Trombiculidae

Trombiculidae (/trɒmbɪˈkjuːlɪdiː/), commonly referred to in North America as chiggers and in Britain as harvest mites, and also known as berry bugs, bush-mites, red bugs or scrub-itch mites, are a family of mites. Chiggers are often confused with jiggers, a type of flea. In their larval stage several species of Trombiculidae bite animal hosts to feed on their skin. To do so they embed their mouthparts into the skin, causing irritation. Humans can be hosts.

Trombiculidae live in forests and grasslands and are often found in the vegetation of low, damp areas such as berry bushes, orchards, along lakes and streams, as well as drier places where vegetation is low, such as lawns, golf courses, and parks. They are most numerous in early summer when grass, weeds, and other vegetation is heaviest. They are relatives of ticks and are nearly microscopic, measuring 400 μm (1/60 of an inch) and have a chrome-orange hue. There is a constriction in the front part of the body in the nymph and adult stages. The best known species of chigger in North America is the hard-biting Trombicula alfreddugesi of the Southeastern United States, humid Midwest and Mexico. In the UK, the most prevalent harvest mite is Neotrombicula autumnalis, which is distributed through Western Europe to Eastern Asia.

Trombiculid mites go through a lifecycle of egg, larva, nymph, and adult. The six-legged parasitic larvae feed on a large variety of animals, including humans, rabbits, toads, box turtles, quail, and even some insects. In the larval stage they crawl onto their hosts and 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 digest parts of the inner skin, causing irritation and swelling. The itching is accompanied by red papules (pimple like bumps) or hives, dermititis, and skin rash or lesions on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin.

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 post-larval stages, they are not parasitic and feed on plant material and insects. The females lay three to eight eggs in a clutch, usually on a leaf or among the roots of a plant, and die by autumn.