The big black and gold symmetrical spots on butterfly wings deter predators because they resemble eyes in the darkness, right? Not necessarily. Here's an experiment that indicates that we see eyes, but animals don't.

We all learned that the big black spots on the wings of butterflies are "eyespots." They seem to turn the small, fragile butterfly into a fearsome and much larger predator. But how do we know that? One paper examines the evidence that animals are scared off by butterfly eyes.

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The authors take a look at past experiments, and find good evidence that animals avoid looking at "eye-like" structures. When baby chicks were exposed to a large stuffed hawk, they avoided it more when its eyes were uncovered. When the chicks were exposed to shapes painted on a mask, they didn't respond to diamond eyes, square eyes, or a lack of eyes - but they avoided circular eyes. Lemurs avoided looking at any shapes with two eye-like structures. Clearly some animals that eat bugs do look away when faced with things that resembled two eyes.

But a little more testing showed it wasn't that simple. Bright, alert-looking eye structures might work when they're on large animals, but when they're put on things that resemble small butterflies, they don't meet with the same success. A research group decked out fake butterflies with one, two, or three eyespots. They varied the eyespots between a dark pupil surrounded by a bright eye and a bright pupil surrounded by a dark eye. They changed the shape of the "eyespots." And suddenly butterfly-eaters like birds and small mammals stopped responding to the fake eyes.

While single eyes didn't intimidate birds, there was no difference in predation on fake butterflies with two or three eyespots. There was also no difference in predation between butterflies with round eyespots and rectangular eyesspots. There wasn't a difference between black pupils and light pupils. So while animals do tend to avoid eyes, there's evidence that they don't see eyes when they look at butterfly wings - they just see a profusion of colors and movement that they don't feel like messing with.

Top Image: Museum of Toulouse

[Sources: Current Zoology.]