Scanning electron micrograph of a human head louse (Pediculus humanus capitis), magnified 80x at 8" x 10". Female head lice cement their eggs to the hair. These eggs, called nits, hatch in a week or two. The adult female lays five to ten eggs every day. The saliva produced by these lice causes inflammation of the skin, and the claws and sucking also cause itching.