Linked from
The 20 pages that link to Pupa, each with the reason it gives.
Complete metamorphosisBroader topic: Larval tissues are reorganized as adult structures develop.
CaterpillarBroader topic: After its final larval molt, a caterpillar enters the pupal stage.
CocoonBroader topic: The cocoon surrounds this developing stage in many, but not all, insects.
BirdwingBroader topic: Birdwing pupae reorganize larval tissues into adult butterflies.
Pieris brassicaeBroader topic: Large white larvae pupate before emerging as winged adults.