The eyes have it – or do they?

25 February 2008
Posted by Chris Smith.

For 150 years, zoology students have dutifully learned that circular markings on animals, such as the so-called eyespots found on a butterfly's or moth's wings, are there because they look like the eyes of that animal's predator.

It was thought that these "eyes" scare off anything hoping to have a quick snack. But now researchers at the University of Cambridge have made a discovery to overturn this idea.

Writing in the journal Behavioural Ecology, the researchers tested how wild birds reacted to moths made out of paper, painted with an assortment of different eyespots and pinned onto trees in woods near Cambridge. They tested spots of different shapes, sizes and number, and with different levels of similarity to the birds' eyes. Attached to each of the artificial moths was an edible mealworm as a temptation for woodland birds such as the blue tits, great tits, blackbirds, and house sparrows.

The scientists found that artificial moths with circular markings lasted no longer than those with other conspicuous marks such as bars or squares. In fact, the team discovered that the predators were most put off by large sized spots, a high number of spots, and if the spots were generally conspicuous.

The researchers conclude that, in the wild, eyespots work because they are highly conspicuous features, not because they mimic the eyes of the predators' own enemies.

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