Letters to a Young Scientist (10 page)
T
RACKING 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 the 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?
The next day, elated as I supposed only an entomologist can be, I took a bus inland to a stop close to the edge of the nearby rain forest. I was accompanied by an assistant assigned to me by the Museum of Natural History in Colombo. His principal role was to assure local Jainists, whose religion forbids the killing of all animal life even down to the lowly ants, that I had been allowed a dispensation. Along a forest trail I soon found several more
Aneuretus
colonies. I studied them in the field, during intervals between occasional pounding downpours of rain. Several colonies I placed in artificial nests to study their communication, care of the young and mother queen, and other aspects of their social behavior. Back at Harvard, I worked with several colleagues to describe the aneuretine internal anatomy.
Almost thirty years later, as a Harvard professor, I directed an undergraduate student from Sri Lanka, Anula Jayasuriya, as she made further surveys of the aneuretines for her senior honors thesis. She found that the range of the species was shrinking, which was no surprise due to the relentless clearing of Sri Lanka’s lowland forest since the time of my visit. At this point I had
Aneuretus simoni
put on the list of endangered species compiled by the International Union for the Conservation of Nature, one of the few rare insect species well enough known even to be considered for this category.
During this period, the picture of the evolution of the small but world-dominant ants as a whole was coming into focus. More researchers were entering the study of fossil and living species. We were filling in the steps in evolution that led to surviving groups, while discovering previously unknown groups and the ancestral lines that linked them together.
For a while the largest gap of all remained, the ancestor of all the ants. There is no such thing as a living solitary ant. All living species, so far as we know, form colonies with a queen and her sterile (or almost sterile) daughters, who do all the work. Males are raised in the nest solely for the purpose of mating with virgin queens. They leave the nest to find mates, are not allowed to return, and soon die. King Solomon, who instructed, “Go to the ant, thou sluggard, consider her ways, and be wise,” was obviously not aware of all the facts of ant biology in his moral urging. Nonetheless, how did this bizarre but extremely successful social system come into existence? When I was a young scientist we had many fossils to study, some dating back to more than fifty million years before the present, but every species represented had worker castes. Of the origin of their social organization we knew nothing.
This grail we ant biologists sought was a link still missing—a primitive ant with colonies like those of the ancestral forms that lived more than fifty million years ago, and simple enough to provide clues to the origin of social behavior. The leading candidate of which we had knowledge at this time was the Australian dawn ant (
Nothomyrmecia macrops
). Unfortunately, like the living aneuretines of Sri Lanka, the species was known from only two specimens. These had been collected in 1931 in one of the most remote places in the world. The land was the relatively inaccessible sand-plain heath of Western Australia. In the 1950s this vast area, stretching from the small coastal town of Esperance in the west to the edge of the desertlike Nullarbor Plain in the east, and covering over ten thousand square miles in area, was entirely devoid of people. Two decades before my own visit, a party of adventurers had traveled on horseback through this heath from the transcontinental highway south to an abandoned homestead on the coast called the Thomas River Farm, thence about a hundred miles west to Esperance. The terrain they crossed is one of the biologically richest in the world. In the seemingly barren scrubland lived large numbers of plant species found nowhere else on Earth. The insects were mostly unknown to science.
With the group in 1931 was a young woman who had agreed to collect ants along the trail for John S. Clark, an entomologist at the Museum Victoria in Melbourne and the sole expert on ants in Australia at that time. The collector carried a jar of alcohol into which she dropped ants wherever she found them. When Clark examined the specimens he was startled to find two belonging to a previously unknown ant species, primitively wasplike in form. It appears to be closest in anatomy among all known living ants to what may have been the ancestor of all ants. Unfortunately, the collector kept no records during the trek of where particular ant species had been found. The Australian dawn ant might have been picked up anywhere along a hundred-mile line.
By the time I arrived in 1955 to study Australian ants, I was obsessed with the idea of rediscovering this enigmatic species. It was already a legend among naturalists. I wanted to know whether it was fully social, with well-organized colonies of queens and workers, or less so—perhaps just partway to the advanced condition of all other known ants. Biologists of the time otherwise had no idea of how advanced ant social life had originated, or why.
Still young at twenty-five and charged with energy and optimism, I invited two fellow enthusiasts to join me in the effort to rediscover
Nothomyrmecia macrops
. One was Vincent Serventy, a famous Australian naturalist and authority on the Western Australian environment. The other was Caryl Haskins, a longtime ant expert and at that time the newly appointed president of the Carnegie Institute of Washington. We rendezvoused in Esperance, loaded up on supplies, and headed east in an old army flatbed truck along a dirt track to the Thomas River Farm. The flat plain, clothed in flowering shrubs and herbaceous plants, was beautiful to behold and blessedly empty—we saw only one other vehicle during the entire trip. From this base we searched outward in all directions, night and day, for the better part of a week. Dingoes prowled around our camp at night, the summer sun dehydrated us, and our footsteps turned huge meat ant nests into boiling masses of angry red-and-brown, viciously biting defenders. Was I afraid? Never. I loved every minute of it.
We devoted one day of our search to a trip northward to Mount Ragged, a prominence on whose barren sandstone slopes the dawn ants might have been collected. The only water source, for the 1931 party and ourselves, was a moist spot on the roof of a shaded ledge, from which enough water dripped to fill one cup each hour. No dawn ants were located there either.
Our overall effort yielded many new species of ants, but not a single specimen of the dawn ant. Because of my high expectations, the failure was one of the greatest disappointments of my scientific life.
Our failed expedition was nevertheless widely publicized in the Australian press, and it stimulated further searches in the sand-plain heath by entomologists. There was a widespread feeling among the local scientific cognoscenti that if this special insect was to be rediscovered and studied, it should be by Australians and not by Americans, of whom more than enough had already visited the continent.
One such attempt was led by my former student Robert W. Taylor, who had completed his Ph.D. at Harvard and at the time was a curator of entomology at the national insect collections in Canberra, the capital of Australia. Bob was desperate to make the discovery, to seize this grail for himself and for the honor of Australian entomology. On the way west to dawn ant country, the group camped in a forest of mallee, a kind of shrubby eucalyptus. The night was chilly, and there seemed to be no good reason to search for any insects at all. But Taylor walked out anyway with flashlight in hand, just in case something might be active. A few minutes later he came running back, shouting, “I got the bloody bastard! I got the bloody bastard!” As his words hint, now famous among entomologists, the dawn ant had indeed been found—and if not by an Australian, at least by a New Zealander.