Caterpillars evolved their weird chubby little ‘prolegs’ from ancient crustaceans

Scientists have finally figured out where caterpillars got their extra sets of legs from. Turns out, these chubby little limbs originate from their crustacean ancestors over 400 million years ago.

Insects have six legs, except when they don’t. Caterpillars — the larvae of butterflies and moths — have additional sets of limbs known as prolegs. So do the larvae and even adults of a handful of other insects. These prolegs pose an evolutionary mystery, and scientists have long grappled over how and why they got them.