Monarchs are ravenous for milkweed. California pipevine swallowtail caterpillars want lots of pipevine. Why are these very hungry caterpillars so hungry?

“Caterpillars have to store up incredible reserves of proteins,” said Carol Boggs, an ecologist at the University of South Carolina. “Nectar doesn’t have much protein. Most of the protein that goes to making eggs has to come from larval feeding.”

Caterpillars are the larval stage of a butterfly. Their complete transformation to pupa and then to butterfly is a strategy called holometaboly. Humans are in the minority among animals in that we don’t go through these very distinct, almost separate, lives. We start out as a smaller version of ourselves and grow bigger.

But from an evolutionary point of view, the way butterflies transform makes sense.

“You have a larva that is an eating machine,” said Boggs. “It’s very well-suited to that. Then you’re turning it into a reproduction machine, the butterfly.”

See these eating machines in action as they fuel up and transform in this episode of KQED’s Deep Look.

Next: Monarch Butterfly Metamorphosis in HD, Witness butterflies emerge at the CalAcademy, and what happens to a caterpillar inside its chrysalis?

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