Black Swallowtail (Papilio polyxenes asterius)

Butterflies have four distinct stages in their life cycle :
egg, caterpillar, chrysalis and the butterfly.
The eggs usually are laid singly on the larval host plant.
The caterpillars that hatch from the egg feed on the host plant.
When full grown, the caterpillar sheds its skin and transforms
into a pupa. This is called chrysalis in the case of butterfly.
After 10 to 20 days, the butterfly emerges from the pupal case.