There are four distinct stages in the life of a flea: the egg, the larva, the pupa (or more commonly called "cocoon"), and the adult.
EGG STAGE
Flea eggs are barely visible to the naked eye. They are laid on the host animal and either fall off or are scratched off into carpeting and other upholstery, where they will hatch over a period of one to ten days.
LARVAL STAGE
When eggs hatch, fleas enter the larval stage which lasts one to two weeks, depending on the environment. Larvae prefer a dark environment and frequently feed in pet bedding, but will burrow into carpeting, cracks in floors and upholstery.
COCOON STAGE
Larvae begin spinning whitish cocoons (properly called pupae) where the worm develops into an adult flea, metamorphosing from the cocoon in as little as one week or as many as six months.
ADULT FLEA
Upon entering the adult stage, a flea will immediately seek a host to feed from and will be able to reproduce. Thus, the flea life cycle begins anew. The female flea will lay 20 to 50 eggs per day and can continue doing this for over three months. Two out of three fleas are female, so there is a possibility for huge infestations, in a relatively short time.