MITE, a name applied to an order of small Arachnida, and to a coin of slight value. The coin was originally a Flemish copper coin worth one-third or, a smaller fraction of the Flemish penning, penny. It is an expression in English for a coin of the smallest value, from its use in Mark xii., 43.
In zoology, "mite" is the name for minute members of the class Arachnida (q.v.), which, with the ticks (q.v.), constitute the order Acari. The word "mite," however, is merely a popular term and does not connote a natural assemblage. Mites are spread from the arctic to the antarctic hemisphere, and inhabit land, fresh water and the sea. Many are permanent parasites ; others for part of their life only. The largest species reach half an inch in length; while the smallest, the most diminutive Arthropoda, are invisible to the naked eye.
Mites are divided into a number of families. The Bdellidae (Bdella) are free-living with long antenniform palpi. The large tropical forms above mentioned belong to the genus Trombidium of the family Trombidiidae. They are covered with crimson velvety hairs. The legs are adapted for crawling and the palpi are raptorial. They are non-parasitic in the adult ; but immature individuals of a British species (Microtrombidium Autumnale) are parasitic. (See HARVEST BUG.) The Tetranychidae are related to the last. A well-known example, Tetranychus telarius, spins webs and is sometimes called the money spider. The fresh-water Hy drachnidae are generally red or green and globular in shape. Their legs are furnished with long hairs for swimming. The red ap pears to be a warning colour. The marine Halacaridae creep on seaweeds and zoophytes. The Gamasidae are free-living with a thick exoskeleton, and allied to the ticks (q.v.). The Oribatidae or beetle-mites are non-parasitic, and go through remarkable meta morphoses. The Sarcoptidae are mostly parasitic. Some, how ever, live in decaying substances, the best known being the cheese mite (Tyroglyphus siro). An allied species (T. entomophagus) damages collections of insects by destroying the specimens. They may be exterminated by benzine.
The mites are parasitic upon mammals and birds. They belong to the four families, Gamasidae, Trombidiidae (vide supra), Sar coptidae and Demodicidae. Most of the Gamasidae are free-living. The family, however, contains an aberrant genus, Dermanyssus, of which one species, "red-mite," D. gallinae, is found in f owl houses, dovecotes and bird-cages. During the day they lurk in
cracks and emerge at night. They do much damage to the birds by sucking their blood and by depriving them of rest. Birds are also attacked by many species of Sarcoptidae (Pterolichus and Analges) living on and between the barbules of the feathers. They are apparently harmless. Epidermoptes occur on diseased fowls and live on the skin at the base of the feathers where they cause an accumulation of yellowish scales. Cytolechus lives in the con nective tissue round the respiratory organs, or in the air sacs. They also penetrate to certain internal organs, and give rise to tubercle-like nodules.
The cutaneous mites mentioned above, merely suck the blood or feed upon the feathers, scurf and desquamating epidermis. Some species, however, give rise to a contagious disease known as scabies or mange. These mites belong to the Sarcoptidae and Demodicidae. A variety of species are responsible for Sarcoptic mange, Sarcoptes mutans producing it in the feet of birds.
Feather scabies of poultry is caused by S. laevis. Three genera of Sarcoptidae, namely Sarcoptes, Chorioptes and Psoroptes cause mange or scabies in mammals, the mange produced by Sarcoptes being the most serious, because the females of the species scabiei, burrow beneath the skin and are more difficult to kill. Their multiplication is very rapid. The numerous forms de scribed from different mammals are probably all merely temporary varieties of a single species. Mange, if taken in time, can be cured by applications of sulphur ointment. Demodex folliculorum gives rise to "Demodecic or follicular mange," which is difficult to cure on account of the deep situation of the parasites. These infest the hair follicles and sebaceous glands in man and other animals. They differ from those previously noticed in the reduction of their legs and the elongation of the abdomen. They occur on domesti cated animals, as well as on mice and bats.
The family Eriophyidae or gall-mites produce in plants results analogous to those produced in animals by Sarcoptidae and Demo dicidae. As in the Demodicidae the abdomen is elongate, but the Eriophyidae differ from all other mites in having lost the last two pairs of legs. The best known of the excrescences or galls which they produce are the nail-galls of the lime caused by Eriophyes tiliae. Many species have been described. They inflict consider able loss upon fruit-growers by destroying the buds of the trees.