Sean O'Donnell, a UW assistant professor of psychology, also found that the behavior of the wasps, Polybia occidentalis, was not related to competition over reproduction or to body size. This suggests that biting and other interactions in this and similar species may be an important means of regulating the division of labor in insect colonies, he said.

O'Donnell's findings, published in the current issue of the journal Behavioral Ecology, were based on detailed observation of three wasp colonies in a dry tropical forest in Costa Rica. He captured nearly 800 female workers from the three colonies, color-coded them with dots of paint on their thorax and observed their interactions. O'Donnell focused on females because this species of wasp is basically a female society and males seem to do little work.

The range of biting behaviors observed varied, ranging from mild to highly aggressive. O'Donnell divided the behavior into three categories: very mild that could be likened to a light poke in the ribs among humans, slow chewing-like biting, and highly aggressive biting where the recipient is doing its best to escape.

"These are not different behaviors but a continuum of the same behavior, and the intensity of biting can transition to a more aggressive form," said O'Donnell.

In addition, he observed that some individuals were the victims of simultaneous or serial biting. As many as six wasps were observed biting another individual either simultaneously or sequentially. Biting interactions typically lasted less than 30 seconds, but a few were extended for as long as 10 minutes.

"Biting seems to have a cumulative effect on the behavior of these wasps," O'Donnell said. "As the number
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Contact: Joel Schwarz
joels@u.washington.edu
206-543-2580
University of Washington
27-Jun-2001