A butterfly is an insect belonging to the superfamily Papilionoidea. They are known for their delicate and beautiful wings and for their life cycle beginning as a caterpillar (or larva). The transformation from caterpillar into butterfly is an example of metamorphosis. The purpose of the stage as a caterpillar is for growth - the multi-legged caterpillar may shed its skin four times.  Most caterpillars consume leaves and eat abundantly. The caterpillar stage may last two weeks. 
The next stage is for the caterpillar (which is known as a pupa in this stage) to enter a chrysalis for about ten days. (The chrysalis is not a cocoon; a cocoon is a protective casing made out of silk by certain types of larvae, such as the caterpillars of typical moths.) The chrysalis will become transparent about 24 hours before the pupa escapes and becomes a butterfly.  The butterfly will struggle to escape the chrysalis, but this process gives it strength. Within several hours, the butterfly will have the ability to fly.
The Monarch Butterfly is one of the most easily recognizable butterflies, with its distinctive orange and black appearance. The migration cycle of this butterfly is tracked by a program called Monarch Watch, headquartered at the University of Kansas. Volunteers track monarchs, put small informational tags on them, and let them free again.  Trackers further south will search for monarchs with tags, and learn about the migration history of that monarch.