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By Root 475 0

’s really most sincerely dead.” Their proficiency at butchering prey is essential to their livelihood, due to the fact that they heft burdens by slinging them under their bodies. Although this group transport technique is efficient in that it allows the transporting ants to easily pull together in a common direction, it means that all booty must be carved up until the pieces will fit between a worker’s legs. The legs of rubellus are long, but not long enough to handle large prey whole unless it’s skinny, such as earthworms and centipedes, which can be straddled by up to six ants—though in my experience, the workers beyond the first can be meddlesome assistants. As often as not, they climb partially or entirely atop the food, to gnaw at it rather than aid in its transport.

GENERALISTS AND SPECIALISTS

Our bedding prepared for the night, Caspar and I joined four rifle-bearing park guards dressed in green uniforms, berets, and canvas boots at a nearby concrete outpost for a dinner of spiced boiled yams, plantains, and chicken. We talked to the men about the diet of Americans and Europeans, and then about the African army ants and what they eat—something that probably differs by species. Most, such as the congolensis-kohli complex species, go after just about any prey: we had seen them retrieve caterpillars and grubs and even watched them storming the flank of a relatively vast grasshopper, which suffered them quietly for a minute before exuding a noxious snowy foam behind its head and leaping to safety. The swarm-raiding rubellus, which also feeds indiscriminately, is likewise a “generalist predator.” There are other army ants, however, that have been found carrying only earthworms and have been described as “earthworm specialists.”5

How can we tell if a species is a generalist or a specialist?6 After all, an individual’s diet depends on a cascade of contingencies. Once an ant finds prey, the choices she makes depend on her colony’s needs, the time and energy required to pursue the prey, the risk involved (whether it is likely to hurt her or to waste her time by escaping), and the nutrients and energy it contains.7 Many ants, for instance, give termite colonies a pass because termites are so well defended. Other species, such as Gashaka’s Pachycondyla, display behavioral and anatomical adaptations that specifically aid in catching termites, such as body armor and strategies for recruiting a regiment and disabling termite soldiers—though a cafeteria experiment, in which scientists provide the ants with a buffet, might show that they eat other things as well. In fact, some prey are so defenseless that almost any ant may consume them: a helpless caterpillar, for example, must be hard to pass up. Finally, familiarity with local sources of food can also be a factor for some ant workers, just as it is for the person who grew up in Chengdu, say, and craves Sichuan cuisine for the rest of her life.8

But whether a species is a specialist or generalist is determined not simply by what it will harvest and eat but also by its foraging behavior. A specialist not only has the skills to catch a specific food but has a search strategy that targets its food source. Consider, for example, the specialist Centromyrmex ants, which live and die inside a termite nest. The workers have to be blind, tough, and strong-limbed to invade termite galleries, where they are unlikely to contact anything to eat but termites.9 If, instead, Centromyrmex took their termites by foraging more widely, and if they readily transported such easy prey as caterpillars back to the nest, with their adaptations to capture termites they could be defined as “specialists” with a varied diet. We might liken them to early hominids, who made tools to hunt mastodon but, only occasionally having opportunities to use them, dined mostly on other things. In the end, whether a species is considered a food generalist or specialist depends on whether a researcher is interested in, among other things, its morphology, activities, habitat choice, ecological role, or everyday diet.

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