The Facts of Lice - Life Cycle
Egg / Nit
Lice eggs are laid by the adult female at the base of the hair shaft nearest the scalp. Lice eggs are firmly attached to the hair shaft by a glue-like substance and are oval-shaped, very small (about the size of a knot in thread), and hard to see. Lice eggs often appear yellow or white. Living lice eggs can appear to be the same color as the hair they are on. After hatching, the empty eggshell is called a nit. Lice eggs and nits are often confused with dandruff or other debris. Lice eggs usually take 8–9 days to hatch. Lice eggs that are likely to hatch are usually located less than ¼ inch (5mm) from the base of the hair shaft.
A nymph is a young louse that has recently hatched from a lice egg. A nymph looks like an adult head louse, only smaller. Nymphs, like adult lice, must feed on human blood to survive. Nymphs mature into adult lice 9–12 days after hatching.
A fully-grown adult louse is about the size of a sesame seed, has six legs, and is tan to grayish-white in color. Adult head lice may appear to be the same color as the hair they live in. To survive, they must feed on human blood. Head lice live about 30 days on a person’s head, but will die within 1–2 days if they are removed from a food source, such as when they fall off the head. Adult female head lice are usually larger than males and can lay about 8–10 eggs each day.