Antsy home buyers

Natural History, July-August, 2002 by Stephan Reebs

In many parts of the world, ants set up house in hollow (or excavatable) swellings that form on tree twigs or leaves. The trees and ants live in partnership: the ants attack and feed on insects that eat the trees' leaves, and in return, the trees provide a home for the ants. In the tradition of "If you build it, they will come," ant trees typically grow these little chambers, or domatia (from the Latin domus, for house), without any prompting from the ants. But there is now evidence that the ants themselves can trigger domatia-like growths in some trees. Working from a crane some eighty feet up in the canopy of a rainforest in southern Venezuela, Nico Bluthgen, of the University of Bonn, and Jens Wesenberg, of the University of Leipzig, saw workers of the ant genus Pseudomyrmex biting holes in twigs of several Vochysia vismiaefolia trees already covered in domatia. Two weeks later, the twigs started to swell, and over the next two to three months, they doubled in diameter. Curious, the biologists also pierced holes in twigs (with a battery-powered drill) and found that this, too, led to swelling--which meant that the wounds themselves, and not chemicals released by the biting ants, were the triggers. (Many plants are known to swell in response to wounds.) The enlarged twig sections, both ant- and human-caused, were not hollow, but after observing ants carrying plant pith out of some of the holes, the researchers speculated that ants may excavate the swellings. If future work confirms their idea, it will be the first example of ants exploiting the swelling response in plants so as to increase their real-estate holdings. ("Ants Induce Domatia in a Rain Forest Tree [Vochysia vismiaefolia]," Biotropica 33:4, 2001)

Stephan Reebs is a professor of biology at the Universite de Moncton in New Brunswick, Canada, and the author of Fish Behavior in the Aquarium and in the Wild (Cornell University Press).