Trombicula is a genus of harvest mites (also known as red bugs, scrub-itch mites, berry bugs or, in their larval stage, as chiggers or chigoe) in the Trombiculidae family. 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 0.4 mm (1/100 of an inch) and have a chrome-orange hue. A common species of harvest mite in Northern America is Trombicula alfreddugesi; in the UK the most prevalent harvest mite is Trombicula autumnalis.
The larval mites feed on the skin cells, but not blood, of animals, including humans. The six-legged parasitic larva feeds on a large variety of creatures, including humans, rabbits, toads, box turtles, quail, and even some insects. After crawling onto their host, 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.
After feeding on their hosts, the larvae drop to the ground and become nymphs, then mature into adults, which have 8 legs and are harmless to humans. In the post-larval stage, they are not parasitic and feed on plant materials. The females lay 3–8 eggs in a litter, usually on a leaf or under the roots of a plant, and die by autumn.
Harvest mites are found throughout the world. In Europe and North America, they tend to be more prevalent in the hot and humid parts. In the more temperate regions, they are found only in the summer (in French, harvest mites are called Aoûtat, after août, August; Vendangeon, after vendange, harvest; or Rouget, after rouge, red). In the United States, they are found mostly in the southeast, the south, and the Midwest. They are not present, or barely found, in far northern areas, in high mountains and in deserts. They live in forests and grasslands, and are also found in low, damp areas where vegetation is rank, such as woodlands, berry patches, orchards, along lakes and streams, and even in 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 are heaviest. They can also be found in Spanish Moss. Brought into homes and used for decoration, they become easier to attach to humans.
The genus Trombicula has 16 species recorded from North America:
- Trombicula acuitlapanensis (A. Hoffmann, 1957)
- Trombicula alfreddugesi
- Trombicula autumnalis (Shaw)
- Trombicula boneti (A. Hoffmann, 1952)
- Trombicula formicarum (Berlese, 1910)
- Trombicula geniticula
- Trombicula halidasys
- Trombicula imperfecta (Brennan & Jones, 1954)
- Trombicula jamesoni (J. M. Brennan, 1948)
- Trombicula jonesae (J. M. Brennan, 1952)
- Trombicula nagayoi
- Trombicula patrizii (Valle, 1952)
- Trombicula pumilis
- Trombicula spinosa
- Trombicula tecta
- Trombicula zeta
- The World Book Encyclopedia, 2000 ed.
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