Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari.

This last type includes the commercially destructive Varroa parasite of honey bees, as well as scabies mites of humans.

The phylogeny of the Acari has been relatively little studied, but molecular information from ribosomal DNA is being extensively used to understand relationships between groups.

[10] Palpigradi False scorpions Ixodida (ticks) Parasitic mites, inc. Varroa Trombidiformes (chiggers, velvet mites, etc) Sarcoptiformes (dust & fur mites, etc) Camel spiders other Arachnids including spiders and scorpions However, a few phylogenomic studies have found strong support for monophyly of Acari and a sister relationship between Acariformes and Parasitiformes,[14][15] although this finding has been questioned, with other studies suggesting that this likely represents a long branch attraction artefact.

This is not a head and does not contain the eyes or the brain, but is a retractable feeding apparatus consisting of the chelicerae, the pedipalps and the oral cavity.

[18] The pedipalps differ between taxa depending on diet; in some species the appendages resemble legs while in others they are modified into chelicerae-like structures.

[27] The circulatory system consists of a network of sinuses and most mites lacks a heart, movement of fluid being driven by the contraction of body muscles.

[30] The sexes are separate in mites; males have a pair of testes in the mid-region of the body, each connected to the gonopore by a vas deferens, and in some species there is a chitinous penis; females have a single ovary connected to the gonopore by an oviduct, as well as a seminal receptacle for the storage of sperm.

They are found in freshwater (e.g. the water mites or Hydrachnidia[35]) and saltwater (most Halacaridae[36]), in the soil, in forests, pastures, agricultural crops, ornamental plants, thermal springs and caves.

[41] When soil is affected by an ecological disturbance such as agriculture, most mites (Astigmata, Mesostigmata and Prostigmata) recolonise it within a few months, whereas Oribatida take multiple years.

Dust mites, which feed mostly on dead skin and hair shed from humans instead of consuming them from the organism directly, evolved from these parasitic ancestors.

[43] Ticks are a prominent group of mites that are parasitic on vertebrates, mostly mammal and birds, feeding on blood with specialised mouthparts.

Varroa destructor attaches to the body of honey bees, and Acarapis woodi (family Tarsonemidae) lives in their tracheae.

[46] Most larvae of Parasitengona are ectoparasites of arthropods, while later life stages in this group tend to shift to being predators.

[48] Among the species that attack animals are members of the sarcoptic mange mites (family Sarcoptidae), which burrow under the skin.

Demodex mites (family Demodecidae) are parasites that live in or near the hair follicles of mammals, including humans.

Some species mount to a high point and adopt a dispersal posture and get carried away by the wind, while others waft a thread of silk aloft to balloon to a new position.

Another strategy is phoresy; the mite, often equipped with suitable claspers or suckers, grips onto an insect or other animal, and gets transported to another place.

The majority are beneficial, living in the soil or aqueous environments and assisting in the decomposition of decaying organic material, as part of the carbon cycle.

[59] House dust mites, found in warm and humid places such as beds, cause several forms of allergic diseases, including hay fever, asthma and eczema, and are known to aggravate atopic dermatitis.

[60] Among domestic animals, sheep are affected by the mite Psoroptes ovis which lives on the skin, causing hypersensitivity and inflammation.

[62] The mite Varroa destructor is a serious pest of honey bees, contributing to colony collapse disorder in commercial hives.

[65] Among the Laelapidae, Gaeolaelaps aculeifer and Stratiolaelaps scimitus are used to control fungus gnats, poultry red mites and various soil pests.