Once I became a father, I started noticing insects (or “itty bugs,” as Josephine called them), because I was spending a lot more time close to the ground. Moving your face into close proximity with the earth is the key to knowing insects, says Brian Fisher, an ant specialist at the California Academy of Sciences. “You have to go outside, just get a quarter of an inch above the ground, and watch them,” he said. “And you’ll see a whole new world opening up. This small world of insects is actually what’s holding our society together.”
This isn’t hyperbole. E. O. Wilson, the patriarch of ant science, has said that insects are so important that if all the land arthropods disappeared, humans wouldn’t be able to survive for more than a few days. But we are mostly unaware of the ways in which insects support us, not to mention all the cool stuff they do.
No matter where you are right now, if you walk outside looking for wildlife, the first animal you’ll find is likely to be an insect, perhaps an ant. Ants are everywhere, in such abundance that we tune them out like we tune out traffic noise. Lean on a tree for a while and, whether you are in Cincinnati or Kamchatka, eventually you’ll catch yourself brushing an ant off your hand. Get down on your haunches to examine any patch of lawn, or woods, or pavement, and sooner or later you’ll find ants. Scientists doing back-of-the-napkin math have estimated that the total weight of ants is about equal to the total weight of humanity.
When I started trying to gain some familiarity and sense of neighborly understanding with my local ants, I hit a barrier that I hadn’t encountered before: too much information. I could handle pigeons or ginkgos because that was only one species at a time. When I began looking at the handful of common squirrel species, I just had to be careful I wasn’t mixing up a quirk of an eastern gray with that of a fox squirrel. But ants contain swarming multitudes. A researcher in 2003 tallied the number of ant species at 11,006. Five years later, another scientist updated the count to 12,467. We know a lot about just a few of these species, and almost nothing about the rest of them. Furthermore, scientists estimate that there are another ten thousand ant species waiting to be discovered. Anyone who wants to learn about these most common of insects faces a high hurdle: There are libraries full of information about ants, and yet that’s barely the beginning of what there is to learn.
The vastness of the world of ants is an impediment for beginners, but it’s also an enticement: It means that the unknown is waiting right there in the park and in the driveway, ripe for discovery. This quotidian exploration doesn’t seem as exciting as trekking through jungles and seeking hidden empires, but people who have had the full range of these experiences say they are much more similar than you’d expect.
As a kid, scientist Rob Dunn dreamed of journeying into the unknown, and as a biologist, he’s actually gotten to do that. He has explored tropical forests and discovered things previously unknown to science. Having experienced all that, however, he reports that he now finds backyards even more fantastical. “New species, and even whole societies remain to be studied in the dirt beneath our feet,” Dunn wrote. “Among the least explored empires are those of the ants.”
The first step, I figured, was to make out what type of ants I was dealing with. Scientists at North Carolina State University (NCSU)—where Dunn works—have set up a citizen-science project to identify ants around the United States (schoolofants. org). Its protocol is simple: Break cookies (pecan sandies; I’d learn why later) onto index cards, leave them outside for an hour, then dump all the ants that have accumulated on the cards into bags and send them off to NCSU for identification. I couldn’t find index cards, so Josephine and I cut notebook paper into three-by-five-inch pieces. Using markers, we labeled four “green” and four “paved,” then set out the bait. Josephine intently crumbled the cookies onto the cards. She had never had pecan sandies, and decided that they were strictly for ants. I did my best to preserve that illusion. It seemed like a winning strategy until Josephine told me she’d dumped the entire box of cookies outside, to facilitate our collection.
We waited exactly one hour, then went to check the bait. There was an acute absence of ants and the cookies were undisturbed, except for the mound of crumbs on one card: Those had disappeared entirely and the paper was standing on end across the yard. “Maybe the squirrel ate it,” Josephine speculated. Then she confirmed, “Yes. It did.”
This, it seemed to me, was an illustration in miniature of how we humans deal with mystery: We take the limited set of characters and causes we already know (ants, squirrels, cookies) and spin stories around them, until storytelling slips into certainty.
We aren’t overwhelmed by ants in my part of the world, but I was surprised that we didn’t catch any. I began to spin my own theories. It had rained heavily the day before—the first real rain after a long drought—and I decided that perhaps the local colonies were too busy with flood repair to send out foragers. This is how we humans deal with mystery.
I would later learn that many ants deal with flooding fairly well. Lots of species can survive submerged for hours; some can even live underwater for days. Species that invest in expansive nests, like harvester ants, do spend time making flood repairs. But others can simply pick up and move when the waters rise.
Often it’s not water, but the lack of it that threatens ants. Their eggs and larvae quickly dry up if the humidity is too low. And yet ants thrive in deserts around the world by gathering dew and extracting moisture from food. Some species balance water droplets on their mandibles and carry them down into their tunnels (the surface tension of a small drop is great enough that it remains intact when suspended across the mouthparts). Diacamma rugosum ants in India build rudimentary mist-harvesting devices by placing feathers around the entrance of their nests.
Ants are bizarrely unlike people, and yet there’s a hint of human behavior at work in ant colonies. They are just strange enough, while also being similar enough, to prick the imagination. This has led thinkers throughout history to compare ants to people. Why aren’t we more like them? Or are we actually more akin to ants than we’d like to believe?
When King Solomon suggested that people should be more like ants, he was making a point about industriousness and self-motivation:
Go to the ant, thou sluggard; consider her ways, and be wise:
Which having no guide, overseer, or ruler,
Provideth her meat in the summer, and gathereth her food in the harvest. (my emphasis)
Ants are kind of amazing in this way if you think about it. They don’t have bosses or leaders, or a corporate structure or hierarchy. They don’t procrastinate. They don’t need deadlines. There is no top-down organization.
And the normal bottom-up drivers of individual behavior—the itch to reproduce and the instinct for self-preservation—don’t provide a tidy explanation for the motivations of ants either. The worker ants are all sterile females that can’t reproduce, and self-preservation obviously isn’t a priority, because they will sacrifice their lives to improve the fitness of the colony. A few workers of a Brazilian species, for instance, doom themselves to certain death each night by staying outside to seal up the entrance to the nest.
What makes an ant go? And what makes its actions contribute to the long-term strength of the colony, when it is neither controlled by a commander nor compelled by selfishness? It’s all very well for Solomon to call me a sluggard and tell me to be more like an industrious ant, but how do I accomplish this when I don’t even know how ants manage it? Corporate leaders and business theorists would love to figure this out. So would anarchists. Peter Kropotkin, the nineteenth-century anarchist philosopher, was fascinated by ants, and entranced by the possibility that humans might emulate them to achieve grand societal goals without leadership. In fact, the mysteries of ant behavior mirror two of the great questions of philosophy: How do we live together, and how do we attain a meaningful life?
Ant behavior starts to make a lot more sense if you think of the ants not as individuals, but as the cells of a body. It’s a metaphorical body—a body politic if you like. But there’s less friction in ant politics than in ours, because every ant in the colony has the same goal: Feed the queen and enable her to reproduce.
The queen is the ant that starts a colony. She lays the eggs that become all the other ants in the colony. Like an organism, the colony behaves as a unitary whole. It changes as it grows and has a clear life cycle. It has attributes of size, behavior, and complexity that are consistent throughout a species. The queen is its reproductive organ, and the workers are the digestive and circulatory systems.
Ants move resources around the colony by transferring food and water from mouth to mouth. Think of the colony’s tunnels as veins and the ants as blood cells running through them. Each ant has a second stomach, which serves as an internal backpack. If an ant needs food, she’ll tap a sister with an antenna, and the other ant will then provide her with a mouthful of pre-chewed snacks.
The queen sometimes lays eggs for food. They aren’t living eggs—they don’t grow into ants—but they are otherwise identical in composition. This egg cannibalism is simply a way to move nutrients around within the colony, just as a cell releases sugar into the bloodstream for use by hungrier cells. When the queen has plenty of nutrients and workers don’t have enough, she can share her surplus by laying these eggs.
A queen can also do the opposite. If she’s lacking in nutrients, she can suck the hemolymph—the ant “blood”—from developing larvae. She makes a small incision that heals quickly, and the young seem none the worse for it.
Thinking of a colony as a single organism can explain why workers do labor and sacrifice their lives without any possibility of individual reward. What these ants are striving for, from an evolutionary perspective, is to pass on their genes, but by proxy. They can’t give birth, so they rely on the queen, who shares 50 percent of their genes. The only way for a worker ant to increase her reproductive fitness is to improve the fitness of the colony. It’s wrong to suppose they are altruistic. Yes, they work tirelessly and martyr themselves without hesitation, but it’s out of the selfish motivation to perpetuate their colony’s genes.
We have an inkling of what drives individual ants, but this opens a greater mystery: How do these individual actions add up to a colony acting with what looks like an informed strategy? Say I’m an ant going about my daily business, trying to help my colony succeed; what do I do? Should I go out and look for food? Cart larvae around? Dig new tunnels? Start moving the colony to a new location? Go to war? How can a part comprehend the needs of the whole?
Deborah Gordon has been watching harvester ants in Arizona for years, trying to figure this out. She and her students paint the ants with multicolored codes so they can track individuals to see what choices they make. Gordon has found that the ants pay attention to each other and switch tasks based on the chemical signals they pick up from their neighbors. If an ant is struggling to pull a big cricket back to the nest, the nearest ants may smell that struggle and go to help, perhaps releasing chemical “Workers Needed” signals of their own. “The pattern of interactions is the message,” Gordon wrote. From the interplay and spread of individual actions emerges something that looks like intelligence.
The idea of emergent intelligence is wonderfully spooky. But we shouldn’t glamorize it. This system is inefficient: Gordon found that large numbers of ants seem to do nothing all day. And if you’ve ever watched ants, you’ve seen them working at cross-purposes. That worker you recruited to help you pull that grasshopper may start pulling it in the opposite direction.
Of course, in human politics, people are always pulling in opposite directions. Could Kropotkin have been right? Instead of trying to agree on big societal strategies, which often fail anyway, would it work to simply pay close attention to our neighbors? It’s enticing to think that we might be able to give up election campaigns, political theorists, Federal Reserve members, city planners, military generals, and environmental regulators and instead sense (and fulfill) the needs of society through interactions with our neighbors. This, I suspect, would be an unmitigated disaster, but that doesn’t stop me from envying ants.
Imagine if you lived without conscious strategy or struggle in the assurance that your actions made a meaningful contribution to the commonwealth. What a gift it would be to simply know your place in the world, and to have no desire except to fill that role. Think of what it would be like to do away with all philosophizing and searching for meaning, all restlessness, all self-recrimination, all disappointment and anomie, and instead to simply do what you were meant to do.
And yet, I would object to being reincarnated as an ant. Though I’m constantly plagued by my second-guessing mind, I also find it’s incredibly useful. It (usually) keeps me from being duped. Whereas ants trust and cooperate, humans search for ulterior motives. Self-doubt is a burden, but the task of doubting others, the work of skepticism, investigation, and critical analysis brings me great satisfaction. My doubting, self-sabotaging mind is a pain in the neck, but it’s also, well, me.
The robotic quality of ant behavior—their ability to satisfy the needs of their colony without self-interest or apparent self-doubt—makes them perfect targets for con artists. Ants recognize their sisters by scent, but they don’t seem to distinguish between individuals. So, with just the right perfume, various species—beetles, mites, wasps, millipedes, flies, and others—are able to slip into the colony undetected. There is a rove beetle that uses a series of chemical signals to convince ants that it is a foundling infant somehow misplaced from the nursery. The ants carry the beetle home to the brood chamber, groom it, and feed it when it begs for food. This attentive care isn’t quite enough, however: The beetles also eat some of the ant larvae and eggs.
The rove beetle is just one of hundreds of species of ant parasites. As ant scientists E. O. Wilson and Burt Hölldobler put it in Journey to the Ants, “It is as though a human family were to invite gigantic lobsters, midget tortoises, and similar monsters to dinner, and never notice the difference.”
Ants can also be parasites themselves. Amazon ants, Polyergus breviceps, which live all around the Northern Hemisphere, hack into the simple information-sharing systems of other ant colonies to enslave them. To start a colony, an Amazon queen finds a nest of Formica ants and battles her way to the royal chamber. Howard Topoff, at the Arizona Museum of Natural History, had watched these heists and described them in an article for Scientific American.
In most cases the Polyergus queen quickly detects the entrance and erupts into a frenzy of ruthless activity. She bolts straight for the Formica queen, literally pushing aside any Formica workers that attempt to grab and bite her, . . . using her powerful mandibles for biting her attackers and a repellant pheromone from her Dufour’s gland in her abdomen. With the workers’ opposition liquidated, the Polyergus queen grabs the Formica queen and bites her head, thorax and abdomen for an unrelenting twenty-five minutes. Between bouts of biting she uses her extruded tongue to lick the wounded parts of the dying victim. Within seconds of the host queen’s death the nest undergoes a most remarkable transformation. The Formica workers behave as if sedated. They calmly approach the Polyergus queen and start grooming her—just as they did their own queen. The Polyergus queen, in turn, assembles the scattered Formica pupae into a neat pile and stands triumphally on top of it. At this point, the colony takeover is a done deal.
While the colony she has usurped feeds her, the Polyergus queen begins laying her own eggs. Eventually the Polyergus army rises up, supported by the Formica slaves. This army will, of course, eventually run out of slaves, because, without a queen, the stock of Formica workers will not be replenished. It is a crisis because Polyergus cannot survive without slaves. They cannot dig tunnels, or care for the young in the nursery. Amazon ants are slavers through and through, so dependent on this way of life that they no longer recognize food they pass on the ground: They only eat what slaves have chewed for them.
Ants have an amazing armamentarium. Amazon ants make their raids using chemical propaganda signals, sending their victims dashing about aimlessly while they move in. A Malaysian Camponotus species can become a suicide bomber, blowing itself up and splattering all around it with green venom. Pachycondyla tridentata has a poisonous sting for big adversaries and the ability to produce sticky foam to bog down smaller attackers. Others are covered in spiked armor.
It’s not all violence among ants. There are species that can work together, like carpenter and acrobat ants. These two share a nest and cooperatively maintain gardens high up in trees. There are beggar ants that subsist entirely on the rubbish from another species’ nest. There are thief ants that live by stealing food from others. Even when ants have a direct confrontation, they generally try to avoid carnage. When two ants meet, they will touch antennae, reading the scent conveyed by the pattern of molecules on the other ant like a bar code. If it turns out that they are from different colonies, they try to avoid a fight through ritualized posturing: They open their mandibles as wide as possible, rear up on their back legs, and lift their abdomens threateningly. Often one ant will back down, averting violence.
Ants communicate primarily via scents. Every ant is coated in a layer of waxy hydrocarbons that volatilize, giving off the unique smell of the tribe. Ants also have a collection of glands spread throughout their bodies that contain ten to twenty chemicals. These are mixed in different proportions to convey different messages. E. O. Wilson and others dissecting ants under microscopes have been able to separate the chemical organs. Wilson found that when he wrote his name using the invisible fluid from one gland as ink, the ants followed the trail, making his signature visible with their bodies. When another of the chemicals was applied to an ant, her family became convinced that she was dead and deposited her in the trash heap; when she crawled away, they forcefully returned her to this cemetery.
Gordon says these experiments only give us the faintest understanding of chemical ant language. The meaning of each scent depends on its intensity, its combination with other chemicals, and the context: A smell that means one thing inside the nest might mean something very different in the middle of a battlefield. Exposing ants to chemical scents and trying to learn their meaning by watching the ants’ reactions, she writes, is like an alien trying to learn English by blaring the word “ant” at New York City and watching the human response.
What do these chemical messages smell like? Some chemicals don’t register in the scent receptors in our noses, or they exist in such tiny quantities that we can’t pick them up. But ant scientists tell me that all these chemicals together give some species a signature smell. Most ants carry the vinegary scent of formic acid, and some species smell strongly of citronella. If you crush just the heads of ants in the genus Odontomachus, they smell like chocolate. Weaver ants smell and taste like limes (it’s always worth tasting ants), and army ants smell like rotting meat or burnt hair. The chemical that gives odorous house ants their smell is nearly identical to the chemical that makes blue cheese stinky.
Two weeks after our failed experiment as citizen-scientist ant collectors, we tried again. This time I was pickier about the locations. Instead of dropping the cards at random, I put them in spots where I’d seen ants before. There’s a piece of pressure-treated wood separating the grass from a row of ferns and camellias running along our fence, and as I peered down at this board I saw an ant walking purposefully forward. Another came toward it from the opposite direction. When they met they paused, tapped each other with their antennae, then continued on their way. I had found a trail. I set my index card squarely across this line of movement, put a quarter of a cookie atop it, and then sprinkled the crumbs stuck to my fingertips all around it.
Half an hour later, Josephine and I went back to check our bait. Not an ant in sight.
“Let’s just watch this one on the board for a while,” I told Josephine. I sat down cross-legged on the grass, and she sank into my lap. There were no ants to be seen, but as I scanned the ground, other movements began to pop out at me. A brown beetle about half the size of a three-year-old’s pinky-nail clipping dashed to the curving edge of a brown camellia leaf. It wiggled its long, pennantlike tail.
I pointed. “What do you think that is, Josephine?”
“An orckrises,” she said confidently.
For all I knew, she could have been right. There are some four hundred thousand beetle species, many more than there are of ants. (J. B. S. Haldane, one of the founders of evolutionary biology, joked that if there were a creator that shaped each creature, he must have had an inordinate fondness for beetles.) Perhaps Josephine had just named a new species. Perched on the leaf, it opened its shell, unfurled onionskin wings, and tumbled gracelessly into the grass.
Another beetle, a shiny round fellow, like a ladybug of one-tenth the normal size, trundled along nearby. A tiny, long-armed white spider was performing calisthenics on a dried leaf. A fly of some sort glided by noiselessly. A red spider mite dashed up a blade of grass and ran in circles on a leaf like an overcharged windup toy. A wolf spider of monstrous size compared to these itty bugs surprised us by taking a few steps out of a hiding place under the pressure-treated board. If I were being exhaustive, I could fill a book dedicated solely to the creatures we spied in a square foot of lawn.
Josephine called me back to the task at hand. An ant had ventured onto our index card. It lifted its head high, waving its antennae. Then it made a thorough investigation, touching the cookie from all sides and stopping to inspect the smaller crumbs. It did not pick anything up, and left the way it had come. I expected that this ant was going for reinforcements, but when other ants appeared, they came from another direction, following the trail I’d originally noticed. These ants bumped into crumbs and proceeded hastily around them. It was clear that these ants were not interested in pecan sandies. Perhaps they were some unusual sort of ant, I thought hopefully; perhaps I was about to identify a species that does not love sugar. I’d soon find out that I was wrong about the ants and the cookie’s enticing qualities: They are both sugary and fatty. But this only deepened the mystery: What was this ant that crawled over delicious food without any sign of interest?
Josephine plucked a bud from the camellia bush and peeled back the petals. She’d been quietly absorbed for half an hour—longer than she usually sits still for just about anything, except cartoons. But eventually she got up and wandered off. My own mind meandered. Then I saw it: a dark cluster on a camellia bud. Aphids. And there, sure enough, were three ants standing guard, patrolling their little herd. Perhaps the ants were ignoring my cookies because they were intent upon the aphids. I leapt up and found Beth and Josephine in the living room. “I found what the ants are eating,” I announced. “Come see.”
The aphid-covered bulb was at about Josephine’s eye level. “What’s that—all that black stuff?” She wrinkled her nose. The aphids were so tightly packed they looked like a solid patch of fungus.
“Lots of little bugs,” I said. “Do you see the ants climbing on top of them? They herd the aphids like cows and milk them.”
“Milk them?” Beth said.
“Yeah, the aphids express a sugary liquid called honeydew from the anus.”
“And the ants eat that when they could have pecan sandies?” Beth joked.
I reached into the camellia bush and plucked the twig supporting the blossom. At the first tremor, the guardian ants began running frantically around the cluster of leaves, waving their antennae. They were looking, I suppose, for whatever might have landed to attack their herd. I carried the twig inside and dropped it in an empty strawberry jelly jar.
Insect livestock are the most reliable source of sugar for many ants. Ants most frequently herd insects from the order Hemiptera, of which aphids are one example. They are herbivores that suck the juices from plants and excrete the excess sugars in the honeydew. Some aphids produce their body weight in honeydew every hour, and if ants aren’t harvesting it, the sugar can pile up to such an extent that it makes it worthwhile for people to gather it. According to Wilson and Hölldobler, “The manna ‘given’ to the Israelites in the Old Testament account was almost certainly the excrement of the scale insect Trabutina mannipara, which feeds on tamarisk. The Arabs still gather the material, which they call man.” In Australia, honeydew is called sugar lerp, and one person can collect three pounds of the stuff in a day.
If you turn up your nose at eating excrement, you should know that you may have already done it: A lot of honey comes not from the nectar of flowers, but from this honeydew, which bees collect from leaves. Essentially, this honey is insect poop that’s been processed inside another insect and then vomited up.
There were two ants and several dozen aphids on the camellia bud I’d dropped into my jelly-jar terrarium. One ant ventured out to explore the jar while the other stayed behind. Then they switched roles. I imagined that they were coordinating their efforts so that their flock always had a guard.
I was eager to identify the ants, and optimistic that I would be able to do so. There’s a trove of information online: AntWeb.org, AntWiki.org, and the Encyclopedia of Life (eol.org) all have detailed pictures of just about every known ant. After perusing the well-magnified and perfectly lit creatures pictured by my various guides, I would turn back to the tiny insects dashing around under my magnifying glass and rub my eyes. I had no clue.
One problem was that there are thousands upon thousands of known ant species, and even more unknown species. Trying to find a match was like trying to find an identical grain of sand on a beach. I suspected I had something I hadn’t heard of before, something that might shun cookies.
One of the best tools for identifying any species is a dichotomous key, which provides a series of either-or choices (for example, a dichotomous key for trees starts by asking, “Are you are looking at needles or leaves?”) to lead you down a narrowing path, like the game Twenty Questions, until you reach the correct identification. But there are more than 350 dichotomous keys listed on AntWiki alone. These have titles like: “Key to Myrmica inezae species group.” I needed a dichotomous key to the dichotomous keys!
Another problem was that my ants were so small. From the human perspective, an ant is pretty much just an ant. As soon as you begin to look at ants through a magnifying glass, however, a world of wonderful diversity snaps into focus. With the benefit of magnification, Wilson and Hölldobler write, ants “differ among themselves as much as do elephants, tigers, and mice. In size alone the variation is spectacular. An entire colony of the smallest ants . . . could live comfortably inside the head capsule of a soldier of the largest species, the giant Bornean carpenter ant, Camponotus gigas.”
I’d ordered a hand lens online, a high-quality jeweler’s loupe with tenfold magnification. As luck would have it, it arrived by mail later that afternoon. Using the lens took some getting used to, and I found it was impossible to catch the speedy ants in its narrow field of focus.
Eventually I realized that I’d never be able to identify my ants on the hoof. I plucked one out of the jar—stricken by guilt for a moment for leaving the other ant alone—and dropped it into a pool of rubbing alcohol. It stilled immediately. I fished it out with a pair of tweezers, repositioned my light, and bent over it with my hand lens.
There’s something miraculous about a good magnifying glass. I squinted into a blurry mishmash of color, then pinpointed the correct focal distance and I found myself in a different world. When I’d been watching the insects in the grass with Josephine, I’d fancied it was something like a real-life version of Tolkien’s Mirkwood—a forest filled with monsters. I’d loomed over the forest, separated by my bulk. But by bending light, the hand lens was able to transport me into that world: I was no longer peering down from above, but eyeball to antenna with one of the monsters. The ant was a great sodden beast splayed on an endless plain of woody cells—my bamboo desktop as I’d never seen it before.
The first thing you are supposed to do when trying to identify an ant is to look to see if it has one petiole or two. If you draw an ant, you’ll likely start with three dots: the head, the thorax (the base for its six legs), and the abdomen (also known as the gaster). The petiole is a little lump (or a double lump) at the ant’s waist, between the thorax and abdomen, and it was quite obvious in the photos I’d found online. When I looked through my hand lens, however, the petiole was nowhere to be found. In fact, I wasn’t even sure my ant was right-side up. I took a breath, pulled the light down closer, and slowly began to find my bearings.
It took a good half hour of frustrating concentration and ungainly prodding with the tweezers, which appeared, in this magnified world, like rough-hewn steel girders. There’s a peculiarity of the mind, or at least of mine, that presents tangible resistance to seeing something new. I had no system of categorization or naming to make sense of what I was seeing, and so for the first few minutes I saw nothing but a chaotic jumble of legs and body parts. I would stare at the images on my computer screen, then bend over and search for something similar on my ant. Eventually I found one landmark, then another.
I had thought this ant was black, but actually it was a translucent brown, with a darker, striped abdomen. It was beautiful, actually. I followed the curve of the head, found the antennae mounted about where you’d expect a nose, and to each side a black, multifaceted eye that was perfectly symmetrical, as if shaped by a jeweler from jet. I felt a shiver of delight. The eye of an ant! I’d seen thousands of ants, but until that moment, I hadn’t realized I’d never seen one of their eyes. I felt richer for having seen it.
By nudging the ant’s body to form a curve, I was able to expose the place where the petiole was supposed to be—and yes! There it was, nestled up against the abdomen, and there was very clearly just one. I’d found a simple dichotomous key for California house ants that walked me through a process of elimination starting with the question “One petiole or two?” A few steps later, the guide indicated that I was looking at Linepithema humile. I felt a chill of disappointment. This was not some interesting new species, it was the most common thing possible: an Argentine ant.
Though common, the Argentine ant is also strange. Actually, the thing that makes it common is what makes it so interesting. There is just one species of the Linepithema genus in North America, and for a long time, there was just one colony—one massive imperial family. In most ant species, each colony is independent. Each lives for as long as the queen lives—fifteen, twenty-five years sometimes—then dies. When the queen reaches the end of her life the workers continue collecting food for a while, but the nurseries empty, and eventually there are no workers to replace the fallen. A colony without a queen is like a headless chicken: still running, but going absolutely nowhere.
Argentine ants, in contrast, produce multiple queens that generally stick around the nest. So instead of dying when the queen dies, an Argentine ant colony can grow in sprawling immortality. In a fit of creativity, scientists named the biggest one the Very Large Colony. In the summer of 1998, Neil Tsutsui and Andy Suarez, both grad students at UC San Diego, decided to see how big this Very Large Colony was. They collected some ants around San Diego, put them in jars, and drove north. They knew that ants from a different colony would fight with the ants they were carrying, but all the local ants they put in a jar with the ants they’d brought with them got along happily with the out-of-towners. Tsutsui and Suarez found that there was just one family of Argentine ants from beyond the Mexican border up through California to Ukiah, in Mendocino County. It was a single supercolony six hundred miles long.
That turned out to be just the beginning. On the West Coast, the ants made their way up to Vancouver Island, and scientists began asking, Where else? When they plopped ants from California and Japan in the same jar, the ants again recognized each other as colony mates. Same with ants from the Pacific Islands, Australia, New Zealand, South Africa, and Mediterranean Europe. The sun never sets on the Very Large Colony; it exists anywhere with the Mediterranean climate that Argentine ants love.
Most other species of ant are not as aggressively expansive as the Argentines. Colonies frequently squabble over borders, but manage to live side by side. Even ants that enslave other species don’t entirely wipe out their adversaries. Argentine ants, on the other hand, simply overrun other colonies. They aren’t built for war—they don’t have the fancy weaponry that some other species have—but they are able to overwhelm their competitors by virtue of their numbers and efficiency. They take up all the territory and gobble up all the food. Some ants eat mostly meat, some ants need mostly sugar, but Argentine ants eat everything. As a result, the native ants have been wiped out wherever the Very Large Colony dominates. It wasn’t just chance that my backyard ants were L. humile. In fact, it would have been surprising if I’d found anything else.
Perhaps the greatest advantage held by Argentine ants is that they thrive in the habitats created by modern humans. L. humile comes from the banks of the Rio Paraná, which frequently floods, tossing up massive piles of driftwood and mud, then washing them away just as quickly. The Argentine ants work with this constant change. They might form a nest under a rotting log until that location gets too wet, and then move the larvae uphill, under some leaves. Then they’ll shift the nest yet again to be closer to a delicious rotting fish—all in one day. Urban and suburban lawns are the California versions of the Rio Paraná: landscapes that are regularly flooded by sprinklers, raked clean of leaves and sticks, and shorn of shaggy growth by mowers. Any species that wants to survive in this shifting environment has to be adaptable, and ready to abandon a home at a moment’s notice.
Humans alter the natural landscape by building and gardening, and then Argentine ants move in and alter it still more: They raise herds of aphids and scale insects, which thrive on our rosebushes and fruit trees. They evict native ants, and by extension, native plants like the California bush poppy, which relies on harvester ants to distribute its seeds.
Argentine ants seem inexorable, but they are not on their way to global domination. It’s more likely that we are now watching the decline and fall of their empire. The Very Large Colony is essentially one happy family, but other colonies are following it around the globe, and when these unfamiliar ants meet, they fight. Four colonies of Argentine ants are battling it out in Southern California now, keeping each other in check. And there are multiple colonies all along the Gulf Coast, showing up as far north as New Hampshire on the East Coast (which makes sense, because the bulk of the shipping traffic from Argentina goes to the southeastern United States). It’s only a matter of time until more families of Argentine ants begin competing with the Very Large Colony, or until the colony breaks into warring factions. And then there are challengers among other species of immigrating ants, such as the red imported fire ant, the Asian needle ant, and the crazy ant, each of which appears to be wiping out its predecessors.
Perhaps the most significant threat to the Very Large Colony is its own success. It has created an international group of ants that recognize each other because they are so genetically similar. That lack of diversity is its Achilles’ heel; it makes the entire empire susceptible to the same pathogens. Argentine ants abruptly vanished from a few blocks in the California cities of Riverside, San Diego, and Davis. Perhaps they were wiped out by insecticide treatment, but Philip Ward, a UC Davis ant scientist, favors another hypothesis: “Some pathogen has spread locally, causing population declines, a sort of colony collapse disorder for Argentine ants,” he suggested. In New Zealand, Argentine ants were spreading like a tsunami throughout the 1990s, but by 2011 researchers found that the species had undergone a “catastrophic collapse” and native species were resurgent. Change is the only constant in nature.
The story we generally tell about invasive species is one of domination and extinction. A new species is always an invading army of ruthless totalitarians, replacing diversity and color with uniformity, leaving the world poorer. But this dire vision doesn’t hold up to scrutiny.
Invaders get a lot of attention at first, when they look like they might be an existential threat. But journalists and scientists pay much less attention to what happens once they settle in to an environment. Environmental journalist Fred Pearce noticed that he would write stories about the terror of some new invasive, but then the furor would pass and no one would follow up to see what eventually happened. One of those stories was about a “killer algae,” Caulerpa taxifolia, that was smothering the shores of the French Riviera and spreading through the Mediterranean. But when Pearce went back to check, he learned that soon after his piece was published the algae began to disappear. “They are now virtually gone,” he wrote. “Nobody reported that. Not even scientists.”
Another time, Pearce wrote about the zebra mussel, which overtook the Great Lakes, outcompeting native species for plankton and clogging pipes. People were fascinated by stories of the invasion. But the media wasn’t interested in reporting that zebra mussels were only thriving because the lakes were so polluted. Zebra mussels eat the polluting algae, and in the long run have probably done more good than harm. Pearce writes, “Light penetrating through the water has revived plants on the lake bed, and many fish—like the previously endangered lake sturgeon and smallmouth bass—have done very well by eating zebra mussels.”
“A lot of studies happen when a new species arrives, but people don’t often go back to do follow-ups,” said Eleanor Spicer Rice, a scientist who documented the way Asian needle ants displaced their Argentine ant predecessors in Raleigh, North Carolina. One study provides a snapshot of the disruption, but we often simply don’t know what happens as the flux settles down.
When scientists have gone back to follow up, they have never found that the new arrivals created a single-species wasteland. The native species might not be present in the same abundance, might not be in the same places, but they are there. For instance, a study in 2000 suggested that the number of Blainville’s horned lizards had declined by more than 50 percent in areas dominated by Argentine ants. These California lizards eat ants, but for some reason they don’t thrive on a diet of Argentine ants. But then another study in 2013 found that the lizards were doing all right, and still occupying 75 percent of their 1989 range. Basically, the researchers found them everywhere except the places where people had built houses and shopping centers.
When I first heard about the Argentine ant invasion it sounded like a catastrophe, with them spreading implacably around the world. And they do spread, wiping out other ants and the lizards that eat them, but only within a narrowly defined habitat that allows them to thrive. That habitat just happens to be the one created by human development. Instead of saying that Argentine ants are spreading out of control, it would be more accurate to say they are simply a symptom of our presence.
Immigrant species often do reduce native populations, sometimes significantly. But the ecologist Mark Davis has pointed out that they rarely cause extinctions, and when they do it’s of populations in isolated habitats like lakes or islands. All this mixing may yield more biodiversity by producing more combinations, hybridization, and new species. Centaurea plants introduced into California from Spain have evolved so much in their new habitat that they can no longer reproduce with the old-world species. Is this, asks conservation biologist Chris Thomas, now a California native plant?
And then there are cases in which invasive species have provided food or habitat for threatened natives. The gall wasps, for example, that spread into England with turkey oaks were lifesavers for the native birds of Britain (the young of the birds, affected by climate change, had started hatching before the caterpillars they eat emerged from their pupae). In Puerto Rico, the once-endangered coquí frog has rebounded in new forest habitat made up of nonnative trees.
There’s no doubt that these immigrants change our environment, sometimes drastically. As human movement has stirred the worldwide biological stew, aggressive species have wiped out humble ones that had previously survived in some secluded corner. But nature thrives on change. Disturbance and mixing spur evolution, and scientists are finding many new species and hybrids arising with migration. On balance, it seems, the result of ecological immigration isn’t gray uniformity, but just the opposite: Naturalizing species have given us richer biodiversity.
A month after our pecan sandies adventure, the temperature dropped and the rain began to fall. Argentine ants generally stop foraging when the temperature drops below 41°F, so it was no surprise that they began to forage in the one place where it was still dry and warm—our kitchen. This gave me plenty of time to observe their behavior and look for clues to my mystery (why weren’t they interested in pecan sandies?). The ants came streaming in, hunting out forgotten crumbs in the cupboard, infesting the trash can under the sink, and gorging on the sugar high up on a shelf. Some of my research proved useful during these invasions: Instead sweeping away the ants immediately, I carefully traced their trail to its destination and removed the food source. Then I’d wipe the ants away with a sponge. I felt a little ridiculous as I washed hundreds of crushed bodies off my hands when I recalled that I’d experienced a moral tremor upon drowning a single ant from the camellia.
On several subsequent days I noticed that the ants were nosing around a narrow crack between the butcher-block counter and the cupboard. The crack was just slightly wider than the body of an ant, and I wondered if they might be scouting it out as a new home. Then one night I saw that the countertop was thick with ants, all hurrying toward this crack. Looking closer, I saw that one of the ants was twice the size of the rest. I deftly captured it. Some species of ants produce workers of varying sizes that belong to different castes and can more efficiently perform certain tasks, such as defending the colony, but a quick Internet search confirmed that Argentine ants have only two types: workers and queens. The colony visiting my house was attempting to start a new stronghold inside my kitchen, and I had caught the queen. I sealed up the crack in my counter.
In the weeks that followed I caught half a dozen more queens. I kept one in a jar on my desk in the hope that I might see it lay eggs. But raising tiny pets can be difficult: Beth put that particular ant farm in the dishwasher without noticing there was anything inside.
The ants were implacable. No matter how careful we were to clean up our messes and lock away everything they might like, they always were able to locate some new food source. When we left the house for a week, I hoped we’d come back to discover the discouraged ants had left. Instead, they’d found their way inside a box of spice cookies I’d enclosed in not one, but two plastic bags. At that point, we broke down and bought traps containing ant food spiked with insecticide.
The ants ignored these traps in the same way they had ignored the pecan sandies. For all my research, I still hadn’t figured out why my Argentine ants hadn’t been interested in the cookies. But as I watched them in my kitchen, I saw that the ants would frequently become fixated on one particular food and walk past all others. It was like the movement of a crowd: If a great mass is pushing in one direction, it’s very hard for one member of the crowd to stop it or change its course. The colony’s interest in any particular goal grew organically, I speculated, from an initial discovery at just the right time, when there weren’t other options competing for attention. Putting out the traps was a little like trying to get a convoy of people headed for a concert to take a detour to a baseball game instead.
When I asked Spicer Rice about my theory, she confirmed that I was finally on the right track. A colony will often focus on one thing at a time, she said. If ants are gathering water, they will keep going until a forager tries to put her water in the mouth of an ant in the nest but finds that that ant is already tanked up. The same is true with food. “They go out and get protein until they are full, and then switch and get sugar,” she said.
We kept the kitchen cleaner than we’ve ever managed to before and eventually the ants disappeared. Either they found the traps, or they simply moved back outside after the rains stopped and the ground dried out.
After the Argentine ants disappeared, Beth mentioned that she’d seen another species in our kitchen. I was incredulous. Beth shrugged, “Well, maybe they were queens,” she said. “But they did look different.”
A few days later I spotted one of these ants. It was a bit darker than the Argentines, and its abdomen was big and round; it looked like it had an enormous butt. I nabbed it and dropped it into my specimen jar. But I was busy with other things and forgot about it.
A couple of months later, when I called Spicer Rice to ask about something completely different, she happened to mention that winter ants can live in tandem with Argentine ants. As soon as I hung up the phone, I fished my quarry out of the jar and bent over it with my lens. Again it took me a while to find the correct angle and focus, but when I did, it was clear that my ant had the distinctive hourglass thorax and swollen posterior of a winter ant.
Spicer Rice calls winter ants the white rabbits of the ant world, because they disappear down their holes into another world. Their tunnels may go twelve feet underground, the human equivalent of digging a mile deep. In the spring they disappear down these shafts and wait out the warm season underground. In the temperate Mediterranean climate where I live, Argentine ants dominate for most of the year, but they slow down in the coldest part of winter. Then the winter ants emerge and forage madly for food. As they eat, those already significant posteriors expand like balloons until they are stretched so thin that light passes from one side to the other. Then, their gasters full of fat, they return to the depths and seal the entrance for another year.
In his book Adventures among Ants, the ant scientist Mark Moffett suggests four ways of looking at an ant: as an individual, a selfless suffering drudge (the satirical newspaper The Onion once characterized ant farms as “the fun way to teach your kids to accept their miserable fate stoically”); as a society admirable in its organization; as an organism, a single body of many pieces; and, finally, as a mind, with intelligence arising from a crowd of simple choices.
This last metaphor, the colony as a mind, struck me when I read about research revealing how ants lay down chemical markers at a fork in a path to point their sisters toward the most fruitful direction. Each worker pauses at this decision point to make her sign pointing one way or the other. The following ants reinforce or contradict this sign, so the traffic on the network nimbly adjusts as conditions change. If there is a need for workers to haul a grasshopper home, the signals will point them in that direction. If invaders are approaching, the signals will direct workers more urgently to the battlefront. This fluid processing of complex information with a simple series of either-or decisions is similar to the binary system that drives computer science. And those forking paths aren’t so different from neural pathways in the brain. Humans are more sophisticated thinkers than ant colonies. Then again, sometimes it feels like we would be better off with less sophistication. What is life but a series of trail bifurcations anyway? Perhaps the decisions we agonize over are, in fact, predetermined—the sums of a million individual cellular choices. Our conscious minds assume that we are in control, but often the role of consciousness is simply to justify and explain decisions over which it has no control. Are consciousness and reason just things evolution trumped up to keep us from going insane, a Matrix-style fantasy world that keeps us from recognizing the horrific reality that we have no agency and all the perseverating we do over choices is really just rationalization to convince ourselves that we have free will? Or, to flip the comparison around, could an ant colony develop consciousness? Feelings? Spirituality? Crumble some pecan sandies on a note-card with your daughter and eventually you end up grappling with the basic tenets of philosophy. These are the questions that arise if you spend enough time staring at ants.