Hind wings help butterflies evade predators

January 9th, 2009 - 2:04 pm ICT by IANS  

Washington, Jan 9 (IANS) Hind wings help butterflies and moths evade predators by taking swift turns.”To escape a predator, you don’t have to be fast, you just have to be more erratic,” said Tom Eisner, who co-authored a new study on the subject. He is an authority on animal behaviour and ecology and professor emeritus at Cornell University.

The study, recently published in the Proceedings of the National Academy of Sciences, has linked this ability of butterflies with bright hues as an added protection. In evolutionary terms, gaudy colours tell predators like birds to keep off them as they taste bad or chasing them isn’t worth the energy.

Anyone who has tried to net a colourful butterfly knows they are hard to catch, but this is the first study to show that a butterfly’s hind wings help them in evasive flight patterns.

Eisner and co-author Benjamin Jantzen, doctoral student at Carnegie Mellon University, clipped off the hind wings of butterflies and then filmed their flight using two cameras to get 3-D views of their flight trajectories.

They then analysed and plotted on a computer the insects’ flight velocity, acceleration, how fast they changed direction, the curvature of their path and more.

They found that clipping the back wings did not affect basic flight, but “we were able to show that removing the hind wings cut their turning acceleration in half”, said Jantzen. The butterfly’s hind wings scoop air and provide extra force to quickly turn when chased.

Eisner added that some butterflies have other qualities that are linked with their bright colouring as a sign for predators not to eat them. Monarchs also taste bad, for example, said a Cornell release.

Other studies have shown that distasteful butterflies are slower and easier to catch. Butterfly wings are also scaly, slipping easily from a bird’s bill, and if the butterfly is caught it’s found to be “mostly wrapper and very little candy”, said Eisner.

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