What does a caterpillar become?

Inside the pupa the caterpillar does not sprout wings and grow up. It substantially dissolves. Most of its tissues break down into a nutrient soup, and the adult is rebuilt from small clusters of cells called imaginal discs that were present, dormant, all along - one for each wing, each leg, each eye.

Something survives the demolition, which is the genuinely unsettling part. Experiments with tobacco hornworms trained caterpillars to avoid a smell paired with a mild electric shock, and the moths that emerged still avoided it. Memory persisted through the reorganisation of the brain that held it.

Butterfly or moth is a soft distinction. There is no clean scientific line between them - the usual rules of thumb, antennae with clubbed tips, wings held upright at rest, flying by day, all have plenty of exceptions. Moths outnumber butterflies by roughly ten to one, and butterflies are best understood as one branch that happened to take up daylight.