of mites, Demodex, has adapted to infesting the hair follicles of its hosts. These mites remain external to the true outer layer of the skin (the epidermis) which also lines the tube of the hair follicle. However, the mites appear to be deep within the skin in the sense of being below the general outer surface of the host. The mites fit in the narrow space between the hair and the tube of the follicle. They may also crawl out onto the general epidermal surface of their host. Transmission of these mites from host to host occurs during close contact when young animals are suckled. Demodex mites are morphologically adapted to this constricted habitat: microscopic, worm shaped, and with very short legs. The mites feed on cells of the epidermal lining of the hair follicle. Many species of mammals, including humans, are readily infested with these mites, but typically the density of infestation is very low. However, they are considered parasitic in people with weakened immune systems. Dermanyssidae Dermanyssid mites are much larger than most parasitic mites and are easily visible to the naked eye. They have long, powerful legs that they use to seek their hosts and their size and active crawling cause them to resemble larval ticks. Their lifecycle proceeds from egg to larva to nymph to adult, and all of the active stages are only temporarily parasitic. A single blood meal is completed within a few minutes, so they are found on their hosts only for a short time relative to their time off the host. These types of mites naturally live in the nests of their bird hosts. The species of economic importance to poultry-rearing have adapted to living within the fabric of poultry houses. Their mouthparts are adapted for sucking blood with a pair of long piercing chelicerae. Dermanyssus gallinae, the poultry red mite, is typical. A related genus is Ornithonyssus—O. bursa, the tropical fowl mite, and O. sylvarium, the northern fowl mite. Mites as a direct cause of parasitic disease Mites found on surface of skin or within the epidermis Psoroptic skin disease The clinical manifestation of infestation with psoroptic mites is usually called mange and sometimes scabies, but the skin disease of sheep caused by Psoroptes ovis is often known locally as sheep scab. This species may affect its hosts severely enough to reduce their gain in weight. Costs to farmers of controlling