They do not parasitize other animals. The head louse is a subspecies of the body louse. Head lice are generally more common in the U.S. than body lice. The presence of lice on the body is called Pediculosis.
Head lice occur primarily around the ears and back of the head.
In heavy infestations, they may also infest other hairy areas. Each female louse lays from 50 to 100 eggs, glueing them individually on the hairs near the scalp. The eggs hatch within 5 to 10 days. The complete life cycle from egg to adult takes about 3 weeks. Slight infestations may occur under the best of sanitary conditions, especially with school children.