The face is familiar. So is the stinger.

Despite having a brain less than a millionth the size of a human’s, queen paper wasps of the Polistes fuscatus species can recognize one another’s faces. Michael Sheehan and Elizabeth Tibbetts, both of the University of Michigan, think they know why.

They suspected the wasps developed the skill to keep their home in harmony. The species forms large nests with several queens, and maintaining order is crucial. “If the queens know their place, it . . . keeps the peace in the colony,” says Sheehan.

The nests of a related species, Polistes metricus, each contain a single queen, so Sheehan and Tibbetts reasoned that these queens would be bad with faces.

To test the idea, they released wasps of each species into a T-shaped maze with an electrified floor. On reaching the junction, a wasp could turn left or right. Along each route was one of two images of a wasp face: One of the faces always led to a safe zone that wasn’t electrified; the other led to more shocks.

To avoid a shock, therefore, wasps had to tell the faces apart. P. fuscatus queen wasps could do so after 40 trials, but P. metricus wasps never learned the skill.

The result shows that facial recognition in wasps emerged because of evolutionary pressures, say Sheehan and Tibbetts.

Wendy Zukerman, New Scientist