MITE. Mites (Acariña) are minute creatures which form a large division of the Arachnida, distinguished by the absence of any constriction between the céphalothorax and abdomen. Linnaeus included all in the single genus Acarus. They are now divided into several families (mostly containing numerous genera), viz., Trombidiidx (harvest mites), usually scarlet specks seen running on stones, grass, &c, in hot weather ; Tetra-nychi, which, although not bright red, are the red spider of our green-houses, and are distinguished by feet with knobbed hairs ; Bdellidx, long-snouted mites with an-tenniform palpi ; Cheyletidx (fig. 1), the so-called book mites,ferocious, predatory little beings, quite unconnected with books ; Hydrachnidx, freshwater mites with swimming legs, mostly beautiful creatures of brilliant colours; Limnocaridee, crawling freshwater or mud mites; Hcdicaridx, chiefly marine ; Gamasidx, hard-skinned brown mites often parasitic on insects, and best known by the females, and young of both sexes, found on the common dung beetle (Geotrupes stercorarius) ; Ixodidx, the true ticks, not to be confounded with the sheep-tick, &c, which
Fic. 2. Leiosoma palmicinctum ; nymph,
are wingless flies; Oribalidx, beetle mites, so called from their resemblance to minute beetles (these are never parasitic; they undergo transformations almost as strange as those of insects, many of the immature forms being quaint and beautiful, see fig. 2); Myobiadx, bizarre parasites of the mouse, &c, with peculiar holding claws; Tyroglyphidx, the cheese mites; Analgidx, found on the feathers of birds; Sarcoptidx, the itch mites ; Arctisconidx, the water bears; Demodicidx, found in the sebaceous follicles of the human nose, &c.; and Phytoptidx, the gall mites, which attack the leaves of plants, making tiny gall-like excrescences.
The sexes are distinct individuals; the reproduction is oviparous; the larva is almost always hexapod, though the later stages have eight legs; that answering to the pupa of insects is active, and is called the nymph. The breathing in the first-named eleven families is tracheal, the position of the stigmata varying greatly; in the last-named six families it is by the general body surface. No heart or circulation of the blood is known to exist; the alimentary canal is usually somewhat on the insect type, but with enseal prolongations to the stomach, the reproductive organs often more on the crustacean type. There is generally a single very large nerve-ganglion above the oesophagus, sending nerve-branches to the various parts. The legs have ordinarily five to seven joints, rarely three; the feet are usually terminated by claws or suckers, or both, sometimes by bristles. The mandibles are generally large, oftenest chelate (like a lobster's claw), sometimes style-like piercing organs, and of other forms. The maxilla? vary much: they may be piercing or crushing organs, or may coalesce to form a maxillary lip; there is usually one pair of maxillary palpi, no others. Sometimes there is a lingua, and in the Gamasidx a galea. Antennae are not found.
Mites are distributed all over the known world. They have been found in Franz-Josef's Land and Spitzbergen and in the hottest tropical regions, as well as the temperate zones. Often very similar species come from all parts. They are numerous in amber of the Tertiary epoch.
The best-known species are probably those which injure man or his works, viz., the itch mite, the cheese mite, the so-called harvest-bug, and the red spider. The dog-tick is also well known.
The itch mite (Sarcoptes scabiei, fig. 3) is a minute, almost circular, flattened, colourless creature, with skin covered with wavy wrinkles, and a number of triangular points arising from that of the back; legs short, the two front pairs and the fourth pair in the male terminated by suckers on long stalks, the two hind pairs in the female and third pair in the male having long bristles instead. It is parasitic on human beings: the males and young remain chiefly on the surface of the skin, but are difficult to find; the female burrows under the scarf-skin, causing the intense itching of scabies by the action of her chelate mandibles as she eats her way. A small watery pustule is raised near where the acarus has entered the skin, and others arise; the creature is not found in
The Itch Mite (&0^
. , i . . - scabiei) : female. After Megum.
the pustule, but at the further ' end of a short tunnel which may be half an inch long. The eggs are laid in the tunnel after the acarus has passed; they hatch and multiply rapidly. The disease can be certainly cured ; the usual mode is to rub the whole body with sulphur. ointment, which is best done after a warm bath, allow it to remain on all night, and wash off in the morning. This treatment should be repeated once or twice at intervals of a day or two. Other applications of sulphur, as sulphurous acid, sulphur vapour baths, &c, are efficacious. All clothes which have touched the skin must be disinfected by heat. The disease is highly contagious. Most mammals have their peculiar varieties of itch mite.
The cheese mite (Tyroglyphus siro) is an elliptical, fat-bodied, colourless acarus with smooth skin and very long hairs. It breeds in thousands in old cheese, flour, grain, &c, and does much damage. There are numerous allied species; some belonging to the genus Glyciphagus are elegantly ornamented with plumes or leaf-like hairs.
The red-spider (Tetranychus telarius) attacks the leaves of plants or trees, and is a great pest in green-houses. It spins a slight web on the surface of the leaves, and lives in companies on the web; it is of a rusty red or brown.
The harvest bugs, thought by some writers to be a species, and by them called Leptus autumncdis, are simply the larvae of several species of Trombidium. They are predatory, but will attach themselves temporarily to the human skin, and produce the violent itching felt on the lower parts of . the legs after walking through dry grass in autumn. On inspection with a glass the creature may be seen as a minute scarlet point. A drop of benzine will probably get rid of the intruder.
The dog tick, like the harvest-bug, is not really parasitic on mammals, though it attaches itself temporarily; its ordinary food may probably be vegetable. (A. D. M.)
The above article was written by: A. D. Michael, F.R.M.S.