An order of small wingless insects, permanently parasitic on mammals and birds. The Phthiraptera are one of approximately 30 major groups of insects and can be divided into four suborders, three of which (the Amblycera, Ischnocera, and Rhynchophthirina) are known as chewing or biting lice, and the fourth (the Anoplura) as sucking lice. Amblycera and Ischnocera are found on both mammals and birds, whereas species of Rhynchophthirina and Anoplura are confined to mammals. In total there are approximately 5000 known species, of which just under 70% are recorded from a single host species.