Michael Sheehan

Friend or foe? Wasps can recognize individuals they've fought with previously.

Wasps Make Peace With Past Enemies

Whether you're a worker in an office or a wasp in a nest, it's important to know who's who. Humans have intricate memories that allow them to keep track of individuals, but scientists have long thought that social insects like wasps eschew recognition of specific individuals in favor of general social rules that apply to everyone. But a new study shows that in fact, this isn't true--wasps do remember each other, suggesting that some building blocks of complex social relationships might be more deeply rooted in the animal kingdom than we thought.

Paper wasps, Polistes fuscatus, live in comb nests with hundreds of their counterparts and sometimes several queens. Unlike honeybees and other social insects, any paper wasp can potentially become a queen. Because of this, queens battle each other for rank, and fights regularly break out in the nest. Of course, it does no good for either the loser or the victor to rehash the same battles over and over, so wasps would benefit from recognizing and remembering each other. In previous studies, Elizabeth Tibbetts, an evolutionary biologist at the University of Michigan, Ann Arbor, found that paper wasps are more aggressive toward unfamiliar wasps from outside their own nests (ScienceNOW, 12 July 2002). She also found that wasps appear to use facial patterns to distinguish among their nestmates. So Tibbetts teamed up with University of Michigan ecology and evolutionary biology graduate student Michael Sheehan to find out whether wasps would remember their former rivals and save themselves the trouble of fighting again.

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I know you. Wasps don't fight with past enemies.
Michael Sheehan

Tibbetts and Sheehan collected 50 unrelated wasp queens from parks across Ann Arbor. They then introduced each wasp to an unknown wasp from a distant nest and let them get acquainted for 24 hours. "If you put wasps in a box together, they'll eventually fight over something," says Sheehan. And fight they did. The queens vied for dominance by lunging, snapping, and batting at each other. After the daylong bout, the wasps were removed to separate cages and reunited 7 days later. This time, instead of fighting, they mostly kept to themselves (see video above). To make sure their overall aggression levels hadn't decreased, Tibbetts and Sheehan had lined up new play dates for the wasps on the days before and after the reunion. Fights broke out in both cases (see video below), the researchers report today in Current Biology. With a brain about the size of the period at the end of this sentence, it's impressive that wasps have such robust social memories, Sheehan says.

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Attack! When wasps don't recognize one another a fight ensues.
Michael Sheehan

The research is elegant in its simplicity, according to entomologist Martha Weiss of Georgetown University in Washington, D.C. "It quite clearly shows ... individual learning in social insects," she says. It will be interesting for future research to determine whether the wasps are taking into account visual cues, scents, or both, she adds. Either way, it's interesting that this kind of social complexity can exist in such small brains, says Joan Strassmann, a social evolution researcher at Rice University in Houston, Texas. Strassmann says the study provides an interesting opening for future research to identify the neural and genetic building blocks of social interaction.

Posted in Plants & Animals, Environment