Adventures among Ants. Mark W. Moffett

in the Western Ghats of India, I saw this system used by Leptogenys. The tight pack of slim, glossy ants was moving through the dry litter at the reckless speed of an Indian bus driver. I followed and watched as they entered the mud galleries of a termite colony. The ants soon emerged, each with a stack of termites in her jaws. This regimented form of group predation was a joy to observe, as long as I stayed back far enough to avoid the needlelike stingers that Leptogenys use to immobilize their prey in one-on-one combat. Later I determined that this species employs scouts. These individuals then return by themselves to the nest and recruit a few dozen nestmates who together do the potentially dangerous work of mining and transporting the unwieldy termites.

      Army ants employ a completely different foraging technique. Rather than proceeding with guidance to food already found, the workers sweep ahead blindly in a mass, the absence of a single target turning the whole raiding business into a gamble.

      Some army ants regularly invade homes, and in the underdeveloped world their arrival is welcome (even though they force everyone out for an hour or two), for they clear out vermin such as roaches and mice. Marauder ants perform a similar service—though they also make a nuisance of themselves by absconding with grain and other human foods, as Captain Bingham recorded.

      Indeed, it was impressive to watch marauder ant mobs take on centipedes and frogs in India. From those clashes I saw that, like army ants, marauders recruit members explosively as each prey item is found, then kill and cart off the bodies together. But to understand marauder ant foraging behavior, I needed to learn how they located their prey in the first place.

      After a time, Raja tired of the ant bites and stayed home to practice his guitar. By then I had been in Sullia three weeks, surviving on sticky rice splashed with a red curry so spicy that it often left me panting. This diet kept me ravenous, and to sustain my energy I purchased caramels at a roadside stand. (The shop had more ambition than inventory, with the former evidenced by its name, Friendly Mega Supermarket Store, which was crudely painted on a board.) I surreptitiously devoured the candy at night, fearful of hurting my host family’s feelings, and disposed of the paper wrappers down rodent burrows on the plantation.

      One cool evening as I watched marauders rushing in the tree litter, as greedy for high-calorie food as I was, a vision of the ants as a superorganismic being crystallized in my mind. I began to think about the army ant stratagem of foraging in a “group.” Within the superorganism, what does membership in such a group entail for an ant? Is it proximity? Among humans, techniques as old as jungle drums and as new as Twitter allow people to form groups without physical closeness. Conversely, being close to others does not automatically confer membership in a group in a meaningful way. Often enough I have joined a crush of people on a city street—quite a crowd, but not much of a group.

      I had seen many ant species in which nearby workers show no semblance of joint action. Is proximity even less meaningful to ants than to people? In many ways, yes. The workers of most ant species cannot detect another ant’s presence until they are virtually on top of each other. Army ants, legally blind by human standards, sense a nestmate only during fleeting moments of contact. In such times, the ants distinguish friend from foe, but what they learn is unlikely to play a role in the organization of their armies. Rather than responding directly to others, ants tend to react to information left by nestmates who may be long gone—to the webwork of social signals, such as pheromones, spread throughout the environment in an ant version of the Internet.

      Think of household ants following an odor trail to a cookie left on a kitchen counter. What happens if I pluck out all but one ant? Her actions won’t change an iota as long as she can track the scent. She continues to participate in a group effort to harvest food whether the trail is thick with ants or not. Could we define an ant as being part of a group when her actions are constrained or guided by the varied signals and cues arising from the actions of her nestmates, and as solitary when she acts on her own?¹⁵

      As it turns out, army ants conform to this view of a group. The workers have negligible freedom to wander far from nestmates and any fresh chemical communiqués those nestmates have left behind; the superorganism never sends out lone pieces of itself, but droves of workers operate as an almost tangible appendage that stays attached, through a continuous flow of ants, to the main body. Some scientists point to other aspects of army ant life, such as their ability to catch or retrieve prey in groups, but it is this aspect of their behavior—how they forage, and not what they do after they find food—that sets army ants apart from other ants.

      My goal became to determine whether the marauder ant uses the army ant group approach to hunting. In India, I documented the movements of teeming battalions, with the workers numbering in the tens of thousands. But such details as whether the raids relied on scouts were difficult to assess during the bone-dry weather I experienced there, which forced the ants to be cryptic and subterranean. I would continue my marauder ant studies in Southeast Asia, where the species was common.

      Rajaram Dengodi, smiling dreamily as he strummed his guitar, saw me off on the bus to Bangalore. As I climbed the steps, the proprietor of the booth where I had been buying caramels ran over and gave my hand an enthusiastic shake. He had gone upscale, with fresh paint and a fancy poster of the Indian deity Ganesha. I wondered how much of my patronage had gone into subsidizing his new, neatly lettered, laminated sign: FRIENDLY MEGA SUPRMRKET STORE.

      HOW TO HUNT LIKE AN ARMY ANT

      A year later, in Irian Jaya, Indonesia, the dryness of southern India was long forgotten. The rain was so thick and the air so muggy in the Cyclops Mountains that I felt like I was walking in a bowl of hot soup. My kinky-haired guide, Asab, had to scream his customary question over the roar of water battering leaves: “Sudah cukup?” (“Had enough?”). In the heavy rain I could barely see the ancient Russian machine gun slung over his shoulder—protection, he had told me, from guerillas.

      For two days the downpour was nonstop. I slept in wet clothes. My camera, though sealed in a plastic bag, somehow got waterlogged. I was often up to my waist in mud, making it difficult, at best, to locate ants. The few specimens I did manage to collect were washed away in the middle of the night, along with the majority of my toiletries. Fortunately, my other experiences in most of Southeast Asia were far more pleasant and productive.

      I had embarked for Irian Jaya from Singapore, where I would be based for two years. In India, on my diet of rice and caramels, the weight of my six-foot frame had dropped to 138 pounds; since then I had gained back twenty pounds, largely from my time in Singapore. It was hard to resist a country so immaculate and orderly that bubble gum is illegal and so attuned to style that when the Straits Times announced that Paris fashions had shifted from red and white to black, all the girls were wearing black within the week. For anyone on a student budget, moreover, Singapore was a dream come true: roti parata, fried kway tiao, Hainanese chicken rice, Hokkien noodles, and ice kachang are just some of the foods from the hawker stalls near Orchard Road that I frequented. Of more academic consequence was the University of Singapore; I often found myself nursing Tiger beer with ruddy expat professors, feeling like a character in an Anthony Burgess novel.

      I rented a tiny room in a high-rise from a Chinese family whose composition kept changing. Each evening, I would return from ant-watching to find their apartment in darkness and would tiptoe past a dozen or more people sleeping in rolled blankets on the floor. At sunrise, I would be awakened by soft Cantonese voices and an aroma of tea. We had no idea what to make of each other, they with their elegant apartment managed like an ant heap, and me, the muddiest human in Singapore, leaving a trail of ants wherever I walked.

      Sir Thomas Stamford Raffles, the early-nineteenth-century British colonial agent who founded Singapore, was a keen naturalist. His love of nature is manifest today in a Singaporean fondness for parks and gardens. This meant that there were plenty of places to observe marauders, since they do well in deteriorated natural habitats and on human-altered terrain. Lawns and gardens and the weeds that colonize human clearings almost always contain abundant supplies of high-energy food. Plants in open spaces allocate more resources to rapid growth and dispersal and less to defenses against herbivores or competitors. That means they can support more plant feeders, and thus more of the predators that eat them, including insatiable