Butterfly 'stare' doesn't intimidate birds - life - 08 March 2008

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Butterfly 'stare' doesn't intimidate birds
  08 March 2008
  Magazine issue 2646. Subscribe and get 4 free issues.

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.

Evolution - Learn more about the struggle to survive in our comprehensive special report.

  From issue 2646 of New Scientist magazine, page 16. Subscribe and get 4 free issues.
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