Trombiculidae
| Harvest mite | |
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| Genus: | Trombicula
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Harvest mites (genus Trombicula; also known as red bugs, trombiculid mites, scrub-itch mites, berry bugs or, in their larval stage, as chiggers) are mites in the family Trombiculidae that live in forests and grasslands. In their larval stage they attach to various animals including humans and feed on skin, often causing itching. These relatives of spiders 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.
Life cycle
Harvest mite larvae are small, red immatures between the egg and nymph stages, which have not yet become adult mites. They are usually microscopic. The larvae often live in berry patches, tall grass and weeds, woodland edges, pine straw, leaves, and treebark, or in typical habitats of their hosts (especially rodents).
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 and chew up tiny parts of the inner skin, thus causing severe irritation and swelling. The severe itching is accompanied with red pimple-like bumps (papules) or hives and skin rash or lesion on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin. Chiggers are known for spreading from host to host.
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 300-8,000 eggs in a litter, usually on a leaf or under the roots of a plant, and die by autumn.
Myth versus fact
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Contrary to popular belief, the larvae do not burrow deep into the skin and live there, and neither do coverings such as fingernail polish kill the chigger per se. Rather, the larvae pierce the skin and inject powerful enzymes that digest cellular contents, which become liquified and are consumed by the larvae.
Another myth is that application of malt liquor kills the chiggers or helps with symptoms. This method serves only to cause great burning pain and discomfort to the victim.
Chiggers as disease vectors
Although the harvest mite chigger usually does not carry diseases in North American temperate climates, the mites are considered a dangerous pest in East Asia and the South Pacific because they often carry scrub typhus, which is known alternatively as the Japanese river disease, scrub disease, or tsutsugamushi. The mites usually are infected by the disease by their infected rodent hosts. The disease is transmitted to the next generation of offspring by breeding mites. Symptoms of scrub typhus in humans include fever, headache, muscle pain, cough, and gastrointestinal symptoms.
The North American genus and species can cause severe illness in children. This only occurs when the infestation is particularly heavy. Symptoms include a hallucinatory sense of floating outside one's body, fatigue, fever and general malaise.
Treatment and prevention
If you have been bitten by chiggers, try to not scratch the affected regions. Scratching could scrape off chigger larvae, but it may also cause increased irritation by breaking the skin and leaving it vulnerable to a more serious infection. The most effective way of removing chiggers is by taking a hot shower and washing the affected areas with mildly hot water and soap, as soon as possible after exposure or possible exposure (an Epsom salt bath may help alleviate pruritus). Once symptoms appear, it may be too late to prevent further bites. Taking a hot bath when already covered with chigger bites may in fact be very uncomfortable and increase itching symptoms. Do not rub and scratch the skin aggressively, but instead gently but firmly rub the irritated skin with warm soapy water. A covering to reduce air exposure over the itchy area, such as calamine lotion, petroleum jelly, or baby oil, may help relieve the pain, but they do not cure the bites. The application of a small drop of finger nail polish (usually clear nail polish) is one of the most popular remedies and is claimed to reduce itching and dry the itchy sores in the fewest number of days; however, this practice may be based on the fact that people sometimes mistaken the red dot in the middle of the bite as the chigger itself (the chigger is long gone), and the misconception that it has burrowed into the skin, and are attempting to "suffocate" the chigger by coating their bites with Vaseline or nail polish, or some other air-inhibiting seal. Rubbing alcohol is not recommended and it is very painful and no more effective than other measures.
Chiggers seem to affect warm covered areas of the body more than drier areas. Thus the sock covered ankles, shoe covered feet, behind the knees, and crotch areas should be carefully cleaned. Special attention should be given to small children, as areas higher in the body (chest, back, waist-band, and under-arms) may be affected more easily than in adults, since children are shorter and may more likely than adults come in contact with low-lying vegetation and dry grass where chiggers thrive.
Clothing, especially the pants and socks should be immediately discarded after returning from areas where exposure may have occurred, especially with children. The person should immediately shower washing carefully the ankles, feet, and behind the knees and under the arms and chest in children especially.
To avoid being afflicted by chiggers, always wear tight weave, protective clothing and long pants. Spray insect repellent on your skin for further protection. Application of repellent to the shoes and lower pants is helpful. Staying on trails, roads, or paths can help prevent you from meeting chiggers, ticks, spiders, snakes, and other nuisances and dangers.
Dusting sulfur is used commercially for mite control and can be used to control chiggers in yards. The dusting of shoes, socks and pants legs with sulfur can be highly effective in repelling chiggers.
People who pick wild blueberries in the summer have traditionally been very vulnerable to chigger bites. These people used to apply deodorant soap and let dry on the skin without rinsing of the arms and legs to help prevent bites.
Another helpful avoidance is to recognize the chigger habitat to avoid exposure in the first place. Chiggers in North America thrive late in summer, in dry tall grasses and other thick, unshaded vegetation.
Insect repellents containing one of the following active ingredients are recommended: DEET, Catnip oil extract - Nepetalactone, Citronella or eucalyptus oil extract.
See also
References
- The World Book Encyclopedia, 2000 ed.
- Encyclopædia Britannica, 2005 ed. Accessed with paid subscription.
- Tideland Treasure: The Naturalist's Guide to the Beaches and Salt Marshes of Hilton Head Island and the Southeastern Coast, Revised Edition, by Todd Ballantine.