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Trombiculidae

life science Maturity 11-13 Next article →

Trombiculidae is a family of tiny mites found all over the world. In North America, people often call them chiggers. In Britain, they are known as harvest mites. They also go by names like berry bugs, bush-mites, or red bugs. These mites are nearly microscopic. They measure about 400 micrometers, which is only 1/60 of an inch. Most of them have a bright chrome-orange color. While they are very small, they play a big role in their environments.

Trombiculid mite larvae attached to human skin
Trombiculid mite larvae attached to human skin

The life cycle of a trombiculid mite consists of four distinct stages. It begins as an egg, which is usually laid on a leaf or among plant roots. After about six days, a non-feeding prelarva emerges. This prelarva then grows into the larval stage. After feeding, the larva drops to the ground to become a nymph. The nymph stage includes three phases: the protonymph, the deutonymph, and the tritonymph. The protonymph is an inactive transitional stage. The deutonymph is active and grows an extra pair of legs to reach a total of eight. Finally, the mite matures into an adult.

Harvest mite cycle
Harvest mite cycle

Only the larval stage of the Trombiculidae is parasitic. These six-legged larvae seek out animal hosts to feed. They crawl onto animals like humans, rabbits, toads, box turtles, and quail. They even feed on some insects. The larvae do not actually bite or suck blood like many people assume. Instead, they inject digestive enzymes into the host's skin. These enzymes break down the skin cells. This process creates a hardened tube made of dead cells called a stylostome. The larva then uses this tube to suck up the digested tissue.

Chigger bite
Chigger bite

This feeding process can cause a condition called trombiculosis. This is the rash or infestation caused by the larvae. When the enzymes interact with the skin, they cause intense irritation. This often results in red papules, which are small pimple-like bumps. It can also cause hives, dermatitis, or skin lesions on sun-exposed areas. For humans, the intense itching often does not start until 24 to 48 hours after the larva has already detached. The red welts are not places where the mite laid eggs. Most of these itchy welts heal on their own within one to two weeks.

TrombiculosisSores
TrombiculosisSores

History shows that humans have been aware of these mites for centuries. References to chiggers go back as far as sixth-century China. In 1733, the first recognition of these mites in North America occurred. In 1758, the scientist Carl Linnaeus described a single species named Acarus batatas. Much of our modern scientific understanding came from studies conducted during and after World War II. In 1944, Henry Ellsworth Ewing first described Trombiculidae as an independent family. His work helped scientists organize the different subfamilies and genera within the group.

Different species of mites live in different parts of the world. In North America, the most familiar species is Trombicula alfreddugesi. It lives from the Atlantic coast to the Midwest and southward into Mexico. In the United Kingdom, the most common species is Neotrombicula autumnalis. This mite is found from Western Europe to Eastern Asia. In Australia, a species called Trombicula hirsti is known as the scrub-itch mite. These mites prefer warm and humid regions. They are less common in deserts, high mountains, or far northern areas.

Harvest mite cycle
Harvest mite cycle

While most chiggers are just a nuisance, some can be dangerous. In East Asia and the South Pacific, the species Leptotrombidium deliense is a serious pest. This mite can carry a bacterium called Orientia tsutsugamushi. This bacterium causes a disease known as scrub typhus. This illness can cause fever, headache, muscle pain, and gastrointestinal symptoms. Without medical treatment, scrub typhus can be fatal. This happens through transovarial transmission, where the bacteria are passed from parent to offspring. This connection shows how tiny organisms can impact large-scale human health.

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File:Harvest mite cycle.svg
Harvest mite cycle.svg
File:Chigger bite.svg
Chigger bite.svg
File:TrombiculosisSores.jpg
TrombiculosisSores.jpg
File:Trombiculid mite larvae attached to human skin.jpg
Trombiculid mite larvae attached to human skin.jpg
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