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The Acarina are small to tiny arachnids. The largest (e.g. fully gorged ticks) may reach a length of nearly 25 mm., while the smallest rarely exceed 0.25 mm. in length. The order has many identified species, but specialists admit that this could represent less than 20 percent of those that occur worldwide. Similar to the insects and crustaceans, the species in nature occur in very large numbers. The body is depressed dorsoventrally and serves for adaptation to their mode of life. The head and abdomen are fused, producing a saclike appearance. In some species the cephalothorax may be separated from the abdomen by a groove or furrow. The body may be partially or completely by a shield-like structure. The mouth parts are located on the anterior ventral surface. The eyes are either present or absent; when present they consist of simple convex facet and are generally located on the margin of the scutum or on folds on the ventral surface. The respiratory organs, when present are connected to the exterior by means of spiracles. The spiracles are generally on chitinized plates and may be either singly or in pairs. Tracheae are absent in some species where breathing id directly through the body wall. Sexes are distinct, the males usually smaller than the females. Reproductive organ openings are located on the ventral surface behind the mouthparts. The digestive system is a straight tube usually with many tubular branches. The anal opening may be either on the ventral or dorsal side, but rarely at the posterior.
There are many different habits among the mites. They consume mainly body fluids of their host plants or animals or from decomposing organic matter. Many mites are free-living and predatory, and many are also parasitic. Parasitic mites have a great variety of life styles. For example, the ticks are external parasites of animals, feeding on blood. Some ticks burrow into the skin and cause itching and subsequent infections. Other species are found in the lungs of seals and monkeys. Chiggers are free-living and herbivorous or predaceous as nymphs and adults. Many species attack birds, feeding on their scales and feathers or they may invade the lungs and hollow bones. Some species attack stored food products and pass over to humans working close by. Of great importance are the bloodsucking mites that serve as intermediate hosts of human pathogens.
The identification of mite species is continuously changing, as they are a difficult group to study. The position of body hairs is frequently used for diagnoses. Acarina that are parasitic may be found primarily in the following Suborders and Superfamilies:
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Key References: <medvet.ref.htm>
Banks, N. A. 1915. The Acarina or mites. U.S. Dept. Agr. Rept. 108.
Bishopp, F. C. 1935. Ticks and the role they play in the transmission of diseases. Rept. Smithsonian Inst.
for 1933: pp 389-406.
Bishopp, F. C. & H. L. Trembley. 1945. Distribution of certain North American ticks. J. Parasitology:: 31-1-54.
Bishopp, F. C. & H. P. Wood. 1913. The biology of some North American ticks of the genus Dermacentor. Parasitology
Cooley, R. A. 1942. Determination of Ornithodoros species. In: Symposium on relapsing fevers in the
Americas. Am. Asoc. Adv. Sci. Pub. 18: 77-84.
Ewing, H. E. 1926. Key to the known adult trombiculas (adults of chiggers) of the New World with descriptions
of two new species (Acarina,Trombidoidea) Ent.News 37: 111-13.
Ewing, H. E. 1944. The trombiculid mites (chigger mites) and their relation to disease. J. Parasitology 30:
Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.
Service, M. 2008. Medical Entomology For Students. Cambridge Univ. Press. 289 p