their exclusive food. The tube through which food is ingested and saliva excreted during feeding is formed in most mites by apposing the sheath that contains the chelicerae against the hypostome. However, the trombiculids are an exception. Some species of mites (Analgidae) have adapted to feeding on keratin and skin debris amongst the feathers of birds, and other species have adapted to feed directly on internal tissues such as air-sacs or lungs (Cytoditidae and Laminosioptidae). Psoroptic mites feed superficially at the stratum corneum; the photograph of a histological section of skin infested with Psoroptes ovis, and the photograph of the surface of a host's skin infested with P. ovis looking like white dots, show this type of feeding. Sarcoptic mites feed by burrowing within the living layers of the epidermis, mainly stratum spinosum. Demodectic mites feed in a position technically external to the skin, between the epidermis and the hair shaft in hair follicles. Dermanyssid and trombiculid mites feed whilst external to the skin by piercing the skin with, respectively, their chelicerae or a stylostome feeding tube. Mites at other sites feed by using their chelicerae to scrape either at the skin surface, or at base of feather, or to penetrate and scrape at internal tissue such as air-sac or lung. Families and species of mites causing diseases of livestock Psoroptidae Psoroptes ovis is an example of a surface-feeding mite. It commonly infests sheep, and cattle are infrequently infested. Other common psoroptic mites are in the genus Chorioptes. Species of Psoroptes and Chorioptes are very similar in appearance and infest the same species of livestock hosts. A diagnostic aid to differentiate these mites is the shape of the leg suckers. In Psoroptes, these are a small, shallow cup on a long stalk, whilst in Chorioptes, they are deeply cup-shaped with a short stalk. Psoroptic mites as adults are just large enough to see with the naked eye and can crawl readily using long legs. Chorioptes infestations are found on cattle and horses. Psoroptes cuniculi infests rabbits, mainly on their outer ears. Psorergatidae This family includes the species Psorergates bovis which infests cattle and Psorergates ovis which infests sheep. They are similar in appearance to species in the Psoroptidae and infest the skin in a similar way, feeding superficially. Sarcoptidae Skin disease caused by sarcoptic mites is variably called scabies, or in some countries mange. (The adjectives 'mangy' and 'scabby' are