The caterpillars appear, sometimes in large numbers, as soon as the vines start to grow in the spring. Only the fact that passionflowers are extremely fast-growing saves them from being completely defoliated by the insects. The butterflies seek out areas of the plant that have no other eggs laid on them (the eggs are bright yellow and look like small pimples) and deposit single eggs, often on one of the tendrils. The reason they do this is because the young larvae are cannibalistic. Some species of passionflower actually have a pair of tiny yellow bumps at the base of each leaf which resemble the eggs, possibly to discourage butterflies from laying on that particular leaf since they perceive it to be already occupied.

When the caterpillars are ready to pupate, they attach themselves upsidedown to a stem or other support (sometimes there are several hanging from the eaves of our house) and they begin their metamorphosis. After shedding a thin layer of their exoskeleton, their body begins to change drastically. It looks like it swells up and turns all blistery, then smooths out and hardens into the chrysalis. The chrysalis can move slightly at the abdomen end and shifts back and forth to stay out of the hot sun or avoid a touch.
The butterfly emerges from the chrysalis just like all other butterflies: big-bodied, tiny-winged and soft. In a matter of minutes, the wings expand, then finally harden, and the butterfly can fly away.

Last summer we had a new visitor to our yard: a zebra butterfly (Heliconius charitonius). This is a tropical heliconid and it spent quite a bit of time hovering around the passionflower vines. Zebra butterflies have the slowest flight of any butterfly I've seen; they look like they're just drifting along with no effort at all.