Hymenoptera (ants, bees, and wasps) and their nests—from subterranean ants (family Formicidae) in their gallery; to ground-nesting, solitary bees (family Andrenidae) and the cuckoos that prey upon them (family Apidae); to the papered colonies of yellowjackets and the earthen pots of potter wasps (family Vespidae). From Jules Rothschild, ed., Musée entomologique illustré: histoire naturelle iconographique des insectes (1876).
The nest of the buff-tailed bumble bee (Bombus terrestris) consists of a series of simple pots loosely clustered together, some of which are used to store food, while others are the chambers in which larvae develop. From William Jardine, ed., Bees. Comprehending the Uses and Economical Management of the Honey-Bee of Britain and Other Countries . . . (ca. 1846).
Some eusocial societies, however, have caste systems that are more rigidly set in place, with there being considerable anatomical differences between the sterile workers and the queen caste. In this these societies it is not possible for a worker to replace the latter. In fact, some of the most ubiquitous and ecologically dominant of all insects are such highly eusocial species, specifically the triumvirate of termites, ants, and certain species of bees, including honey bees. While all ants and termites are highly eusocial, among bees, social behavior is the exception rather than the rule. Most of the twenty thousand species of bees are solitary, and those that form characteristic eusocial societies represent perhaps no more than 5 percent of this diversity. The eusocial societies of these three insect lineages form a virtual hegemony over our world. They are, however, not the only eusocial groups; there are some eusocial aphids and thrips, and there is even a primitive eusocial species of ambrosia beetle that lives in galleries (tunnels) in the heartwood of eucalyptus trees in southeastern Australia. Outside of the insects, eusociality is rare. It is found in some spiders and snapping shrimps, but in only two other animals; the naked mole rat of the Horn of Africa and southern Africa’s Damara mole rat are the only eusocial vertebrates. Some argue that subsets of human society meet the criteria for eusocial behavior, so we might include ourselves in this distinguished company.
For most of human history, the majority of people lived under the rule of a leader who was typically male—a chieftain, a king, or an emperor—one whose will, whether it was just, wise, or even deranged, would determine the fates of all others. Communities of social insects were miniaturized versions of our own civilization in the minds of early naturalists, and it is reasonable that they assumed the toiling laborers of insects were male and that the monarch over these workers must be a king.
In 1586, Spanish apiculturist and author Luis Méndez de Torres first speculated that in bee colonies, the insect king was in fact a queen. Two decades later, the father of modern beekeeping, English vicar Charles Butler (1560–1647) published his seminal work on the honey bee, entitled The Feminine Monarchie (1609) (see pages 163-165). Jan Swammerdam (see pages 82-83) would confirm the female gender of the bee monarch through his microscopic study of apian dissections in the 1670s, demonstrating that the “king” bee had ovaries and therefore must be female. The workers, too, proved to be female, showing that bee societies are dominated and run by females, while males serve only to fertilize the queen. Despite finally giving the queen proper credit for her gender, a prior notion that she never mated still persisted. Swammerdam insisted that the male impregnated the queen by some means of seminal spirit, which he called the aura seminalis, but was incapable of actually copulating. It took the keen observations of the Swiss naturalist François Huber (1750–1831) to put this pernicious rumor to bed in his book Nouvelles observations sur les abeilles (New Observations on Bees) (1792). Huber’s “observations” are particularly remarkable when one considers that he was totally blind. Through careful experiments outlined by Huber and executed for him by his wife, Marie-Aimée Lullin (1751–1822), and his manservent, François Burnens, Huber confirmed that a single queen reigns over the hive, that she lays all of the eggs, and that she most certainly indeed does mate with a male. Huber’s book would become the standard reference on honey bee natural history and beekeeping for a generation, and the glass-paneled observation hive he devised revolutionized apiculture.
The three castes of two highly eusocial wasps: the European hornet (Vespa crabro) and the European paper wasp (Polistes gallicus). From Amédée Louis Michel Lepeletier, comte de Saint Fargeau, Histoire naturelle des insects (1836–1846).
The title page to François Huber’s Nouvelles observations sur les abeilles (1792), whereby he presented an account of his studies on the natural history of the honey bee (Apis mellifera) although he was completely blind.
The two most iconic groups of social insects—ants (family Formicidae) and the European honey bee (Apis mellifera)—and their three castes: queens, sterile female workers, and males (dubbed “drones” among honey bees). From Lepeletier, Histoire naturelle des insects.
The males of eusocial bees are known as drones. Butler correctly realized that the drones were male, but he assumed they mated with the workers. The drones of honey bees are unique among bees in that they die after copulation; the male organ and viscera are ripped off as the drone disengages from the queen. Fortunately the males of other bee species do not suffer such fates. In termite colonies, the reproductive male (there is only one) at least gets the royal title of king, although his only functions in termite society are to act as consort to the queen and release pheromones that help control the other castes in the colony (the queen does this as well). In particular, if a queen dies, then the king emits pheromones that induce the development of replacement queens. Male ants are not so fortunate as to receive a specialized name, perhaps because they do not live long after completing their singular duty to their monarch.
Insectan caste systems are not always binary, consisting of only workers and queens. Some insect societies have a third caste, the soldier caste, which serves the function of protecting the colony. Soldier castes can be found in aphids, thrips, some ants, and termites (see pages 70 and page 74). Soldiers are specialized females that, like the workers, do not reproduce but are anatomically modified for defense. Soldiers have evolved any number of medieval means by which to engage and defeat invaders. At their simplest, many have massive heads and muscles supporting elongate snapping jaws, but others are far more creative. The soldiers of nasute termites (from the subfamily Nasutitermitinae), for example, have heads that are modified into something resembling a squeeze bottle, complete with a forward-directed spout known as a nasus (from the Latin for “nose,” and by extension, a nozzle or spout). Such soldiers spray an aerosol chemical from the spout, either as a repellant or as a glue that ensnares the attackers, which are usually ants. Soldiers are often so highly specialized as to no longer be capable of feeding themselves, relying instead on workers to nourish them.
The first animals to evolve complex societies were the termites, having done so by the late Jurassic, or at least 145 million years ago, a time in which Stegosaurus, Apatosaurus, and Allosaurus roamed over Colorado and Wyoming, pterodactyls soared overhead, and birdlike Archaeopteryx lived in Germany. The societies of ants and bees similarly appeared alongside dinosaurs, out-surviving the latter with the exception of dinosaurs’ feathered descendants, birds. By the time our species appeared approximately 300,000 years ago, the civilizations and cities of termites, ants, and bees had surrounded the globe and survived cataclysms of global intensity. Despite the success and hardiness of these societies, it is sobering to watch how vulnerable they have been to the effects of human-induced climate change and habitat destruction. For example, bumble bees, which are some of our most vital pollinators, are disappearing from many places where they were once abundant.
INSECT ARCHITECTURE
A prerequisite for being social is, of course, a common structure within which to live. However, not all animal architecture is associated with social behavior. In the insect world, the most basic constructions are simple roosts in which a mother rears her offspring. By example, female earwigs will occupy small spaces, ranging from simple burrows in soil to crevices under bark or stones, within which she will tend to her younglings. Solitary wasps and bees dig burrows in which they place collected provisions and lay their eggs, and caddisfly larvae build cases for retreat. Protective cases among solitary insects are familiar—and frustrating—to many homeowners with yards; particularly those of us who have had to pull bags woven from plant materials and silk by bagworms—the caterpillars of moths in the family Psychidae—from our ornamentals. Nonetheless, the constructions of the eusocial insect species are particularly magnificent and have inspired imaginations since antiquity.
The most familiar eusocial construction is the hexagonal comb of a honey bee. There are seven species of honey bees, all of which construct waxen combs of six-sided cells. Within these cells the bees store honey and rear their larvae. For most honey bee species the combs are built within the confines of some cavity, such as a hollow in a tree. The combs hang vertically, and the workers walk about the outer surface, forming a constantly moving curtain of living insects that help to protect and regulate the combs. The bees are remarkably adept at maintaining a constant temperature within the hive, making certain that conditions remain ideal for the developing brood as well as for the preservation of the communities’ stores. Bees can warm the hive by contracting the muscles that move their wings, but while holding their wings in place. This movement generates a great deal of heat as the energy is not released by flight. Bees can also fan their wings to move air and cool the enclosure during particularly hot days.
There is perhaps no architectural feature more recognizable than the waxen hexagonal combs of honey bees (species of the genus Apis). The combs of the domesticated European honey bee (Apis mellifera) can be easily manipulated within wooden frames, making modern-day beekeeping a profitable enterprise. From Lepeletier, Histoire naturelle des insects.
Bumble bees are also eusocial, albeit of the more primitive form, whereby workers are capable of succeeding their queen should the need arise. Bumble bee nests are also found within cavities, and the bees tend to use the abandoned burrows of rodents or birds, nestled amid or under vegetation. The bees construct waxen pots that are grouped into irregular, horizontal clumps. Some pots are used for developing larvae, while others store pollen. Other primitively eusocial bees dig multibranched burrows within the soil, such as the social species of sweat bees. Yet other lineages of primitively eusocial bees, such as allodapine bees, relatives of the more familiar carpenter bees, will excavate burrow within hollow stems.
Like their cousins the bees, stinging wasps such as paper wasps, hornets, and yellow jackets also build elaborate nests, replete with rows of cells. Some nests are dug into cavities within the ground, but the more conspicuous nests dangle from eaves, wrap around branches, or are delicately suspended by slender stalks. While some nests are open, exposing the papery combs—usually with many females covering them and at guard—others are securely encased by papery or hard mud overlays. Wasp colonies can become massive, and one interconnected series of paper wasp combs suspended from the roof of a cave in Brazil was discovered to consist of millions of individual wasps. Those species with smaller colony sizes, or even wasps who are solitary, also build delicate nests, some using leaves as anchors or curling them to form parts of the architecture itself.
Diverse stinging wasps (families Vespidae, Tiphiidae, and Pompilidae) from Madagascar are depicted in Henri de Saussure’s volume Histoire physique, naturelle et politique de Madagascar, Orthoptères (1895). The illustration includes the delicate comb of the social paper wasp (Ropalidia bicincta), which is suspended by a fine petiole (leaf stalk) from the undersurface of leaves.
A woodcut from Ulisse Aldrovandi’s De Animalibus Insectis Libri Septem (1638 [1602]), depicting the paper nest of the common European wasp, or yellowjacket, (Vespula vulgaris).
ANTS AND TERMITES
Like bees, ants and termites are also excellent architects, and in many ways their constructions make honeycombs seem trivial in comparison. While many bee nests are distinctive for their uniform structure, those of ants and termites stand out for their irregularity. Most ant and termite nests are built within different substrates, such as wood or soil. They typically consist of chambers connected by networks of tunnels and have one or more openings to the outside world. Many of these nests are underground and usually go unnoticed by humans, although the galleries that are dug can be intricate.
Thick layers of paper envelopes (made from masticated wood fibers) encapsulate intricate layers of combs within the social nests of the common European wasp. The largest of these nests can house upward of four thousand workers, tending a brood of over fivem thousand larvae during a cycle. From Lepeletier, Histoire naturelle des insects.
The soil excavated by the ants building subterranean nests is brought to the surface and dumped, resulting in small mounds, much like chat piles from human mining activities. These colonies can dig quite deep, with those of some ant species extending to depths of 12 feet (3.66 meters) or more. While it may seem simple to dig tunnels and chambers, these nests are well planned. At their most complex, they include ventilation mechanisms for circulating air and drainage tunnels for funneling water and wastes away from those chambers serving as nurseries, granaries, or gardens. As with bees hives, the temperatures within can be controlled with great precision. The mounds created by wood ants are particularly familiar sights in forests in North America and Europe. These can be massive, with the largest approaching nearly four hundred thousand workers and forming small mountains exceeding the height of an average man. There are usually small earthen craters at the cores, but otherwise the mounds are built up from twigs or needles from trees. Other ants build their nests in trees, constructing them of twigs, leaves, and other plant materials that they weave together into suitable cities for their colony.
Perhaps the most impressive and easily observed nests are those of macrotermitine termites, a lineage found only in the Old World, whose often colossal nests can define and transform vast landscapes in Africa. At their core, the principal galleries are subterranean or at the surrounding soil level, with a broad cellar from which extends small channels up to and opening on the sides of the mound. These termites cultivate fungi within specialized garden chambers that are situated above the subterranean network of galleries. The mound itself is built of clay moistened by the termites’ saliva, which cements the structure. Cemented is an apt term, as the mounds are extremely sturdy and not easily breached. It often takes a heavy pickax wielded by a particularly strong person in order to make a significant dent. The mounds are porous and have series of chimneys that extend throughout to help regulate airflow as well as control the temperature and humidity within.
Social insects represented by workers and a winged male of various species of Malagasy ants (family Formicidae) from A. Forel’s 1891 contribution to the Histoire physique, naturelle et politique de Madagascar.
The arboreal nest of the Malagasy acrobat ant (Crematogaster ranavalonae), built up of twigs and leaves and bound together in a carton composed of chewed plant material mixed with soil, which hardens into an impenetrable wall. From A. Forel, Histoire physique, naturelle et politique de Madagascar.
An exquisitely rendered lithograph of a nest of the Bornean termite Dicuspiditermes nemorosus, a species first discovered by George Haviland, who made a detailed account of their elaborate nests. From “Observations on Termites…,” The Journal of the Linnean Society of London. Zoology. 1898.
While some macrotermitine nests really are mound-shaped, others extend upward like blades, broad but thin. The blade-shaped nests are built such that their broad surface is oriented to the sun, catching the rays of first light to help warm the colony after a cold night. Looking across an African savannah, one can find the landscape studded with dozens of such colonies. The heights attained by these nests are impressive, and are large enough that elephants will use older mounds to scratch themselves. To put this achievement into perspective, consider the current tallest building in the world, the Burj Khalifa of Dubai. This impressive tower extends a staggering 2,722 feet (829.7 meters) into the sky, a little over one-half of a mile, with 163 individual stories above ground topped by a massive spire. The average height of a Western male is generally 5 feet 9 inches (1.75 meters), meaning that at our current best, humans have built a structure approximately 473 times our size. This is trivial compared to what insects can achieve. In the largest termite species, Africa’s Macrotermes bellicosus, the average worker—the caste that labors to build their colossal structures—is 0.14 inches (3.6 millimeters) in length, and some build nests that extend 27 feet (8.2 meters) into the air. The termite mound is therefore about 2,286 times the size of the workers. This is a conservative minimum value, as many workers are even smaller—and their towers do not include spires with unusable space. Were we to build today something of equivalent proportion, the building would have to be at least 13,147 feet high, or 2.49 miles, and consist of no less than 1,314 stories!
SQUATTERS AND FARMERS
The nests of social insects house entire industries of other insects, all eager to benefit from the protective enclosure and concentration of resources residing therein. These insect squatters, called inquilines, include mites, true bugs, and a spectacularly diverse fauna of specialized rove beetles. Inquilines use all kinds of means to gain access to nests and remain undetected once inside. Some, like termite bugs, are flat with textured backs meant to mimic the walls of termite tunnels, thereby camouflaging themselves by pressing tightly against the tunnel walls. Rove beetles not only at times mimic their hosts—such as those who resemble ants—but are also excellent chemists, secreting scents identical to those of the ants and termites with whom they live. They will even copy the behaviors of their hosts, all so they might move about the colony without raising alarm.
The remarkable architectural achievements of the mound-building termites of western Africa Macrotermes bellicosus were initially made known to European scholars though an eloquent letter from English naturalist Henry Smeathman to the famed explorer Sir Joseph Banks, who published the missive Some Account of the Termites Which Are Found in Africa and Other Hot Climates in 1781.
While we like to think ourselves clever for having developed crop species and domesticated livestock, social insects evolved agriculture and animal husbandry eons before we did so in the Neolithic. Ants, termites, and beetles have each evolved agricultural systems, cultivating crops of fungi from which they derive their nourishment. Unlike us, for millions of years these insects have practiced sustainable agriculture, while we struggle to adopt such methods in the cultivation of our crops. There are, however, some forms of insect agriculture that do cause damage to the environs while they go about their cultivation.
Ambrosia beetles live in galleries dug through living trees, and they inoculate the walls of their tunnels with a fungus that infests the surrounding wood. As the fungus grows, the beetles feed upon it. Newly dispersing beetles then take samplings of the fungi with them when they found new galleries. The infamous mountain pine beetle (Dendroctonus ponderosae)presently devastating forests in Canada and the western United States, is an ambrosia beetle that introduces a blue stain fungus, Grosmannia clavigera, to pine trees. The fungus not only serves as a source of food for the beetle but also inhibits the natural defenses of the trees, such that they do not exude resin. The burrowing beetle larvae ultimately circumnavigate the tree, cutting off its internal water flow, and together the beetles and fungi leave their host dead.
In a manner more similar to human farmers, fungus-growing termites and ants cultivate actual gardens, grown within specialized chambers deep within their nests. While fungus-growing ants are restricted to the New World, farming termites are only found in the Old World, so the two groups do not ever overlap. Fungus-growing termites usually cultivate their crops on beds of dead plant tissue or animal feces. The fungus produces nodules that are then collected and consumed by the termites. New queens who found new colonies must locate a starting sample of the fungus in the surrounding environment. This is easily done by collecting spores that are emitted from mushrooms sprouting from the sides of older termite mounds.
LIFE AND DEATH IN ARABIA FELIX
While Carl Linnaeus’s name is synonymous with biological classification, his contributions went well beyond his writings. He was also a gifted professor, giving popular lectures at Uppsala University and organizing botanical excursions that attracted many. Some of Linnaeus’s most promising students undertook voyages of exploration in order to bring botanical and other biological specimens back to Uppsala, so that a fuller picture of God’s grand design might be understood. These adventurous students became known as Linnaeus’s “apostles,” and as journeys to exotic locales in the eighteenth century were often fraught with peril, it is perhaps unsurprising that not all survived their ordeals. One of these intrepid young men was Peter Forsskål (1732–1763), a free-thinking Swede who had earlier written the tract Tankar om borgerliga friheten (Thoughts on Civil Liberty) (1759), which included, among other things, heretical notions such as freedom of speech; it was a virtual blueprint of the United States’ Bill of Rights, which would appear several decades later.
In 1760, Forsskål was assigned to join an expedition, launched by the Danish king Frederick V (r. 1746–1766), to Arabia Felix, the southwestern portion of the Arabian Peninsula that today encompasses southern Saudi Arabia and Yemen. Arabia Felix included the fabled kingdom of Sheba, and one goal of the expedition was to bring back ancient copies of biblical scriptures that were presumed to be there for the taking. Aside from Forsskål, the group consisted of the Danish philologist Frederik C. von Haven (1728–1763), German artist Georg W. Bauernfeind (1728–1763), Danish physician Christian C. Kramer (1732–1763), Lars Berggren as man-servant, and Carsten Niebuhr (1733–1815), a German of humble background relative to his compatriots but who was a skilled mathematician and cartographer.
A map of Arabia Felix by Carsten Niebuhr, the frontispiece to Peter Forsskål’s posthumously published work Flora Aegyptiaco-Arabica (1775). Forsskål, the devoted student of Linnaeus, did not survive the ordeals of his expedition, and it was left to Carsten Niebuhr to publish his friend’s copious manuscript notes in several volumes.
The team left from Copenhagen in January 1761, venturing first to Constantinople and Alexandria, then Cairo, and ultimately arriving in Arabia in 1762. The greatest danger they had endured en route was one another—tensions were high among the multinational crewmembers, and at times the atmosphere even became rife with fears of suspected plots of subterfuge. The danger from marauding tribes and deceitful scoundrels as well as the hardship of travel in a hot and arid land eventually melded most of them together as dear friends. By Cairo, all but von Haven had adopted Arab dress and methods of living, knowing that becoming one with their environment and building compassionate friendships with their hosts was critical to the survival of all.
Throughout their journey, Forsskål made collections of plants and animals, preparing copious notes to be shared with Linnaeus upon his return. They were also to serve as the foundation for a grand treatment of the Arabian and Egyptian biotas. Unfortunately, the expedition was plagued by many misfortunes. The group finally reached Yemen on December 29, 1762, but sadly, five months later, von Haven succumbed to malaria. He was followed in death by the hopeful Forsskål in July 1763, who also had contracted the disease. Niebuhr and the others buried him outside of a small montane town near Sana’a where he had passed. The remaining explorers made their way back to the coast, each falling ill. They eventually found passage on an English vessel bound for India, but while traversing the Indian Ocean, both Bauernfeind and Berggren perished of the disease, their bodies committed to the depths. In Bombay, Kramer died, and so by February 1764, Niebuhr was the only one who remained.
The title page to Peter Forsskål’s posthumously published work on the animals discovered during his travels through Egypt and Arabia, Descriptiones Animalium, Avium, Amphibiorum, Piscium, Insectorum, Vermium (1775).
Niebuhr slowly made his way back to Europe, traveling by ship to Oman and then to Persia, along the way visiting the ruins of ancient Persepolis—one of the first Europeans to see the city and, in fact, the first to prepare detailed accounts of its monuments and cuneiform writing. By way of today’s Iraq, Syria, and Turkey, Niebuhr finally reached Constantinople once again in January 1767, and by November of that year he arrived safely in Copenhagen, where the whole expedition had begun six years earlier. He wrote an account of the expedition, and so as to not see the labors of his dear friend Forsskål perish, he published what remained of Forsskål’s monographs on the flora and fauna of the Red Sea environs of Egypt and Arabia.
The title page to the atlas volume of Descriptiones, containing the various images of the plants and animals discovered during Forsskål’s exploration of Egypt and Arabia.
Forsskål discussed twenty-five insect species, including one he called Gryllus gregarius, and that we today know as the voracious desert locust (Schistocerca gregaria), the scourge of biblical plagues. He also described and depicted a soldier and worker of the subterranean termite Reticulitermes lucifugus (called Termes arda by Forsskål) as well as one of their constructed tunnels; the species is notorious for its damage to human structures throughout the Middle East and Europe. These are among the earliest images of the castes of termites. Forsskål’s account also included one mosquito, Culex molestus (today known as Culex pipiens form molestus), so called because of the incessant botheration it makes of itself. While it is not a species that transmits malaria, it is chilling to think of how its brethren helped bring to ruin the journey of Linnaeus’s pupil and his companions.
Forsskål’s work included the first figures of the social castes of termites, showing workers and soldiers of the subterranean termite Reticulitermes lucifugus, as well as portions of their nest constructions. This illustration also included other arthropods he discovered, such as the spider Argiope sector and the thread-winged lacewing Halter halterata.
The most adept insect farmers, however, are ants. Fungus-growing ants have perfected gardening and have been at this activity for at least the last fifty million years. Unlike the termites, ants harvest clippings of leaves upon which to grow their fungus, and queens founding new colonies carry with them a culture of the fungi used to develop a new garden. Like human farmers, the insects face challenges with maintaining a suitable climate and avoiding crop pests, the latter being other fungi or bacteria that may devastate their gardens. To avoid introducing any unexpected “pests” into their gardens, the ants groom themselves and clean their gardens constantly, and some cultivate specific bacteria and yeasts that act as antibiotics, functioning like “weed killers,” to keep the gardens healthy.
Other groups of ants have also evolved to tend plant-sucking aphids or treehoppers, collecting “honeydew” from them. Aphids suck sugary fluids from their plant hosts, consuming massive volumes from the plant in order to gain sufficient nutrition. This heavy flow through their bodies produces considerable fluid wastes; they excrete droplets of this honeydew, which is rich in sugars, much like nectar, and it is therefore desirable to the ants. The ants have evolved to become ranchers, looking over a herd of aphids like tiny cattle. Some ants will even “milk” the aphids like dairy cows, stimulating the aphid to secrete drops of honeydew on command through a stroke of the ant’s antennae. The aphids are protected by the ants, and the ants feed on the honeydew, representing an ideal mutualism. Like human ranchers, should a “field” become used up, the ants will carry their herd to a new location where “grazing” is more suitable. The ants even collect the aphids’ eggs and bring them within their nests during winter months, protecting them from the harsh cold. They then carry the aphid nymphs out to feed once spring arrives.
A diversity of ants (family Formicidae)—queen, workers, and males. Ants are among the most familiar of social insects, living in highly integrated societies throughout the world. From Georges Cuvier, Le règne animal distribué d’après son organisation (1836–1849).
Detail of a dwarf honey bee (Apis florea) comb, with (left to right) drone, queen, and worker above and a sole worker on the comb itself. At bottom right, a worker of the giant honey bee (Apis dorsata). From Charles Horne and Frederick Smith, “Notes on the Habits of Some Hymenopterous Insects…,” Transactions of the Zoological Society of London, 1870.