Adult head lice are small (2.5–3 mm long), dorso-ventrally flattened and entirely wingless. The thoracic segments are fused, but otherwise distinct from the head and abdomen, the latter being composed of seven visible segments. Head lice are grey in general, but their precise color varies according to the environment in which they were raised. After feeding, consumed blood causes the louse body to take on a reddish color. The eggs of lice are called nits. They are oval white cylinders (1/16 inch long). The eggs of head lice are usually glued to hairs of the head near the scalp. The favorite areas for females to glue their eggs are near the ears and back of the head. The egg must feed within 24 hours or they will die.
Egg, nymph, adult
Human louse infestation, called pediculosis, can spread rapidly and may reach epidemic proportions if left unchecked. Head lice are highly dependent upon human body warmth and will die if separated from their host for 24 hours. Head lice prefer to live on the hair of the head although they have been known to wander to other parts of the body. Head lice do not normally live within rugs, carpet, or school buses.
When an infestation becomes known, it is advisable to examine all members of the family, especially other children, and others who have been in contact with the infested person within recent weeks to be sure that they have not become infested.