Head lice reproduce sexually, which is the case with most insect species. Adult male and female head lice of the species Pediculus humanus capitis are sexually dimorphic, with females somewhat larger than the males, according to the Centers for Disease Control and Prevention.
Head lice begin life by hatching out of eggs, called nits, that are cemented to the base of a single hair. After hatching, the nymph molts three times during the first seven days before reaching adulthood, according to the CDC. Fully grown head lice are typical insects in that they have six legs and a body that is divided into three sections. Each leg has a specialized claw foot for tightly gripping shafts of hair.
As an adult, the louse seeks out a partner and mates. A mated female louse lays as many as eight nits a day. Each nit takes between six and nine days to hatch, and it lives for up to 30 days without ever leaving the host's head, according to the CDC. During the reproductive phase of its life, an adult head louse must drink blood several times a day or face starvation, which usually kills the parasite within 48 hours of separation from its host.