"Evolving a Defense, Mimics Save Themselves":

The Canadian tiger swallowtail caterpillar is a plump green creature that spends all its time munching leaves. It ought to be an easy meal for a bird, yet many birds pass it by.

The caterpillar is protected by a remarkable defense, researchers have found: it tricks birds into thinking it's a snake.

The caterpillar grows concentric yellow and black rings that look like a giant pair of eyes. When the caterpillar senses a bird nearby, it quickly inflates the front part of its body, making it resemble a snake's head.

Astonishing as this deception may be, the tiger swallowtail is hardly unique. Many species have evolved ways to fool would-be predators. Some insects look like twigs, even mimicking the way that twigs sway in the breeze.

Harmless snakes scare off predators by mimicking the look of venomous ones. Some species of hoverflies have the yellow and black stripes of stinging wasps. They even pretend to sting their enemies despite having no stinger at all.

But mimicry has revealed a puzzle at its heart: Time and again, scientists find examples of overkill. Animals don't seem to receive an extra benefit from making their disguises more elaborate.


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