The Monark Butterfly cycle from egg, to caterpillar, to an adult winged creature is truly amazing.

People of all ages are fascinated by watching the aging of the gangly caterpillar, and observing a green chrysalis (pupa state) transforming into a butterfly that quickly grows into an adult.  You may have seen experiments in school watching the Monarch progress through its stages.  The caterpillar feeds on milkweed to pupate, so placing a few caterpillars in glass jars with fresh milkweed leaves provides the perfect nursery to witness the transformation into butterflies.
  Under normal summer temperatures the egg turns into a caterpillar in about four to five days.  The monarch caterpillar searches for an appropriate spot to advance to its next stage.  It produces a small cocoon for itself and affixes it under a leaf or small branch.  Normally the entire process, from egg to butterfly, is completed in about two weeks.  During late spring to mid summer a pair of adult mating Monark Butterflies may only live from two to five weeks, but several generations will be produced.

However, as the longer and warmer days of summer evolve into the shorter and cooler days of late summer and early fall the Monarch’s evolution stages change.  Butterflies that emerge from the pupal state now are different.  The process from egg to adult stage will take longer, about a month now.  And this last generation of the summer season is identified to partake in the miraculous winter migration.  This generation is the longest lived, about eight to nine months, and able to survive the arduous migration to parts of Florida, the coastal regions of Texas, Mexico, and California, and retain enough strength for the return trip in the spring.

The Monarch Butterflies return to their same homes in the spring.  The breeding process resumes during this trip.  Following the rebirth of their food source, the milkweed plant, the youngest Monarch generation continues northward.  Many insect species can only mate once in their lifetimes, but Monarchs can mate several times in their short lifespan, deposit their eggs on milkweed plants, die, and be replaced with another generation.