June 2001

From University of Washington

Biting may drive division of labor among social wasp workers

Popular wisdom reminds people not to bite the hand that feeds them. But now a University of Washington researcher has found a species of social wasp that bites its fellow workers, prompting them to leave the nest and forage for the colony.

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 of incidents and severity of biting increase, the likelihood of an individual leaving the nest to forage increases."

His observations show that an individual wasp's life cycle tends to follow a pattern. The individual begins inside the colony's nest and then progresses to the outside, where it engages in biting behavior that sends other wasps off the nest to forage. Finally, it becomes the target of biting and goes off to forage. However, some individuals seem to spend most of their lives as either biters or recipients.

"This does not seem to be related to ovary development or body size so this behavior does not seem to be connected to reproductive status," he said. "We don't know what drives biting behavior. There is a possibility that it might be genetic, or it could be chemical because we do know that social insects tend to react chemically to each other."

He plans further work to determine the root of biting behavior in P. occidentalis.

Scientists like O'Donnell study social insects looking for clues about how social behavior evolved and how it is maintained since there are elements that are shared among all social animals. Social aggression is one such characteristic that is almost universal among animal groups from insects to primates.

The research was funded by the National Science Foundation.

For more information, contact O'Donnell at (206) 543-2315 or (206) 543-5325 sodonnel@u.washington.edu











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