Trombiculidae
Trombiculidae (/trɒmbɪˈkjuːlɪdiː/); commonly referred to in North America as chiggers and in Britain as harvest mites, but also known as berry bugs, bush-mites, red bugs or scrub-itch mites, are a family of mites.[3] Chiggers are often confused with jiggers – a type of flea. Several species of Trombiculidae in their larva stage bite their animal or human host and by embedding their mouthparts into the skin cause "intense irritation"[4] or "a wheal, usually with severe itching and dermatitis".[5][6][7]
Trombiculidae live in forests and grasslands and are also found in the vegetation of low, damp areas such as woodlands, berry bushes, orchards, along lakes and streams, and even in drier places where vegetation is low, such as lawns, golf courses, and parks.[8] They are most numerous in early summer when grass, weeds, and other vegetation are heaviest. In their larval stage, they attach to various animals, including humans, and feed on skin, often causing itching. These relatives of ticks are nearly microscopic, measuring 400 µm (1/60 of an inch) and have a chrome-orange hue.[9][10] There is a marked constriction in the front part of the body in the nymph and adult stages. The best known species of chigger in North America[11] is the hard-biting Trombicula alfreddugesi of the Southeastern United States, humid Midwest[12] and Mexico. In the UK, the most prevalent harvest mite is Neotrombicula autumnalis, which is distributed through Western Europe to Eastern Asia.[13]
Trombiculid mites go through a lifecycle of egg, larva, nymph, and adult.[14] The larval mites feed on the skin cells of animals. The six-legged parasitic larvae feed on a large variety of creatures, including humans, rabbits, toads, box turtles, quail, and even some insects. After crawling onto their hosts, they inject digestive enzymes into the skin that break down skin cells. They do not actually "bite", but instead form a hole in the skin called a stylostome and chew up tiny parts of the inner skin, thus causing severe irritation and swelling. The severe itching is accompanied by red, pimple-like bumps (papules) or hives and skin rash or lesions on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin.[15]
After feeding on their hosts, the larvae drop to the ground and become nymphs, then mature into adults, which have eight legs and are harmless to humans. In the postlarval stage, they are not parasitic and feed on plant material. The females lay three to eight eggs in a clutch, usually on a leaf or under the roots of a plant, and die by autumn.[15]
Trombiculidae, from Greek τρομειν ("to tremble") and Latin culex, genitive culicis ("gnat" or "midge"), was first described as an independent family by Henry Ellsworth Ewing in 1944.[16] Then, when the family was first described, it included two subfamilies, Hemitrombiculinae and Trombiculinae. Womersley added another, Leeuwenhoekiinae, which at the time contained only Leeuwenhoekia. Later, he erected the family Leeuwenhoekiidae for the genus and subfamily, having six genera; they have a pair of submedian setae present on the dorsal plate.[17]
References to chiggers, however, go as far back as sixth-century China, and by 1733, the first recognition of trombiculid mites in North America was made. In 1758, Carl Linnaeus described a single species, Acarus batatas (now Trombicula batatas). However, most information about chiggers came from problems that arose during and after World War II.[18]
