Sex on Six Legs Read online

  Natural selection can produce what looks uncannily like intelligent thought or emotion but is no more than the relentless culling of minute variations in genetic makeup, generation after generation, for millions of years. Not only that, but insects too have small personalities, with some showing boldness in new situations and some hanging back with what looks an awful lot like shyness. It's turning out that we haven't cornered the market on individuality, either.

  Insects make us question virtually every assumption we have about what makes humans human. They lay bare the workings of evolution.

  Insects Are a Window

  INSTEAD of a mirror, sometimes insects hold up a window, so that we can see through it and imagine life with different ground rules. Insects wear their skeletons on the outside, and they insouciantly transform from egg to grub to gleaming adult in the space of days. Insects use their antennae to smell and hear in ways we cannot even begin to comprehend, with male moths detecting the odor of a receptive female from a single molecule released miles away. Some bees and butterflies can see in the ultraviolet range, giving them an array of colors we don't have names for. Although, as I discuss in a later chapter, insects can learn more than we have previously given them credit for, they produce their complicated behaviors by and large de novo, without benefit of experience or schooling.

  All of that difference means that we can learn from insects without having to claim kinship so insistently, the way we do with the feathered and furred. As the famous evolutionist Richard Dawkins said in an article about the intelligent design controversy, "Many people cannot bear to think that they are cousins not just of chimpanzees and monkeys, but of tapeworms, spiders, and bacteria." This unwillingness is particularly true for insects; it may seem improbable to imagine oneself related to microbes, but it does not offend. But to me that lack of identification with insects is precisely why we can look to them to gain insight into our own lives—we simply cannot anthropomorphize them into cute caricatures of humans.

  Our inability to identify with insects can thus help keep us—and them—out of trouble, because we do not insist on making them into what they are not. Primates in particular, and especially chimpanzees, seem so much like little people that we almost cannot believe they are animals. When a pet chimp named Travis attacked a woman in Stamford, Connecticut, in 2009, people were shocked, mouthing, as Charles Siebert in the New York Times pointed out, many of the same platitudes as when the proverbially quiet neighbor goes on a murderous rampage. "He seemed so pleasant and mild-mannered." Siebert goes on to note, "There is something about chimpanzees—their tantalizing closeness to us in both appearance and genetic detail—that has always driven human beings to behavioral extremes, actions that reflect a deep discomfort with our own animality, and invariably turn out bad for both us and them."

  We don't have the same problems with insects. They are so hard to anthropomorphize, and yet they still have that superficial similarity to us. They challenge us to find an explanation for a behavior without resorting to human-specific quirks of physiology or genetics. Insects allow us to study phenomena—the effect of personality type on health, say—without the confounding factor of the mechanism behind them. In other words, if being hard-driving makes people and rats more likely to die early, you don't know if it's because of the stress itself or because of a hormone such as cortisol that happens to be linked to stress in both cases. But if being hard-driving kills off both people and ants, there must be something in the stress itself that is responsible, because ants don't have the same hormones, or indeed virtually any of the same mechanisms for getting from the environment to the behavior, that people do.

  I have rarely if ever found insects frightening, at least in the abstract. But I certainly find them unsettling, reminders of another world. I am in good company; Charles Darwin, in his recounting of his observations of tropical insects, found that the possibility of finding so many different species "is sufficient to disturb the composure of an entomologist's mind, to look forward to the future dimensions of a complete catalogue." Some of that is the lack of expression, of what the psychologists call affect, the outward manifestation of one's inner being. The great entomologist Vincent Dethier, who wrote eloquently about the smallest details of fly behavior, felt that the lack of expression in insects stood in the way of our empathy with them: "One empathizes less, if at all," he said, "with a beetle or a fly which has a comparatively immobile head than with a praying mantis that turns her head and stares at one." That lack of empathy is not a hindrance, at least in my mind, but a help. Dethier also said, "It may be, as Alexander Pope averred, that the proper study of mankind is man; nevertheless, to know in which respects a fly is not a man cannot help but reveal something about ourselves." The newest discoveries about personalities in insects are revealing that connection.

  Insects are starting to answer the question of "What does it take?"—to have a personality, to learn, to teach others, to change the world around them—with the humbling and perplexing answer, "Not much." Humbling because they do these things with brains the size of a pinhead, and perplexing because if that's all it takes, what does that mean for us, with our gigantic forebrains and exhaustingly long periods of childhood dependency?

  Insects Are Essential

  If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.

  —E. O. WILSON

  WE ALSO keep coming back to insects because they are, however we may feel about them, extraordinarily important to the earth's functioning as well as our own. Insects help aerate the soil by burrowing through it, and nourish it by leaving their droppings. They eat dead plants and animals that otherwise would clutter up the planet, and release the nutrients back to the soil. They control populations of other invertebrates and vertebrates alike, by eating them or their food or by making them sick. In turn, insects provide food for other organisms. Perhaps most critical, insects are key pollinators of commercial and wild plants alike. All of these activities are performed to some extent by animals other than insects, of course, but the sheer magnitude of insect numbers means that they could not be eliminated without leaving a hole so large that, as Wilson says, the rest of the world's organisms would be unable to continue their lives.

  To make the worth of these ecological services, as they are called by scientists, more concrete, in 2006 John Losey from Cornell University and Mace Vaughan of the Xerces Society for Invertebrate Conservation calculated the economic value of four crucial tasks performed by insects: pollination, recreation, dung burial, and pest control of animals that eat crops, including other insects. They chose these categories because of the availability of data, not because of their perceived "importance," and acknowledge that the amount is almost certainly a conservative estimate. The total bill? Over $57 billion in the United States alone, and that just includes so-called wild insects, not domesticated honeybees or silkworms or other species that are reared commercially by people.

  The recreational aspect of insects is not, as you might initially think, due to people wandering around the countryside collecting butterflies to be pinned under glass. Instead, Losey and Vaughan examined the importance of insects to hunting, fishing, and wildlife observation, including bird-watching. Fish need to eat insects, and we use insects to catch them. Game birds such as grouse and pheasants rely on insects as food, as do waterfowl such as geese and ducks. And without grubs, flies, and beetles, all those lovely harbingers of spring—the warblers and flycatchers, woodpeckers, and swifts—would perish.

  Dung removal is probably not a service to which people give much thought, but our own sewage issues aside, everyone produces waste, as the children's book notes rather more colloquially, and it has to go somewhere. If it weren't for insects, that waste would just linger on the surface of the soil or in the water, tying up nitrogen that could be enriching the soil, and providing a breeding gr
ound for disease-causing organisms. Cattle also tend to shun grass that has been sullied by dung. By burying manure underground, dung beetles come to the rescue in many parts of the world, including the United States. They were introduced into Australia, where they do not occur naturally, to help process the massive quantities of dung produced by the cattle brought to that continent in the late eighteenth century. A friend of mine in Perth, Western Australia, worked with the Dung Beetle Crusade, a campaign sponsored by the government to help deal with the problem, and would take buckets of the beetles around the country.

  Pollination deserves a special mention, both because of its importance and because the recent decline in honeybee colonies makes the topic particularly timely. More than 218,000 of the world's 250,000 flowering plants, including 80 percent of the world's species of food plants, rely on pollinators, mainly insects, for reproduction. Losey and Vaughan cite a 1976 publication estimating that 15 to 30 percent of our diet in the United States relies on food sources requiring animal pollinators. In a typical fast-food meal of a hamburger, fries, and a milkshake, most of the components required an insect somewhere along the way; although the wheat in the bun is wind-pollinated, the other plants, from the cucumber for the pickle to the feed eaten by the cow, are insect-pollinated. Nicola Gallai from the University of Montpellier in France and her colleagues estimated the world economic value of pollination to be $153 billion, pointing out that this is nearly 10 percent of the value of agricultural production used for human food in 2005. Even more graphically, researchers with the Forgotten Pollinators Campaign in Arizona calculated that one in every three bites of food is made possible by a pollinator. We tend to think primarily about honeybees when it comes to pollination, but hundreds of bee and other insect species help pollinate crops, including the blue orchard bee, the southeastern blueberry bee, and the squash bee. Bees are about much more than honey.

  Insects Are Hidden

  DESPITE all of the aforementioned virtues, it is undeniable that insects will never fall into the category of what biologists call "charismatic megafauna," the large showy animals such as elephants and eagles that attract the attention of the public and help make the case for conservationists. When whales are endangered, people want to pass legislation and protest in storm-tossed boats. When a butterfly is endangered, people chuckle, and that's if they are feeling sympathetic. In the part of southern California where I live, endangered species are political footballs. Multimillion dollar housing developments can hinge on endangered species occurring on the land where they are planned, and when the Delhi Sands flower-loving fly was put on the list, people were not exactly imagining their wingbeats pulsing over the dunes as stirring music played, the way they would if the species in question were an eagle. It wasn't just that the flies were, well, flies, and hence lumped with vermin, it was that they were invisible to virtually everyone. Why should we save something we'd never even seen?

  Yet this seemingly innocuous, easily overlooked quality of insects, belying the extraordinary activity going on under our noses, is exactly what draws those of us in the know to them. In 1991, the Society for the Study of Evolution held its annual meeting in Hilo, on the Big Island of Hawaii. I wanted to go for the usual reasons one goes to scientific get-togethers: people would give talks on their most recent work, I could meet up with old friends and colleagues, and I could recruit new graduate students or collaborators. Besides, I had never been to Hawaii, and I was also excited about seeing the sights, from volcanoes to birds that lived nowhere else.

  I therefore decided to go a bit early to the Big Island, and entertain myself for a week or so before the meeting started. I have been studying crickets and their parasites since graduate school, and so it seemed obvious, at least at the time, that the entertainment would involve doing something with crickets in Hawaii. A colleague who had done postdoctoral work at the University of Hawaii in Hilo mentioned that an introduced cricket species, Teleogryllus oceanicus, was abundant on the lawns and vacant lots around the campus, and so I decided to collect some of them and dissect them to look for parasites. I now wonder just why this seemed to be the inevitable, or at least the best, option as a recreational activity, but regardless, the week before the conference found me and my long-suffering husband standing on the lawn near the university library, wearing headlamps and watching for crickets in the dark.

  Crickets are usually rather secretive animals, with the males staying hidden in burrows or leaf litter while they produce their melodic songs. But here, we kept seeing males out walking around on the surface of the grass, brazen as could be, and what was more, they weren't calling. Since calling is the only way male crickets can attract a mate, and since attracting a mate is a cricket's—any insect's—raison d'être, I was puzzled. What were the silent males doing?

  In what has turned out to be the only time in my life that I have impressed my husband, also a biologist, with my scientific acumen, I said to him, "The only place I can remember hearing about crickets doing this is in Texas, where they get these acoustically orienting parasitic flies. But I've never heard of any crickets here getting them. I suppose I should look."

  As you can probably guess, the next day I was dissecting the previous night's catch of crickets when a white maggot popped out of the body cavity of one of them, like a ghoulish jack-in-the-box. A little more work established that indeed, the crickets in Hilo—and, as it turned out, on Kauai and Oahu as well—didn't only attract the attention of amorous females when they called. They also risked being discovered by flies that use the chirps in a much more sinister way. Once a female fly locates a calling cricket, she deposits tiny larvae on him. A larva, usually one but sometimes two or even three, burrows inside the cricket's body and starts, ever so slowly, to eat his flesh while he is still alive. First it feeds on his body fat, but eventually, as the fly maggot grows until it occupies the entire body, from head to abdomen, it consumes the male's other organs, so that he is a shell that looks like a cricket but is pulsing inside with fly.

  I am interested in this grisly process for many reasons, but mainly because it exquisitely illustrates an evolutionary conflict for the males: it is terribly dangerous to call, because males risk attracting the attention of the flies, but calling is the only way to attract a mate. That week in Hilo got me started on a research program I have continued ever since, trying to discover how evolution has worked out the crickets' dilemma. We work, of course, at night, when most of the locals as well as the tourists are elsewhere, in places that tourists would never think to go, and watch as the drama unfolds in the grass. I have learned a great deal from the crickets, and the whole time I feel as if I am in possession of an enormous secret that no one else in the islands, as they drink mai tais and lie on the beach, has any idea exists.

  I am fully aware that from most people's perspectives, that's exactly as it should be, and that knowing about pale sticky maggots bursting Alien-like out of the living bodies of other organisms wouldn't enhance their Hawaiian experience one bit. But for some of us, that sense of being in on a hidden world is exactly why we remain fascinated by insects. Several years into the project, I brought my graduate student Robin to Hawaii to study the crickets, and on her first trip we set out a trap to catch some of the flies, a relatively easy matter because of their single-minded attentiveness to the sound of a cricket. All we had to do was play cricket song through a speaker with a tile placed in front of it; the tile was covered with a sticky substance so the flies couldn't get away once they had been attracted to the song.

  We turned on the recording and sat on a bench several yards away. After about twenty minutes I told Robin to go check the tile. She came sprinting back, visibly excited. More than a dozen flies speckled the tile, their wings buzzing in frustration. But Robin wasn't just satisfied at a successful experiment; she was also taken aback. The flies are not insubstantial, being about the size of a small housefly. But she'd never seen one before. Where, she wanted to know, had they been all this time?


  It's simple, I responded. You've never seen them because you don't have anything that they want. But now you know they are there, and what they are doing. And things will never be the same.

  It is exactly this feeling of a mysterious intricate drama being played out under our noses while most people remain unaware of its existence that makes us keep wanting to understand the lives of insects. Their stories seem unbelievable, with each life cycle, each mating ritual, more extraordinary than the last, and yet they are true. The rest of this book goes to places most people never see, as scientists uncover their secrets with techniques as new as proteomics and as old as a nose buried in the grass watching the bugs go by. We are changing our minds about what it takes to learn, about the nature of individuality, and about what a gene really does, all because of insects and the way they both reveal and reflect our own lives.