Certain wasps have a remarkable ability to recognize the faces of other wasps. And much like humans, these stinging insects are more attuned to those faces than they are to any other shape, including the caterpillars they eat, a new study has found.
The findings, which adds to the list of amazing abilities social insects have, offer insight into how animals become good at specialized tasks. The study also touches on a raging debate about how and why humans are so attuned to sets of eyes, noses and mouths.
The wasps are "phenomenally better at learning wasp faces than anything else we tested them on," said Michael Sheehan, a graduate student in evolutionary biology at the University of Michigan in Ann Arbor. "They're not just good at faces. Like people, the way they learn faces is different from the way they learn other images."
To a set of untrained and fearful human eyes, all wasps may look alike. But, if you're willing to get close enough to a variety of paper wasps called Polistes fuscatus, there are obvious differences in the colors and patterns that cover their faces.
Previous studies have shown that these wasps can both recognize faces and remember them for at least a week. Because this species lives in communities with multiple queens who must follow a strict hierarchy, the theory is that they developed facial recognition skills in order to more accurately know their place in line.
To find out just how good the wasps are at recognizing faces compared to other objects, Sheehan and colleague Elizabeth Tibbetts recruited a dozen wild female wasps to perform a simple T-shaped maze.
Individually, each wasp flew from the bottom of the T to the fork, where they could view an image on either side before picking one to touch. One of the two images delivered a mild and unpleasant shock. For each pair of images, wasps had 40 chances to learn which was a safer bet.
When wasps were shown two distinct wasp faces, it only took about 10 trials before they learned to consistently choose the right one, the researchers report Thursday in the journal Science. For the next 30 trials, they picked right about 75 to 80 percent of the time.
The insects were eventually able to perform as well when shown two different black shapes on a white background, but it took them a lot longer. It wasn’t until close to the end of 40 trials that they were scoring right with the same success rate. When asked to distinguish between caterpillars, the wasps were hopeless.
To look deeper into what it was about faces that mattered, the researches tested wasps on faces that were either lacking antennae or had scrambled parts so that, for example, eyes were on the wrong part of the head. In both cases, wasps struggled to distinguish between images.
A different species of paper wasp with a social structure that doesn’t favor face learning failed the face-recognition task completely.
All together, Sheehan said, the results suggest that facially oriented paper wasps learn faces in a way that is different from the way they learn other shapes.
Plenty of studies have shown an affinity for this kind of facial recognition in sheep, non-human primates and people, said Fred Dyer, a zoologist at Michigan State University in East Lansing. Researchers continue to debate what it all means.
One of the biggest lingering questions, Dyer said, is whether our brains have become equipped through evolution to specialize on faces in a unique way. Alternatively, it’s possible that we are born with a more general ability to distinguish between shapes and that we learn early on that faces are an important kind of shape.
It's a classic nature vs. nurture debate, and wasps could help provide some answers. By showing that such distantly related animals as people and wasps have developed similar skills, the researchers say their study suggests that the need to distinguish between faces has driven the evolution of both groups.
On the other hand, Dyer pointed out, there's still a possibility that the wild wasps used in the study had already built up expertise in faces from their life experiences, which could have boosted their performance. In studies of human aficionados, people who get a lot of practice looking at cars, postage stamps or even cheeses can distinguish between those objects as well as they can between faces. Those kinds of results imply that our sense of faces is learned instead of inborn.
"Faces are how we recognize each other and have social interactions and they are clearly important for our lives," Sheehan said. "Whether we learn faces or process them differently from other images is kind of an open question."