Flood Relief

Natural History, April, 2001 by Richard Milner

Ants that nest in underground colonies have developed various strategies to cope with flooding, including the formation of living rafts and the sealing of nest entrances. To deal with rain, arboreal ants often build their nests of waterproof leaves. But ants that nest in plant cavities, such as some of the eighty ant species that nest in and on Southeast Asian giant bamboos, have developed a unique strategy to bait out their colonies during heavy downpours.

Entomologists Ulrich Maschwitz and Joachim Moog, of Germany's Goethe-Universitat, studied the reactions of the bamboo-nesting ant Cataulacus muticus to the flooding of its nest, both in a Malaysian rainforest and in the Laboratory. These ants make their homes only inside the hollow segments of giant bamboo, where their colonies contain a queen, her brood, and as many as 2,000 workers.

When a nest became flooded, either by rain or artificially in the Laboratory, the ants responded first by trying to keep the water out. Two or three workers blocked the nest entrances with their broad, flat heads. If that tactic proved ineffective, however, scores of workers came forward and drank as much water as they could. Each one then left the nest with a full abdomen and excreted water droplets on the outer surface of the bamboo's stem. According to the researchers, "This cooperative `peeing' behavior is a new survival mechanism adaptive to the ants' nesting ecology." Experiments with two species of Cataulacus that do not live in hollow bamboo revealed no forms of water-bailing behavior. ("Communal Peeing: A New Mode of Flood Control in Ants," Naturwissenschaften 87, 2000)