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 babesiosis , tick-borne disease caused by a protozoan of the genus Babesia. Babesiosis most commonly affects domestic and wild animals and can be a serious problem in cattle. In most cases the protozoal species is specific to a single host.
..... Click the link for more information. , anaplasmosis anaplasmosis , infectious blood disease in cattle, sheep, and goats, caused by a rickettsia of the genus Anaplasma. The organism parasitizes red blood cells, causing their destruction and producing emaciation, anemia, jaundice, and, occasionally, death.
..... Click the link for more information. ) 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 chitin , main constituent of the shells of arthropods. Chitin, a polysaccharide (see carbohydrate) analogous in chemical structure to cellulose, consists of units of a glucose derivative (N-acetyl-d
..... Click the link for more information. , remain attached to the host for long periods.
Ticks transmit Rocky Mountain spotted fever Rocky Mountain spotted fever, infectious disease caused by a rickettsia. The germ is harbored by wild rodents and other animals and is carried by infected ticks that attach themselves to humans.
..... Click the link for more information. , tularemia tularemia or rabbit fever, acute, infectious disease caused by Francisella tularensis (Pasteurella tularensis). The greatest incidence is among people who handle infected wild rabbits.
..... Click the link for more information. , Lyme disease Lyme disease, a nonfatal bacterial infection that causes symptoms ranging from fever and headache to a painful swelling of the joints. The first American case of Lyme's characteristic rash was documented in 1970 and the disease was first identified in a cluster at
..... Click the link for more information. , equine encephalitis equine encephalitis , infectious disease of horses caused by any of several viruses, four of which—the Eastern, Western, Venezuelan, and St. Louis viruses—can also infect humans.
..... Click the link for more information. , several forms of ehrlichiosis ehrlichiosis , any of several diseases caused by rickettsia of the genus Ehrlichia. Ehrlichiosis is transmitted by ticks. Both human forms tend to develop about nine days after a tick bite.
..... Click the link for more information. , 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 Chelicerata , phylum of the living horseshoe crabs (class Merostomata), the arachnids (class Arachnida), and the sea spiders (class Pycnogonida). Chelicerates are characterized by the absence of antennae and jaws and the presence of feeding structures (chelicera),
..... Click the link for more information. , class Arachnida, order Acarina.
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