Human infestation with lice. There are two biological varieties of the human louse, Pediculus humanus, var. capitis and var.corporis, each showing a strong preference for a specific location on the human body. Pediculus humanus capitis colonizes the head and P. h. corporis lives in the body-trunk region.

These lice are wingless insects which are ectoparasites. Their mouthparts are modified for piercing skin and sucking blood. The terminal segments of their legs are modified into clawlike structures which are utilized to grasp hairs and clothing fibers.

Lice are important vectors of human diseases. Their habit of sucking blood and their ability to crawl rapidly from one human to another transmit such diseases as typhus (rickettsial) and epidemic relapsing fever (spirochetal). The body fluids and feces of infected lice transmit these diseases.