Chewing lice are small, dorsoventrally compressed insects and are parasites of virtually all birds (Fig. 1) and some mammals (Fig. 2). Many chewing lice are host specific, being found on only a single species of host. All chewing lice are permanent ectoparasites and complete their entire life cycle on the body of the host, where they feed mainly on feathers, dead skin, blood, or secretions. Chewing lice on mammals apparently do not ingest hair, rather they feed on skin and skin products (Waterhouse 1953). Some species of lice feed on the eggs and molting stages of mites and other lice, including members of their own species (Nelson and Murray 1971). Lice also ingest microbes, such as bacteria and fungi, which are of unknown nutritive value.
Johnson, K. P. & Clayton, D. H. (2003). Biology, ecology, and evolution of chewing lice, in Roger D. Price, Ronald A. Hellenthal, Ricardo L. Palma, (eds). The chewing lice: world checklist and biological overview, 24, 451-75.