The flea life cycle encompasses four stages: egg, larva, pupa and adult. In appropriate conditions, a flea completes its life cycle in 18 days, but this time varies depending on the environment.
A female flea is capable of depositing 50 eggs per day on a host animal. The eggs quickly fall into the substrate, where they hatch in two days to several weeks. Flea larvae are approximately 1/4 inch in length, worm-like and translucent. They feed on the blood-rich fecal material of adult fleas for one or two weeks and molt several times before pupating. Flea pupae are silk cocoons capable of lying dormant for over a year until conditions are right for the adult to emerge; however, in an ideal environment, such as a warm home with the frequent movement of pets, adults emerge in three to five days.
The vibrations and carbon dioxide output of a passing animal triggers the final emergence of the adult flea. Adult fleas are flat on the sides and possess three pairs of legs. They are excellent jumpers that move easily from the ground to a passing host. Fleas need at least one blood meal before mating. While most fleas are adapted to feed from a specific host, such as a dog or cat, they can also bite humans when necessary.