The concentric circles and eyespots on the wings of butterflies and moths, such as those found in this silk moth, not only look like real eyes, but can also appear to stare directly at the predator from multiple directions. Called the “Mona Lisa Effect,” this optical illusion can scare off an attacker and buy the insect enough time to escape.
Scientists suspect that the eye spot, which has a dark “pupil” in the center surrounded by a bright “iris,” looks like a real eye to predators. Hannah Rowland, an ecologist at the Max Planck Institute for Chemical Ecology in Jena, Germany, wanted to see if this false gaze direction contributed to the effect. has recently Frontiers of ecology and evolution.
First, Rowland and co-authors trained chicks to attack mealworms hiding behind two eye-spots on paper at the end of a runway. When the eye-spot pupil was directed specifically toward the chick, the bird would run and retreat toward the paper repeatedly, waiting several minutes before attacking. But when the students appeared to look away from the approaching chicks, the birds attacked within seconds. The centrally located pupil was not as effective as the pupil looking directly at the chick, but had a longer delay than the pupil facing the opposite direction.
“This suggests that they’re really paying attention to the direction of the eyespot pupils and perceiving them as eye-like stimuli,” Rowland says. He added that the most frequent concentric eyespots in the world may appear to chicks as a pair of eyes that follow them, regardless of approach angle.
Antonia Monteiro, an evolutionary biologist at the National University of Singapore, who was not involved in the study, says the study is a “cool” demonstration of eyepoint evolution.
“These butterflies can be encountered from all angles, so centering the pupil ends up being a pretty good thing,” says Monteiro. Still, the eyespots used in the study were a few millimeters larger than the largest commonly found in nature, she says, and chicks may have been even more frightened by the size of their paper eyes. .
