Within 7 to 14 days, unless food has been scarce, the third larval stage is completed, and the larva spins a tiny cocoon and pupates. Usually after a week the adult flea emerges and begins its search for blood. Fleas are known to remain in the pupal stage from five days to five weeks in the absence of hosts. Adults emerge from the pupal case when vibrations from pets or humans let them know a host is near. This is one reason why people returning to an unoccupied home may suddenly be attacked by an army of fleas.
Fleas usually live and breed most heavily where pets rest.
Persons coming near these resting places are also subject to attack. If fleas are established in a home, they will feed on man as well as on the pets. The usual places of attack are the ankles and lower portions of the legs. Contrary to belief, fleas cannot go through several generations without having a blood meal. The entire life cycle of a flea can require from two weeks to two years.