In complete contrast to most fleas or ticks, lice spend their entire lives on the host and are highly host specific, many species even preferring specific sites on their host's body. They usually only leave their host to transfer to a new one. To allow them to survive as permanent ectoparasites, lice show a large number of adaptations which enable them to maintain a close contact with their host. They are small insects, about 0.5-8 mm in length, dorsoventrally flattened and possess stout legs and claws for clinging tightly to fur, hair and feathers. All lice are wingless, but this is a secondary adaptation to the parasitic lifestyle. They feed on epidermal tissue debris, parts of feathers, sebaceous secretions and blood. They usually vary in colour from pale beige to dark grey, but they may darken considerably on feeding.
The Phthiraptera is a small order with about 3500 described species, of which only about 20-30 are of major veterinary importance. The order is divided into four sub-orders: Anoplura, Amblycera, Ischnocera and Rhynchophthirina. However, the Rhynchophthirina is a very small sub-order, including just two African species, one of which is a parasite of elephants and the other a parasite of warthogs. In the veterinary literature, the Amblycera and Ischnocera are usually discussed together and described as the Mallophaga which, in older textbooks, is accorded status as a sub-order in its own right. Mallophaga literally means 'wool eating' and the Amblycera and Ischnocera are known as chewing lice. The Anoplura are described as sucking lice. The description 'biting lice', sometimes used to describe the Anoplura, is a misnomer, because all lice bite.
Wall, R. & Shearer, D. (2001) Veterinary Ectoparasites: Biology, Pathology and Control. 2nd Edition, Blackwells Science Ltd, Oxford.