Adventures Among Ants - Mark W. Moffett [3]
A scanning electron micrograph of the marauder ant Pheidologeton diversus depicting the normal behavior of a minor worker riding on the head of a major. There’s a 500-fold difference in body weight between these two workers.
One day I spent hours rummaging through hundreds of the naphthalene-scented cabinets searching for the least-understood specimens. From childhood, I have had an eye for all that is quirky in the natural world. In those cabinets, accordingly, I was drawn to the ants with oddball heads and mandibles, curious body shapes and hairs. I wondered what their bodies said about their lives and habits.
Continuing my search the next day, I came upon three drawers labeled Pheidologeton, a name I had never heard before. The glass tops of the drawers were dusty, and their contents were in disarray. The dried specimens, glued to small wedges of white cardboard that in turn were affixed with insect pins to foam trays, had obviously not been looked at for many years.
I was struck at once by the ants’ polymorphism—that is, how different they were from one another in size and physical appearance. As in most ant species, the queen was distinctive, a heavy-bodied individual up to an inch long. But it was the workers that gave me an adrenaline rush. While the workers of many species are uniform in appearance, in Pheidologeton the smallest workers, or minors, were slender with smooth, rounded heads and wide eyes. The intermediate-sized workers, or medias, had larger, mostly smooth heads, and the large workers, known as majors, were robust, with relatively small eyes and cheeks covered with thin parallel ridges. The wide, boxy heads of the majors were massive in relation to their bodies, housing enormous adductor muscles that powered formidable mandibles.
I had never seen anything like this. The minor, media, and major workers didn’t look like they belonged to the same species. The heads of the largest workers were ten times wider than those of the smallest. The biggest majors, which I came to call giants, weighed as much as five hundred minors. The energy and expense required to produce these giants—and to keep them fed and housed—must, I thought, be immense, which meant they must be of extraordinary value to their colonies. I left the collection that day certain I had found something special: few ants display anything close to the extreme polymorphism of Pheidologeton.
As a student I knew that the best-studied polymorphic ants were ones I’d seen on my first trip to Costa Rica—certain Atta, or leafcutter ants, and New World army ants such as Eciton burchellii. These ants have some of the most complex societies known for any animal, giving them an exceptional influence over their environment. Their social complexity is due in part to the division of labor made possible by their varied workers, which, with their differing physical characteristics and behavior, can serve different roles in their societies. Called castes, these classes of labor specialists focus variously on foraging, food processing or storage, child rearing, or defense, such as when large individuals serve as soldiers. Given its minor, media, and major castes, I suspected that Pheidologeton would be a treasure trove of social complexity.
From reading the books of Jane Goodall and other modern naturalists, I had developed the view that the best path to a career in biology was to find a little-known group of organisms and claim it, at least temporarily, as my own. I