No Respect for Male Wasps

The battle between the sexes in human society may pale in comparison to the one raging among wasps, according to a study in tomorrow's issue of Nature. Female paper wasps, researchers found, stuff males headfirst into empty cells of the nest, apparently trying to keep them from poaching food meant for female larvae. After imprisoning a male, the female worker typically keeps him pent up for up to 6 minutes, by pushing on his defenseless abdomen and threatening to sting.

Philip Starks, a graduate student in neurobiology and behavior at Cornell University, and Emily Poe, a Cornell senior, first noticed the "male-stuffing" behavior on a videotape made in the fall, when males idly hang around the nest before leaving to stake out new mating territory. Starks and Poe eventually observed 66 examples of "male-stuffing," all of which occurred seconds after females returned from foraging--suggesting that they are probably trying to make sure the males don't wolf the food. Starks thinks that other scientists may have missed the "strikingly aggressive" behavior because they studied wasp nests mostly in the spring, before the males are born.

Although it's tempting to think the females engage in "male-stuffing" out of irritation at the males' panhandling ways, Starks says the explanation is most likely genetic. Female wasps share, on average, 75% of their genes with their sisters but only 25% with their brothers. Thus a female forager, returning to the nest with a freshly killed caterpillar, has more incentive to feed it to a larval sister than to a brother.

"It's a very important study," says Laurent Keller, an entomologist at the University of Lausanne in Switzerland. Keller suggests that female workers might be trying to tip the sex ratio of the nest in their favor. The practice doesn't kill the males, but by giving more food to the female larvae, it "may produce larger females who are more likely to survive the winter."

Posted in Biology, Brain & Behavior