These are the "chewing lice". They are parasites mainly on birds, but some species infect mammals. All species are parasitic. The chewing lice are often grouped with the "sucking lice" as the Phthiraptera.
Adults mate and the female deposits eggs on the host, cementing them onto hairs or feathers. A nymph hatches and feeds. There are usually a few nymphal stages before the final molt to the adult stage. They feed on blood or tissue.
Chewing lice usually have dorso-ventrally compressed bodies, 1-6 mm long. They are wingless. Mouthparts are adapted for chewing and have large mandibles.