Mite, common name for some 30,000 species of minute, usually oval-bodied arachnids. They are worldwide in distribution. Mites resemble ticks in having the head, thorax, and abdomen fused into one unsegmented body, but they are usually much smaller. They often have three pairs of legs in the larval stage and four pairs of legs in the nymph and adult stages. The mouthparts are adapted for piercing. Like most arachnids, mites breathe by means of tracheae (small tubes opening on the surface of the body), and they live in both aquatic and terrestrial habitats. Many are animal parasites; some, which subsist on vegetation, produce galls on plants. They are economically and medically injurious, because they carry diseases affecting livestock and humans.
Among the most important mites are the chigger and the itch mite. The follicle mites, which infest human hair follicles and sebaceous glands, are about 0.025 cm (about 0.01 in) long. The bird mites infest the skins of birds; the chicken mite attacks domestic poultry and produces a form of dermatitis in humans. More than 100 species of freshwater mites inhabit United States lakes and rivers; these animals have fringed legs that they use in swimming. Among other common mites are the so-called red spiders, or spider mites, which spin spiderlike webs; feeding on the undersides of leaves, they destroy many types of plants.
Scientific classification: Mites belong to the order Acari. Chiggers make up the family Trombiculidae. Itch mites belong to the family Sarcoptidae. Follicle mites belong to the family Demodicidae. Bird mites belong to the family Dermanyssidae. The chicken mite is classified as Dermanyssus gallinae. Freshwater mites belong to the family Hydrachnidae. Red spiders, or spider mites, make up the family Tetranychidae.