By Lice Clinics of America

Head lice come in three stages: egg (called a nit), nymph (immature lice) and adult. (See the head lice life cycle.)

A head louse (the single form of lice) is a human parasite that lives off a person’s blood. It likes to live close to its food source (it can’t survive more than 24-48 hours off its host), so it makes its home close to the scalp. It has six claws that allow it to crawl around from hair strand to hair strand.

A female adult louse will lay eggs (about 88 during her lifetime) within a quarter inch (~0.5 cm) of the scalp, attaching the eggs firmly to a hair shaft. Those eggs are called nits, and unless they are removed with a lice comb or are killed some other way, they will hatch into nymphs. Nymphs crawl down to the scalp and feed off the host. Nymphs then grow into adult lice.

View lice pictures and lice videos, or learn more about how you can get lice and how you can kill lice.