by the dozen to cart centipedes, worms, and other creatures that, if viewed through ant eyes, would appear bigger than dinosaurs to us. A few dozen minor workers, each about 3 millimeters long, easily hefted the head of one of the doves the Dengodis had tried to induce me to eat after they found out Americans eat meat. Later, Raja and I saw a seething mass of workers rip up a live, 2-centimeter-long frog, pulling its twitching body taut to the ground and then flaying the meat. Raja and I studied the action with both horror and a newfound respect. That was the day I named them marauder ants.
Marauder ants subduing a frog in southern India.
Though Sullia was in no danger from the ant swarms, it was easy to believe Bingham’s report from Burma that droves of this species could overwhelm a village. Raja enthusiastically told me how the ants would sometimes pour into the family pantry and make off with supplies of rice and dried condiments.
At dinner we reported to Raja’s parents about the marauders’ feats of predation, which I described as astonishing, particularly because the workers have no stinger, the weapon with which many predatory ants—especially those species in which the workers carry on alone or in small groups—disable victims. Mr. and Mrs. Dengodi, who took everything I said with great seriousness, no matter how eccentric the subject, listened as I explained that the marauders’ success with gargantuan prey seemed to rely on a coordinated group attack in which workers, individually inept, pile on high and deep, biting and pulling in such numbers that the victim doesn’t have a chance.
I could attest personally to the effectiveness of that approach. While watching the frog, I’d made the mistake of standing in a throng of marauders. The sheer volume of the minor workers’ bites was enough to drive me away, with one major lacerating a fold of skin between my fingers.
This scale of operations brought to my mind the most infamous raiders of all: the army ants.3 As a teenager in America’s heartland, far from any jungles, I had devoured popular descriptions of army ant swarms killing everything in their path. The stories often relied on florid writing, most famously in an unforgettable story by Carl Stephenson, first published in a 1938 issue of Esquire, “Leiningen versus the Ants”: “Then all at once he saw, starkly clear and huge, and, right before his eyes, furred with ants, towering and swaying in its death agony, the pampas stag. In six minutes—gnawed to the bones. God, he couldn’t die like that!” Although this is hyperbole, army ants do have an appetite for flesh and a coordinated battle plan that depends on sheer force of numbers.
Like many army ants, marauders have no stingers. Rather than incapacitating prey with stings, they mob it. This gang-style predatory attack is just one element of both ants’ complex routine. How much deeper did the resemblance go? I knew that currently there are as many species of ant as there are of bird—perhaps 10,000 to 12,000—and that the marauder and the army ant are no more closely related than the hawk and the dove.
Convergence is the process by which living things independently evolve to become alike, as a result of like responses to similar conditions or challenges. The wings of bats, birds, and bugs are convergent because they are limbs that have been independently modified to function in flight; the jaws of humans and the mandibles of insects are convergent because both can be used to hold objects and chew food. If the marauder ant and army ants proved to be alike in how they hunt and capture prey, it would be a similarly marvelous example of evolutionary convergence. That day in Sullia as I watched the ants dispatch that unfortunate frog, I made a decision that would affect the first years of my budding professional life: I would study the kill strategy of the marauder ant. I would make that my quest.
FEEDING THE SUPERORGANISM
Standing in a Sullia field on a tepid afternoon, with Raja’s guitar providing an incongruous musical accompaniment to the massacre at my feet, I felt like a general observing his troops from a hilltop and trying to make sense of the skirmishes below. My brain was whirling: one moment, trying to picture what it’s like inside one of those tiny, chitinous heads; the next, envisioning all the ants at once, forming a kind of arm flung over the ground with fingers that were rummaging through the soil and low plants.
The nineteenth-century philosopher Herbert Spencer was the first to treat in detail the simultaneous existence of these two levels, individual and society, and in 1911 the ant expert William Morton Wheeler came up with the term superorganism to describe ant societies specifically. Both men saw an ant colony not merely as an individual entity, as one might think of a bank or a school, but more specifically as the exact equivalent of an organism.4 They could readily make this point because others had already described the human body as a society of cells.5 The superorganism concept took on real meaning for me as I watched marauder ants. Before coming to India I had read an essay by the physician and ant enthusiast Lewis Thomas, who took Wheeler’s writings to heart:
A solitary ant, afield, cannot be considered to have much of anything on his mind; indeed, with only a few neurons strung together by fibers, he can’t be imagined to have a mind at all, much less a thought. He is more like a ganglion on legs. Four ants together, or ten, encircling a dead moth on a path, begin to look more like an idea. They fumble and shove, gradually moving the food toward the Hill, but as though by blind chance. It is only when you watch the dense mass of thousands of ants, crowded together around the Hill, blackening the ground, that you begin to see the whole beast, and now you observe it thinking, planning, calculating.6
Like a more traditional organism, a superorganism is most successful when its activities are carried out with maximum productivity at the group level. Consider the cells of a human body, an assembly of trillions. Although these cells may be doing rather little as individuals, collectively they can yield results as intricate and choreographed as a dancer’s in a corps de ballet. I developed a feeling for a marauder colony as an organism. I watched as the ants worked together like the organs in a body to keep the ensemble healthy and stable, with their trails serving as a nervous system used by the whole to gather knowledge and calculate its choices. With mindless brilliance, this colony-being established itself, procured meals and grew fat on the excess, engineered its environment to suit its needs, and fought—and on occasion reproduced—with its neighbors. I imagined that, given enough time, I could watch each superorganism mature, spin off successors that bred true through the generations, and die.
How do the members of an ant superorganism supply food for the whole? Unlike the body of an ordinary organism, a colony can send off pieces of itself—the workers—to find a meal. Regardless of species, once an ant detects food, her searching behavior stops and is replaced by a series of very different harvesting activities: tracking, killing, dissecting, carrying, and defending. In the majority of species, an ant can mobilize others to assist her. This communication practice is known as recruitment and usually involves chemical signals called pheromones. Often, a wayfaring ant releases a scent from one of a battery of glands on her body, a mixture that serves to stimulate or guide her nestmates. The mobbing of marauders at prey reflects the speed and effectiveness of their recruitment.
I’d known about recruitment, without having a name for it, since I was a child. At family picnics, I would drop a crumb in front of a lone worker. Within minutes, a hundred ants would be pouring along a column to the bread. Had I been able to inspect the successful hunter who first found the crumb, I would have seen her glide the tip of her abdomen on the ground on her return to the nest, depositing a pheromone that diffused in the air—a common, though not universal, ant practice. When ants form a line or travel in a column, they are tracking such a plume with their sensitive antennae, which they sweep left and right before them, in many cases while running faster for their size than any baying foxhound.
Each ant adds pheromone to a trail offering a good payoff, so the scent builds over time. Then, when the food supply runs low and the ants begin returning unrewarded, the pheromone is no longer replenished and
