Butterfly 'stare' doesn't intimidate birds

08 March 2008

NO ONE likes being stared at. It has long been assumed that the eyespots of butterflies and moths tap into just that fear, but the true function of such wing patterns might be much simpler.

Martin Stevens at the University of Cambridge and colleagues made fake butterflies with a range of patterns on their wings. Some were round and "eye-like", others had square or barred patterns. They placed the fake insects in woodland, then recorded any bird attacks on them. The team thought that if eyespots function as a deterrent because they look like eyes then the butterflies with eye-like shapes should be attacked less. In fact, butterflies with eyespots survived no better than those with other obvious shapes. However, butterflies with the largest markings, regardless of shape, suffered 30 per cent fewer attacks (Behavioral Ecology, DOI: 10.1093/beheco/arm162). Conspicuousness, the team conclude, not eye mimicry, is what deters predators.

"Predators tend to stay away from highly conspicuous prey, possibly because most conspicuous objects in nature are toxic," says Stevens. "We think this is the primary eyespot effect." Eyespots in other animals probably did evolve to mimic eyes, the team notes. Hawkmoth caterpillars use eyespots to mimic snakes, for example.

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