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mite

mite

[mahyt]
mite, small, often microscopic chelicerate that, along with the tick, makes up the order Acarina; it is also related to spiders. The unsegmented mite body is typically oval and compact, although a few, mostly parasites, are elongated and wormlike. There are four pairs of legs. The movable head is attached to the body by a hinge. There are four stages in the life cycle: egg, larva, nymph, and adult.

The thousands of different mite species are worldwide in distribution and occupy diverse habitats, including plant galls, mosses, other animals, and surface litter or upper layers of the soil. One group, the water mites, has returned to an aquatic environment, both fresh- and saltwater. Mites eat plant or animal substances, decaying organisms, and humus, and also infest stored food products such as cheese, meat, grains, and flour. The spider mite, or red spider, which is a mite and not a spider, feeds on plants and is destructive to crops. Many mites are parasitic on other arthropods, on mollusks, or on vertebrates. Mange and scabies mites lay their eggs in the skin and cause irritation in humans and fur-bearing animals. Other species are parasitic on the skin of birds and reptiles, and some live in the respiratory channels of birds and mammals. Chiggers, the larvae of harvest mites, transmit the organism that causes scrub typhus. Fowl mites feed on the blood of poultry.

The larger members of the order Acarina, the ticks, are all parasitic in at least one developmental stage; most parasitize mammals and birds although some have reptilian and amphibian hosts. Tick-borne diseases of livestock (e.g., babesiosis, anaplasmosis) are of great economic significance. An anchoring structure in the tick's mouth enables it to embed its entire head under the skin of the host, where it sucks the host's blood. If a tick is pulled off the host, the head usually remains embedded in the skin. Members of the family (Argasidae) of soft ticks, with a membranous outer covering, hide in crevices and come out at night to suck blood. Hard ticks (family Ixodidae), which have thickened outer plates made of chitin, remain attached to the host for long periods.

Ticks transmit Rocky Mountain spotted fever, tularemia, Lyme disease, equine encephalitis, several forms of ehrlichiosis, and other diseases. Each species needs three different hosts to complete its life cycle. Typically the larval stage will feed on small reptiles, birds, or mammals; the nymph stage will parasitize larger vertebrates; and adults will parasitize large herbivores and livestock. The adult of the ixodid species Ixodes dammini, the vector of Lyme disease in the E United States and Canada, usually chooses deer as its host (I. dammini of all stages will feed on humans). The closely related I. pacificus, which transmits Lyme disease and Rocky Mountain spotted fever in the western states, prefers livestock in the adult stage. Ticks can sometimes harbor more than one disease organism at a time.

Mites and ticks belong in the phylum Chelicerata, class Arachnida, order Acarina.

or red spider

Any plant-feeding mite in the family Tetranychidae, common pests on houseplants and agriculturally important plants. Adult spider mites are tiny, about 0.02 in. (0.5 mm) long, and often red. They spin a loose silk webbing on infested plants. A heavy infestation can cause complete defoliation. Because of their increasing resistance to pesticides, they are difficult to control. One effective control is the use of another, predatory, mite species.

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Red velvet mite (Dinothrombium; magnified about five times)

Any of about 20,000 species of tiny arachnids (subclass Acari, sometimes Acarina or Acarida). Species range from microscopic to 0.25 in. (6 mm) long. Mites live in water and soil, on plants, and as plant and animal parasites. Both parasitic and nonparasitic forms transmit plant and animal diseases. Itch mites (family Sarcoptidae), which burrow into the skin of humans and animals, cause the highly contagious disease scabies. A few species transmit tapeworms to cattle. Grain mites (family Glycyphagidae) damage stored products and irritate the skin of those who handle the products. House dust allergy is caused by species of the common genus Dermatophagoides. Seealso chigger.

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Larva of some 10,000 mite species, ranging in length from 0.004 to 0.6 in. (0.1–16 mm). Some are terrestrial; others live in freshwater or salt water. They may be predators, scavengers, or plant feeders, and some are pests of humans, either as parasites or as carriers of disease. In North America, the common chigger that attacks humans is found from the Atlantic coast to the Midwest and Mexico. The larva penetrates clothing and, once attached to the skin, injects a fluid that digests tissue and causes severe itching. After feeding, the larva drops to the ground and begins to mature.

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Mites, along with ticks, belong to the subclass Acarina (also known as Acari) and the class Arachnida. Mites are among the most diverse and successful of all the invertebrate groups. They have exploited an incredible array of habitats, and because of their small size (most are microscopic) most go totally unnoticed. Many live freely in the soil or water, but there are also a large number of species that live as parasites on plants, animals, and even some that feed on mold.

Some of the plant pests include the so called spider mites (family Tetranychidae), thread-footed mites (family Tarsonemidae), and the gall mites (family Eriophyidae). Among the species that attack animals are members of the Sarcoptic Mange mites (family Sarcoptidae), which burrow under the skin. Demodex mites (family Demodicidae) are parasites that live in or near the hair follicles of mammals, including humans. Perhaps the best-known mite, though, is the house dust mite (family Pyroglyphidae).

Insects may also have parasitic mites. Examples are Varroa destructor which attaches to the body of the honeybee, and Acarapis woodi (family Tarsonemidae), which lives in the tracheae of honey bees. There are hundreds of species of mites associated with other bee species, and most are poorly described and understood. Some are thought to be parasites, while others beneficial symbionts.

There are over 45,000 described species of mites Scientists believe that we have only found 5% of the total diversity of mites. Mites are believed to have existed for around 400 million years.

The scientific discipline devoted to the study of ticks and mites is called acarology.

The tropical species Archegozetes longisetosus is one of the strongest animals in the world, relative to its mass (100 μg): It lifts up to 1182 times its own weight, over five times more than would be expected of such a minute animal (Heethoff & Koerner 2007).

Systematics

In the usual taxonomy, the ticks form one of several superfamilies in the taxon comprising the mites. For the systematics of mites, see Acarina.

Allergy

Mites cause several forms of allergic diseases, including hay fever, asthma and eczema and also aggravates atopic dermatitis. Mites are usually found in warm and humid locations, including beds. It is thought that inhalation of mites during sleep exposes the human body to some antigens which eventually induce hypersensitivity reaction. Dust mite allergens are thought to be among the heaviest dust allergens.

Like most of the other types of allergy, treatment of mite allergy starts with avoidance. There is a strong body of evidence showing that avoidance should be helpful in patients with atopic dermatitis triggered by exposure to mites. Regular washing of mattresses and blankets with hot water can help in this regard. Antihistamines are also useful; Cetirizine, for example, is shown to reduce allergic symptoms of patients.

References

  • & (2007): Small but powerful – The oribatid mite Archegozetes longisetosus Aoki (Acari, Oribatida) produces disproportionate high forces. J. Exp. Biol. 210(17): 3036–3042. (Abstract).

External links

on the UF / IFAS Featured Creatures Web site


                        --Contributions/90.216.217.9 (90.216.217.9) 19:22, 7 October 2008 (UTC)AKABI
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