Sunday, August 1, 2010

The false head hypothesis

The gray hairstreak butterfly, Strymon melinus.

This butterfly often perches upside down. It has tiny tails on its hind wings; when the butterfly is perched it occasionally rubs those wings against each other causing the tails to move. The black spot in the orange area is called an eyespot.

Upside down orientation, eyespot, and moving tails create the illusion of a butterfly's head!

Take another look. If you were a bird intent on eating that butterfly you might take a bite of the false head and be left with a mouthful of tails, wondering what happened, as the butterfly flew off in a totally unexpected direction.

(But some scientists think that birds preferentially attack butterflies from behind and the purpose of the false head is to deflect attacks toward the real head where the butterfly can see them coming.)


There is more information about urban insects in my book, A Field Guide to Urban Wildlife of North America, which will be published by Stackpole Books in spring 2011. 

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