Four days later the eggs hatch into caterpillars, which continue to occupy the same trees, eating the tender new leaves. In about 20 days, the caterpillar attaches itself to a branch and molts into a stiff chrysalis. The larva is covered with a mottled tan, yellow, and white pattern and closely resembles a bird dropping. But if this camouflage doesn't suffice and predators probe the larva, a hydraulic device, called an osmeterium, emerges from a slit at the front of the thorax and releases a flow of repulsive, odoriferous fluid. The pupae remain dormant usually for one year, but sometimes for several years, before the adult butterfly emerges for its final, airborne stage of life.
Most adults live only a few days and the longest-lived last only three weeks.
Most of the butterfly's original habitat was lost to development early in the century. Spraying for mosquito control further decimated the population. By the 1970s it survived only in Key Biscayne National Park and on the northern part of Key Largo. This limited habitat was thought to be secure, then Hurricane Andrew hit Florida in August 1992, passing right through the butterfly's population center. All of the butterflies, which were in their pupal state, were submerged beneath several feet of salt water for hours.