Head lice spend their entire life on the host scalp and feed exclusively on blood, 4-5 times daily. Man is the only known host of this parasite. Although any part of the scalp may be colonized, lice favor the nape of the neck and the area behind the ears, where the eggs are usually laid.
During its lifespan of 4 weeks a female louse lays 50-150 eggs. From the egg hatches the first nymphal stage, which after three molts develop to nymph 2, nymph 3 and to either male or female louse. A new generation of lice can develop within a month (Fig. 3).
Female lice normally lay their eggs at the base of the hair, ca. 3 mm from the scalp, where the environmental conditions are favorable for the development of the embryo. Eggs are attached to the hair with quick-hardening glue, excreted from the body of the female. The young lice hatch 6 to 9 days later, leaving the eggshell (nit) behind.