Letters to a Young Scientist (9 page)
The face of a dacetine ant,
Strumigenys cordovensis
. Collected by Stefan Cover in Cuzco Amazonico, Peru. Imaged by Christian Rabeling.
A M
ENTOR AND THE
S
TART OF A
C
AREER
A
S A CALLOW,
severely undereducated eighteen-year-old student at the University of Alabama, I began a correspondence with a Ph.D. student at Harvard University named William L. Brown. Although only seven years my senior, Bill was already a leading world authority on ants. At that time there were only about a dozen experts on ants worldwide and he was one of them, not counting those who specialized on the control of pest species.
The most inspiring thing about Bill Brown was his devotion bordering on fanaticism—to science, to entomology, to jazz, to good writing, and to ants, in that rising order. He was, as I wrote of him in a 1997 memorial tribute, a working-class guy with a first-rate mind. He visited bars, enjoyed beer, dressed poorly by the stiff standards of the Harvard of his day, and mocked pretense whenever he encountered it in the faculty. But he was a godsend to the boy he befriended.
“Wilson,” he wrote his teenage follower, “you’ve made a good start with your project of identifying all the species of ants found in Alabama. But it’s time to get serious about a more basic subject, where you can do original work in biology. If you’re going to study ants, get serious.”
Bill, when I first came to know him, was at that time absorbed in classifying a group of species called the dacetine ants, limited mostly to the tropics and parts of the warm temperate zone. These insects are easily distinguished by their bizarre anatomy. Their jaws are long and hooked at the end and lined with needlelike teeth. Their bodies are clothed in various combinations of curly or paddle-shaped hairs; and, in many of the species, a spongy mass of tissue encircles the waist.
“Wilson,” Bill went on, “there are a lot of species of dacetines in Alabama. I want you to collect as many colonies for our studies as you can, and while you’re at it, find out something about their behavior. Almost nothing has been done on that subject. We don’t even know what they eat.”
I liked the way Bill Brown addressed me as a colleague, albeit one in training, like a sergeant instructing a private. If we had been in the U.S. Marines, I suppose I would have followed him to hell and back—or something like that, assuming there are ants living somewhere in hell. In spite of my young age and lack of experience, he expected me to behave as a professional entomologist. He insisted that I just get out there and get the job done. There was no hint of “get in touch with your feelings” or “think about what you’d most like to do.”
So, pumped up with his confidence in me, I got out there and got the job done. I began by molding a series of plaster-of-Paris boxes with cavities the size of those that wild colonies occupy in nature. I added a larger adjacent cavity where the ants could hunt for prey. Into many such cavities I placed live mites, springtails, insect larvae, and a wide variety of other invertebrates I found around the nests of dacetines in natural habitats. I was later to label this the “cafeteria method.”
My efforts were rewarded quickly. The little ants, I discovered, prefer soft-bodied springtails (technically, entomobryoid collembolans). As I watched them stalk and capture these prey, the odd anatomy of the dacetine ants made perfect sense. Springtails are abundant around the world in soil and leaf litter, and in some localities they are among the dominant insects. But ordinary predators such as ants, spiders, and ground beetles find them very difficult to catch. Beneath the body of each is a long lever that can be sprung violently but most of the time is locked in place—in other words, constructed like a mousetrap. When the springtail is disturbed even slightly, it pulls an anatomical trigger and the lever is released. Slamming against the ground, the lever catapults the insect high into the air. The equivalent acrobatic feat in a human being would be a leap of twenty yards up and a football-field distance forward.
The high jump works well against most predators, but the dacetine ant is built to defeat it. Upon sensing a springtail close by with the sensory receptors in her antennae—she is mostly blind—the huntress throws her long mandibles open, in some species 180 degrees or more, and locks them in place with a pair of movable catches on the front of the head. The huntress then slowly stalks the prey, literally step by cautious step. In the presence of a springtail, she is one of the slowest ants in the world. Her antennae wave side to side, also slowly, fixed on the location of the prey, turning to the right when the odor grows faint on the left, and to the left when the odor grows faint on the right, keeping the ant on track. Two long sensitive hairs project from the stalker’s upper lip. When their tips touch the springtail, the catch is pulled down, releasing the powerful muscles that strain at the base. The mandibles slam shut, driving the needle-sharp teeth into the soft body of the springtail. Often the prey is able instantaneously to release its abdominal lever, throwing it and the ant spinning into the air. I’ve often thought that if dacetine ants and springtails were the size of lions and antelopes, they would be the joy of wildlife photographers.
From my and Bill Brown’s early studies, various of which we published singly or together, a first picture of dacetine biology emerged. First, physiologists came to realize that the closing of the mandibles is one of the fastest movements that exist in the animal kingdom. Also the spongelike collar around the dacetine’s waist was discovered by later researchers to be the source of a chemical that attracts springtails, drawing them closer to the mandibular snare.
In time we and other entomologists came to recognize the dacetines as among the most abundant and widely distributed of all ant groups. Although their tiny size makes them inconspicuous in the soil and litter, they are an important link of the food chains of the world’s habitats. And, incidentally, colonies of many species live in rotting stumps like the one I described earlier.
During the next decade, Bill Brown and I took the next logical step into evolutionary biology. Armed with growing information, we reconstructed the changes in dacetines across millions of years, as they spread around the world and their species multiplied. In what manner and under what conditions, we asked, have the different species grown or shrunk in anatomical size? How and why did some of them evolve to build their nests in the soil and others in fallen twigs on the ground, or in rotting logs and stumps? A few, we learned, are even specialized to live in the root masses of orchids and other epiphytes of the rain forest canopy.
The history of the dacetine ants came into focus as we continued our studies. It turned out to be an evolutionary epic comparable to that of all the kinds of antelopes, for example, or all of the rodents, or all of the birds of prey. You may think that ants like these, being so small, must also be unimportant and deserving of less attention. Quite the contrary. Their vast numbers and combined weight more than make up for their puny individual size. In the Amazon rain forest, one of the world’s strongholds of biological diversity and massed living tissue, ants alone weigh more than four times that of all the land-dwelling vertebrates—mammals, birds, reptiles, and amphibians—combined. In the Central and South American forests and grasslands alone, one taxonomic group of ants, the leafcutters, collect fragments of leaves and flowers on which they rear fungi for food, making them the leading consumers of vegetation. In the savannas and grasslands of Africa, mound-building termites also rear fungi and are the primary animal builders of the soil. Although insects, spiders, mites, centipedes, millipedes, scorpions, proturans, pillbugs, nematodes, annelid worms, and other such lilliputians are ordinarily overlooked, even by scientists, they are, nonetheless the “little things that run the world.” If we were to disappear, the rest of life would flourish as a result. If on the other hand the little invertebrates on the land were to disappear, almost everything else would die, including most of humanity.
Because as a boy I dreamed of exploring jungles in order to net butterflies and turn over stones to look for different kinds of ants, I followed by happenstance the advice I gave you earlier: go where the least action is occurring. Just by any small twist of fate, I might easily have joined the large population of young biologists working on mice, birds, and other large animals. Like most of them, I would have enjoyed a productive and happy career in research and teaching. Nothing wrong with that at all, but by following the less conventional path, and by having an inspiring mentor like Bill Brown, I had a far easier time of it. I discovered early the special opportunity to conduct scientific research in rotting stumps and other microcosms that make up the foundation of the living world, but which then and to this day remain so easily passed by.
Martialis heureka
, the most primitive known living ant. Modified from drawing by Barrett Klein, Biology Department, University of Wisconsin–La Crosse (www.pupating.org).
