Letters to a Young Scientist

by Edward O. Wilson

  In patches of moss and lichens that grow on the surface of the stump—little worlds of their own—roam the aforementioned tardigrades, also called bear-animalcules for their body shape midway between caterpillars and miniature bears. Among these animals are the most abundant of all: the nematodes, also called roundworms, most barely visible. Worldwide, roundworms are reckoned to make up four-fifths of all the individual animals.

  If my staccato listing confuses you, like a page torn from a telephone book, rest assured it also confuses most biologists as well, and yet it is only the beginning of a very long roster that could be called out from our stump.

  Throughout the decaying wood, fungal strands penetrate, the hyphae hanging in gossamer strands when the bark is pulled free. Microscopic fungi abound wherever there is moisture. Ciliates and other protistans swim in films and droplets of water.

  All of the life of the stump ecosystem is dwarfed, however, in both variety and numbers of organisms, by the bacteria. In a gram of detritus on the surface or soil beneath the stump’s base exist a billion bacteria. Together this multitude represents an estimated five thousand to six thousand species, virtually all unknown to science. Still smaller and likely even more diverse and abundant (we don’t know for sure) are the viruses. To give you a sense of relative size at this lowest end of the stump-world scale, think of one cell of a multicellular organism as the size of a small city. A bacterium would then be the size of a football field and a virus the size of a football.

  Yet—all of this ensemble, as we pause next to it for an hour or a day, is no more than a snapshot. Across a period of months and years, as the stump decays further, there is a gradual change of species, the numbers of organisms in each species, and the niches they fill. During the transition, new niches open and old ones close as the stump evolves from hard fresh-cut wood leaking resin to rotting splinters leaking nutrients into the soil. Finally, the stump becomes no more than crumbled fragments and mold, infiltrated by roots of invading neighbor plants and covered by dead twigs and leaf litter fallen from the canopy of the trees above. Throughout, the stump is a miniature ecosystem.

  At each stage of decomposition, the stump’s fauna and flora have been changing. In each cubic centimeter of its living and inert mass, the system has been passing energy and organic matter back and forth to the surrounding environment.

  What could you make of this special world, should you choose to become an ecologist or biodiversity scientist and study it? How would you and your fellow researchers encompass the nearly infinite variations in Earth’s biosphere represented by this microcosm? So much has been written, yet so very little is known—even the full census of stump-dwelling species and those of countless other kinds of miniature ecosystems on the land and in the sea remain unknown, unrecorded, unwritten. Drastically less has been learned of the lives and roles of each of the species in turn. Their combined order and process exceeds everything of which we have knowledge in the rest of the universe.

  Keep in mind that a distinguished career of scientific research can be built from any one of the species, by means of contributions to different disciplines within biology, chemistry, and even physics. Karl von Frisch, the great German entomologist who made many discoveries concerning the honeybee, including their symbolic waggle-dance communication and their remarkable memory of place, knew that he had only begun to explore the biology of this single insect species. “The honeybee is like a magic well,” he said. “The more you draw, the more there is to draw.”

  III

  A LIFE

  in

  SCIENCE

  The face of a dacetine ant, Strumigenys cordovensis. Collected by Stefan Cover in Cuzco Amazonico, Peru. Imaged by Christian Rabeling.

  Eleven

  A MENTOR AND THE START OF A CAREER

  AS 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 o
n 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).

  Twelve

  THE GRAILS OF FIELD BIOLOGY

  TRACKING THE HISTORY of the dacetine ants, Bill Brown and I came to focus on what appears to be the most primitive living species, similar to the ancestral species that long ago gave rise to the worldwide tribe of dacetines alive today. Our quarry was Daceton armigerum, a big insect as ants go, roughly the same size as the half-inch-long carpenter ants found everywhere in the north temperate zone. Covered with spines, its long jaws flat and armed at the tip by sharp spines, it was known to occur on trees in the rain forests of South America. Otherwise, entomologists had almost no information on where it nests, the social structure of its colonies, how and when it forages, and the kind of prey it hunts. It became, for a short while at least, my personal grail.

  Very early in my ant-hunting world travels, I arrived in Suriname, at that time known as Dutch Guiana. I went immediately into the rain forests around the capital city of Paramaribo to search for the big dacetine. After a week of sweat-soaked work and failure, I enlisted the help of resident entomologists. They in turn sent forth their assistants and a few other forest-savvy locals who had seen the ant and had a good idea where to look. Soon a colony was found. It was where I had not looked—in a small tree growing in a dense, seasonally flooded swamp. We cut the tree down and carried it in segments to a laboratory in Paramaribo. There I carefully and lovingly sliced open the trunk, revealing a cavity in which the entire colony lived—queen, workers, brood, and all. Studying it (and, later, a second colony I found in Trinidad), I filled in the blank spaces: The colonies are composed of several hundred workers; the foragers go out singly to search for prey in the canopy; each worker hunts on its own, catching insects of a wide variety, all of which are larger than springtails and other prey sought by smaller known dacetines. And more.

  It is common for biologists to make a scan of biodiversity in order to locate some especially promising species or other, like the primitive giant dacetine, that offers opportunities to make a discovery of unusual importance. Another expedition I launched with the same goal in mind was to Ceylon, now known as Sri Lanka. The aneuretine ants found there I knew to be as distinctive a group as the dacetine ants. Unlike dacetines, however, aneuretines are not among the dominant insects of the world at the present time. In fact, they are on the edge of extinction. Their high moment in the evolutionary sweepstakes came long ago, toward the end of the Mesozoic Era, the Age of Reptiles, and continued on for a while into the early Cenozoic Era, the Age of Mammals—in other words a hundred million to fifty million years ago. We knew from fossil remains that aneuretines were both diverse and relatively common during the latter period. But of their social organization, their nests, their colonies, their communication, their food habits, we knew nothing. When I was a young researcher at Harvard, I was aware that in the late 1800s two specimens of a living species, Aneuretus simoni, had been collected in the six-hundred-year-old Royal Botanical Gardens in Peradeniya near Kandy, in the center of Sri Lanka. But no other specimens of the small dark-yellow ant had found their way into collections since that time.

  Was the last living aneuretine species extinct? Had it gone the way of the dodo and Tasmanian wolf during such a brief interval of time, after tens of millions of years of life? I felt compelled to find out. Another grail! In 1955, at the age of twenty-five, I disembarked from an Italian passenger ship at Colombo and went straight to the Udawattakele, the forested pleasure garden of the kings at Kandy, which seemed to be the most promising semi-natural site. For a week I searched throughout the daylight hours. I came up with nothing, not even one stray aneuretine worker. I then proceeded to the more disturbed grounds of t
he Peradeniya gardens, the source of the original specimens. More close searching, still no Aneuretus. It seemed indeed possible that the species I sought, and with it the great evolutionary assemblage of the aneuretine ants, might really be gone.

  But this verdict was unacceptable to me. So I traveled south to Ratnapura, resolved to hunt for the ant out from the city and into the nearby rain forest, which at that time stretched almost continuously to Adam’s Peak.

  Upon arriving in Ratnapura, I checked into a rest house, washed up, and within the hour strolled over to a nearby reservoir, where, although the shore was torn up by pedestrians and grazing cattle, I had noticed a thin grove of trees. I idly picked up a hollow twig lying on the ground and snapped it in two, expecting nothing much of interest to be living inside. Instead, I was stunned when out poured a stream of angry Aneuretus. I stood there staring at this wonderful gift. I paid no attention to the irritating sensation of the workers pouring over my hands. Would an Audubon scholar, in comparison, be bothered by a paper cut upon discovering a new original folio?