Page:The New International Encyclopædia 1st ed. v. 13.djvu/708

MITE. 630 MITE. commensal, making ii»e of the carrier only for transportation; anil in certain ganiasids ( L'ro- poda) the mite in this migratorial stage is at- tached by a thread of hanlened excrement to its host. In some families (as the Trombidiidte) the larval and nymphal stages are attached to vari- ous insects and feed thereon, while the adult is free. In some of the bectle-niites the nymph car- ries on its back old nioltwl skins, egg-sliclls, anil otlicr debris. In these mites there is a consid- erable resting- period while the nymph is chang- ing to the adult, a period when iiuicli of the internal anatomy is entirely changed; and it has been observed that wlien the adult emerges its legs are not withdrawn from the legs of the nymph, but from beneath the body. In the bird- mites there is a transition-form between the liyni]ili and the adult female, known as the nymphal female. The adult male mates with this nymphal form, and when the real adult emerges, an egg, already of considerable size, is seen in her body. Parthenogenesis has been ob- served in a number of mites. As a rule, mites possess no special accessory sexual organs, com- parable to those of spiders, but in some male gamasids the mandibles carry the globule of .sperm cells and insert it in the female vulva. In many species the males have one pair of legs enlarged and modified to act as claspers for hold- ing the female. The eggs are usually deposited singly, but many gall-mites and harvest-mites place them in clusters. H.i!rrs. The habits of mites are very diverge. Host mites ordinarily move quite slowly and de- liberately; very few mites are fitted for leaping. The spinning mites or "little red spiders' (Te- tranychus) produce a tiny thread wherever they go, the accumulated threads of many individuals making a whitish mesh or web. More than one- half of the known mites are jiarasitie, at least during part of their life. The ticks are well known to infest various mammals, birds, and even snakes and turtles. They have mnulli-parts especially lilted for cutting into the skin of the host and sucking up the blood. (See Tick.) One group of the gamasids is parasitic on bats, birds, and small mammals. The bird-mites live upon tlic skin and feathers of birds, but as they feed upon epidermal scales and loose bits of feathers, they do not injure their hosts, but are rather of service in keeping the skin and feath- ers clean. The itch-mites burrow within the skin of man and other mammals. Dtlicr species live in the cellular tissue of birds. A few occur in the tracheal passages of seals, and one has been found living in the lung of a monkey. JIany species feed on living plants, and the gall-mites produce deformations on the leaves and twigs of plants. .Siiifc these gall-mites are invisible to the unaided eye, the deformations were fnrmerly supposed to be fungi. Many of the bcclle-mites feed on fungi, lichens, and other low vegetation. . large number of mites are predneeous and attack other mites and small insects. There is a large family, the water-mites, living in fresh water, sometimes as conmiensals within the gills of bivalve mollusks; another group lives in the oeenn, even at n considerable depth. In recent years investigators have found n number of mites nssoclaterl with ants. In.urie.s. The injuries eatrsed by mites are arranged in two classes: injuries to man and domestic animals, and injuries to cultivated plants and stored food. The most notable of the former class are the ticks. The famous miana hug (if I'ersia is a tick of the genus Argas, which inhabits houses, and the early travelers in tiiose regions declared that its bite or puncture would produce convulsions, delirium, and even death. Specimens kept in Europe, however, have proved to be comparatively harmless. The moubata bug of Africa is a similar tick with a similar reputa- tion. An allied species, the chieken-tiek {Aii/as niinidtd) . iloes considerable damage to poultry in the Southern States. The cattle-tick (llwjpliiliis hovis) is the most injurious of all mites, as it occurs in nearly all warm countries, and is the means of spreading the Texas or Southern cattle fever. The itch-mites that cause a disgusting scaling of the skin were formerly not uncommon, but modern cleanliness has largely abolished them in the case of man. A species known as the sheep seab-mite (I'.ioropIcK communis) 'is the cause of much injury to sheep, both In flesh and CLOVER MITE (Br^obhi pratensis). wool. The red spider (Tetranychus) is a peren- nial source of trouble to greenhouse and out- door plants, while the 'elovcr-mite' is a i)est of fruit trees in the West, and a related form (StignLTiis) injures pineapples in Florida. To the family of cheese or Hour mites ( Tyro- glyphidic) belong a number of injurious species. The true cheese or fiour mites (Tyroglyphus and Alenrobius) feed on a great variety of stored products: cheese, flour, hams, cereals, drugs, seeds, and dried fruits, .lthough they are very small, they multi])ly so rapidly that attacked materials are completely overrun with them in a few days. Some species infest mushroimis and are a serious hindrance to their cultivation. The bulb-mite, m- eueharis-mite ( Khizoglyiihus ) . bur- rows within bulbs and the roots of jdaiits, there- by giving entrance to destructive fungi; the bulbs of lilies and orchids are jiartieularly subject to their ravages. A few species of gall-mites arc of great economic importance, especially the pear- leaf blister-mite { IC rioph i/rx pi/ri). which is n notorious enemy of pear culture in the United States. Certain species of Tarsonemidiv. living in enormous numbers in the heads of grasses, are kown to cause a whitening of the grass, called 'silver-to]).' Comparatively few mites are beneficial to man. One of the harvest-mites is known to destroy the eggs of grassho]i]iers. and various speries of Cheyletus prey on the flour-mites and other in- jurious forms. Several species have been found feeding on scale-insects. Ci.AssiFTrATioN. The mites, formerly all kept in one family, have, in recent years, bicn divided into from ten to thirty families, accordiiii.' to the author. The leading families are the following: