Living World / Unusual Organisms

Tschinkel believes that an ant colony grows just as a single organism does, by rules that guide interactions among its cells and between it and its environment, a process called embryogenesis. A colony is “produced from the single, mated queen through the rules and interactions of sociogenesis”—the process by which a society grows and changes according to its internal rules. “And just as mature organisms differ, reflecting the rules of embryogeny,” he says, mature ant colonies differ as well, reflecting variations in the rules of sociogenesis.

Tschinkel is trying to describe those rules. He studies, for example, how worker size, distribution, and labor patterns change as an ant colony grows, and how labor division by worker size and age helps shape the colony’s structure and habits. Such factors appear to organize the workforce the way a factory floor plan organizes personnel. Young workers start out low in the nest, looking after the brood and the queen, and then move upward as they age, taking on more-responsible jobs—“general nest maintenance, food preparation, seed storage. Finally, they move even higher to become guards and trash collectors and, at last, foragers.”

He is also documenting how new ant colonies begin, including some unusual variations on the model in which the queen digs a hole and starts things rolling. Although newly mated fire-ant queens usually found new colonies alone, sometimes they do it in cooperation with other newly mated queens that arrive on the scene simultaneously. That’s a puzzle because it would seem risky: Worker ants tend to kill all but one such queen. Sometimes a mated queen will settle in an orphaned, queenless colony, although she’s unrelated to the workers there, and take over as a kind of royal parasite. Tschinkel has no idea why the workers are willing to serve such a usurper. In addition, a new colony’s workers often steal a brood from other new colonies, whose workers steal it back, and so on, until one colony wins. Then all the workers go and live in the winning nest, thus abandoning a mother.

Ant-nest design has a basic theme, Tschinkel says: Vertical tunnels for movement and transport, and horizontal chambers for work, storage, and housing the brood. But nests differ in shape, number, size of chambers, and how they’re connected, depending on the species. With the Florida harvester-ant nest, for instance, the largest chambers are near the surface and closely spaced, becoming smaller and farther apart deeper in the ground. Small chambers are oval in shape; larger ones are multilobed and more complex.

But exactly how the workers “know” to generate these shapes is not so obvious. “As they’re doing the work, each worker responds to what needs to be done,” he says. “What are the properties of individual ant workers so that once each has made her contribution, the sum is a particular outcome?”