the Tick or Mite, a genus of insects belonging to the order of aptera, or such as have no wings. The acarus has eight legs; two eyes, one on each side of the head; and two jointed tentacula. The female is oviparous. Linnaeus enumerates 35 species; of which some are inhabitants of the earth, some of waters; some live on trees, others among stones, and others on the bodies of other animals, and even under their skin. The description of a few of the most remarkable will here suffice.
1. The fire, or cheese-mite, is a very minute species. To the naked eye, these mites appear like moving particles of dust; but the microscope discovers them to be perfect animals, having as regular a figure, and performing all the functions of life as perfectly, as creatures that exceed them many times in bulk. The principal parts of them are the head, the neck, and the body. The head is small in proportion to the body; and has a sharp snout, and a mouth that opens and shuts like a mole's. They have two small eyes, and are extremely quick-fighting; and when they have been once touched with a pin, you will easily perceive how cunningly they avoid a second touch. Their legs are each furnished at the extremity with two little claws, with which the animal very nicely takes hold of any thing. The hinder part of the body is plump and bulky; and ends in an oval form, from which there issue out a few exceeding long hairs. Other parts of the body are also befet with thin and long hairs. The males and females are easily distinguished in these little animals. The females are oviparous, as the louse and spider; and from their eggs the young ones are hatched in their proper form, without having any change to undergo afterwards. They are, however, when first hatched, extremely minute; and, in their growing to their full size, they cast their skins several times. These little creatures may be kept alive many months between two concave glasses, and applied to the microscope at pleasure. They are thus often seen in coitus, conjoined tail to tail; and this is performed by an incredibly swift motion. Their eggs, in warm weather, hatch in 12 or 14 days; but in winter they are much longer. These eggs are so small, that a regular computation shows, that 90 millions of them are not so large as a common pigeon's egg*. They are very voracious animals, and have often been seen to eat one another. Their manner of eating is by thrusting alternately one jaw
* Baker's Microscope, p. 187. jaw forward and the other backward, and in this manner grinding their food; and after they have done feeding, they seem to chew the cud.—There are several varieties of this species found in different substances besides cheese; as in malt-dust, flour, oatmeal, &c. Those in malt-dust and oatmeal are much nimbler than the cheese-mites, and have more and longer hairs. There are also a sort of wandering mites, which range wherever there is anything they can feed on: They are often seen in the form of a white dust, and are not suspected to be living creatures.—The mite is called by authors, simply, Acarus. It is an animal very tenacious of life, and will live months without food. Mr Arean, Leuenhoek† had one which lived 11 weeks on the point of a pin, on which he had fixed it for examining by his microscope.
2. The sanguifugus. The hinder part of the abdomen is crenated, the scutellum is oval and yellowish, and the beak is trifid. It is a native of America, and sticks so fast on the legs of travellers, sucking their blood, that they can hardly be extracted.
3. The telarius is of a greenish yellow colour. It has a small fitting or weapon, with which it wounds the leaves of plants, and occasions them to fold backward. They are very frequently to be met with in the autumn, inclosed in the folded leaves of the lime-tree.
4. The exulcerans, or itch-acarus, is a very small species: its body is of a figure approaching to oval, and lobated; the head is small and pointed; its colour is whitish, but it has two dusky semicircular lines on the back. It has long fetaceous legs, but the two first are short. It is found in the pustules of the itch: authors in general have supposed that it causes that disease; but others observe, that if this were so, it would be found more universally in those pustules. It is more probable that these only make a proper nidus for it. See, however, the article Ircn.
5. The batatas is of a blood-colour, and a little rough; the fore pair of legs are as long as the body. It inhabits the potatoes of Surinam.
6. The ovinus, or sheep-tick, has a flat body, of a roundish figure, but somewhat approaching to oval, and of a yellowish white colour, and has a single large round spot on the back; the anus is visible in the lower part of the body; the thorax is scarce conspicuous; the head is very small and black; the mouth is bifid; the antennae are of a clavated figure, and of the length of the snout; the legs are short and black. It is common on sheep, and its excrements stain the wool green; it will live in the wool many months after it is shorn from the animal.
7. The coleopterorum, or acarus of insects, is extremely minute: its body is round, reddish, and covered with a firm and hard skin; the head is very small, the neck scarce visible; the legs are moderately long, the anterior pair longer than the others; it has a whitening about the anus. It is frequent on the bodies of many insects, which it infects, as the louse does others; it runs very swiftly: the humble-bee, and many other of the larger insects, are continually infected with it; but none so much as the common black beetle, which has thence been called the lousy beetle.
8. The baccarum, or scarlet tree-mite, is a small species: its body is roundish, and the back not at all flattened, as it is in many others; the skin is smooth, shining, and glossy; and the whole animal seems distended, and ready to burst; the colour is a bright red, but a little dusky on the sides than elsewhere: the head is very small, and the legs short; there is on each side a small dusky spot near the thorax, and a few hairs grow from different parts of the body. It is very common on trees, particularly on the currant, on the fruit of which we frequently see it running.
9. The longicornis, or red stone-acarus, is very small, and of a bright red colour; the body is round, and distended; the head is very small and pointed; the legs are moderately long, and of a paler red than the body: the antennae are much longer than in any other species. It is frequent about old stone-walls and on rocks, and runs very nimbly. See Plate I.
10. The aquaticus is a small species: the body is of a figure approaching to an oval, and the back appears depressed; it is of a bright and strong scarlet colour. The head is small; the legs are moderately long and firm, and are of a paler red than the body. It is common in shallow waters, where it runs very swiftly along the bottom. Its diminutiveness hinders the beauty of its colours from being perceived, as they are not discernible without the microscope.
11. The holofericeus is a small species: its body is roundish, but a little approaching to oval; the back somewhat depressed: it is of a fine scarlet colour, and covered with a velvety down. The head is very small; the eyes are two, and very small; the legs are short and of a paler red, and there is a small black spot near the insertion of the anterior ones. It is very common under the surface of the earth, and sometimes on herbs and among hay. It is supposed to be poisonous if swallowed; but we do not seem to have any certain account of such an effect.
12. The longipes is the largest of the acarus kind: its body is roundish, of a dusky brown on the back, with a dusky spot of a rhomboidal figure near the middle of it; the belly is whitish; the legs are extremely long and slender. On the back part of the head there stands a little eminence, which has on it a kind of double crest, formed as it were of a number of minute spines: the eyes are small and black, and are two in number. It is very common in our pastures towards the end of summer. Ray and Lister call it araneus crysatus longipes; Mouffet, araneus longipes; and, notwithstanding its having but two eyes, it has been almost universally ranked among the spiders.