In a single colony of P. fuscatus, there are often multiple groups of wasps led by cooperating queens. By constantly battling each other, the queens set up a power structure in the colony, determining food distribution, work assignments and reproductive privileges. Each wasp has distinct markings on its face and abdomen. When Tibbetts painted yellow markings on a wasp, the insect suffered considerable aggression from former colony friends, though not as much as if it were an actual invader. The wasps knew by scent that the painted insect was a nest mate, but they couldn’t recognize the insect by appearance and were unsure if it posed a threat to rank. Eventually, the wasps were able to learn the facial markings and assign a rank. Researchers set up a T-shaped maze and electrified the entire floor except for one arm of the maze. They placed an image of a P. fuscatus face in an electrified wing, and a different P. fuscatus face in the safe wing, which changed locations with each trial. They trained 12 wasps to associate one of the faces with safety. They then repeated the experiment using different paired images, including simple black-and-white shapes, caterpillars (their food), antenna-less faces, rearranged P. fuscatus faces and faces of a closely related paper wasp, Polistes metricus. They found that the wasps were able to discriminate between the normal P. fuscatus faces much more rapidly and accurately than any of the other images, suggesting that the insects have evolved specialized face-learning abilities. Perhaps the wasps can distinguish other things, such as shapes or rearranged faces, but they don’t respond to these with changed behaviors. The researchers also performed the experiment with P. metricus wasps, which don’t form multiqueen colonies, and found that the species does not learn faces any better than other images.
First posted: THURSDAY, DECEMBER 1, 2011