Sep 24, · Adult head lice are roughly 2–3 mm long. Head lice infest the head and neck and attach their eggs to the base of the hair shaft. Lice move by crawling; they cannot hop or fly. Head lice infestation, or pediculosis, is spread most commonly by close person-to-person contact. Head lice occur in people of all ages and races. Males are affected somewhat less than females. Children are most likely to become affected by a head lice infestation, and epidemics can occur in schools, day cares, and nurseries, but adults may become infected, most often through contact with infected children.