An order of secondarily wingless insects comprising the sucking lice: blood-sucking ectoparasites of mammals, with piercing and sucking mouthparts forming a snoutlike proboscis. They constitute an irritating pest to humans and domestic animals and can transmit diseases, including typhoid. The human louse (Pediculus humanus) exists in two forms, or ecotypes: the head louse (P. humanus capitis) and the body louse (P. humanus corporis).