But few naturalists have busied themselves with the study of mites. The honored names of Hermann, Von Heyden, DugÉs, Dujardin and Pagenstecher, Nicolet, Koch and Robin, and the lamented ClaparÈde of Geneva, lead the small number who have published papers in scientific journals. After these, and except an occasional note by an amateur microscopist who occasionally pauses from his "diatomaniacal" studies, and looks upon a mite simply as a "microscopic object," to be classed in his micrographic Vade Mecum with mounted specimens of sheep's wool, and the hairs of other quadrupeds, a distorted proboscis of a fly, and podura scales, we read but little of mites and their habits. But few readers of our natural history text-books learn from their pages any definite facts regarding the affinities of these humble creatures, their organization and the singular metamorphosis a few have been known to pass through. We shall only attempt in the present article to indicate a few of the typical forms of mites, and sketch, with too slight a knowledge to speak with much authority, an imperfect picture of their appearance and modes of living.

Mites are lowly organized Arachnids. This order of insects is divided into the Spiders, the Scorpions, the Harvestmen and the Mites (Acarina). They have a rounded oval body, without the usual division between the head-thorax and abdomen observable in spiders, the head-thorax and abdomen being merged in a single mass. There are four pairs of legs, and the mouth parts consist, as seen in the adjoining figure of a young tick (Fig. 142, young Ixodes albipictus), of a pair of maxillÆ (c), which in the adult terminates in a two or three-jointed palpus, or feeler; a pair of mandibles (b), often covered with several rows of fine teeth, and ending in three or four larger hooks and a serrated labium (a). These parts form a beak which the mite or tick insinuates into the flesh of its host, upon the blood of which it subsists. While many of the mites are parasitic on animals, some are known to devour the eggs of insects and other mites, thrusting their beaks into the egg, and sucking the contents. We have seen a mite (Nothrus ovivorus, Fig. 143) busily engaged in destroying the eggs of a moth like that of the Canker worm, and Dr. Shimer has observed the Acarus? malus sucking the eggs of the Chinch bug. I have also observed another mite devouring the Aphides on the rose leaves in my garden, so that a few mites may be set down as beneficial to vegetation. While a few species are injurious to man, the larger part are beneficial, being either parasitic and baneful to other noxious animals, or more directly useful as scavengers, removing decaying animal and vegetable substances.

The transformations of the mites are interesting to the philosophic zoologist, since the young of certain forms are remarkably different from the adults, and in reaching the perfect state the mite passes through a metamorphosis more striking than that of many insects. The young on leaving the egg have six legs, as we have seen in the case of the Ixodes. Sometimes, however, as, for example, in the larva, as we may call it, of a European mite, Typhlodromus pyri, the adult of which, according to A. Scheuten, is allied to Acarus, and lives under the epidermis of the leaves of the pear in Europe (while Mr. T. Taylor, of the Department of Agriculture at Washington, has found a species in the pear leaves about Washington, and still another form in peach leaves), there are but two pairs of legs present, and the body is long, cylindrical and in a degree worm-like.

I have had the good fortune to observe the different stages of a bird mite, intermediate in its form between the Acarus and Sarcoptes, or Itch mite. On March 6th, Mr. C. Cooke called my attention to certain little mites which were situated on the narrow groove between the main stem of the barb and the outer edge of the barbules of the feathers of the Downy Woodpecker, and subsequently we found the other forms in the down under the feathers. These long worm-like mites were evidently the young of a singular Sarcoptes-like mite, as they were found on the same specimen of Woodpecker at about the same date, and it is known that the growth of mites is rapid, the metamorphoses, judging by the information which we now possess, occupying usually but a few days.

The young (though there is, probably, a still earlier hexapodous stage) of this Sarcoptid has an elongated, oblong, flattened body, with four short legs, provided with a few bristle-like hairs, and ending in a stalked sucker, by aid of which the mite is enabled to walk over smooth, hard surfaces. The body is square at the end, with a slight median indentation, and four long bristles of equal length. They remained motionless in the groove on the barb of the feather, and when removed seemed very inert and sluggish. A succeeding stage of this mite, which may be called the pupal, is considerably smaller than the larva and looks somewhat like the adult, the body having become shorter and broader. The adult is a most singular form, its body being rudely ovate, with the head sunken between the fore legs, which are considerably smaller than the second pair, while the third pair are twice as large as the second pair, and directed backwards, and the fourth pair are very small, not reaching the extremity of the body, which is deeply cleft and supports four long bristles on each side of the cleft, while other bristles are attached to the legs and body, giving the creature, originally ill-shapen, a haggard, unkempt appearance. The two stigmata or breathing pores open near the cleft in the end of the body, and the external opening of the oviduct is situated between the largest and third pair of legs. No males were observed. In a species of Acarus (Tyroglyphus), somewhat like the Cheese mite, which we have alive at the time of writing, in a box containing the remains of a Lucanus larva, which they seem to have consumed, as both young and old are swarming there by myriads, the young are oval and like the adults, except that they are six-legged, the fourth pair growing out after a succeeding moult.

Such is a brief summary of what has been generally known regarding the metamorphoses of a few species of mites. In a few kinds no males have been found; the females have been isolated after being hatched, and yet have been known to lay eggs, which produced young without the interposition of the males. This parthenogenesis has been noticed in several species.

These insects often suddenly appear in vast numbers on various articles of food and about houses, so as to be very annoying. Mr. J. J. H. Gregory, of Marblehead, Mass., has found a mite allied to the European species here figured (Fig. 144) very injurious to the seeds of the cabbage, which it sucked dry. This is an interesting form, and we have called it Cheyletus seminivorus It is of medium size, and especially noticeable from the tripartite palpi, which are divided into an outer, long, curved, claw-like lobe, with two rounded teeth at the base, and two inner, slender lobes pectinated on the inner side, the third innermost lobe being minute. The beak terminates in a sharp blade-like point.

We have received a Cheyletus-like mite, said to have been "extracted from the human face" in New Orleans. The body is oblong, square behind; the head is long and pointed, while the maxillÆ end in a long, curved, toothed, sickle-like blade. That this creature has the habits of the itch mite is suggested by the curious, large, hair-like spines with which the body and legs are sparsely armed, some being nearly half as long as the body. These hairs are covered with very fine spinules. Those on the end of the body are regularly spoon-shaped. These strange hairs, which are thickest on the legs, probably assisted the mite in anchoring itself in the skin of its host. We have read no account of this strange and interesting form. It is allied to the Acaropsis Mericourti which lives in the human face.

A species, "apparently of the genus Gamasus," according to Dr. Leidy, has been found living in the ear (at the bottom of the external auditory meatus, and attached to the membrana tympani) of steers. "Whether this mite is a true parasite of the ear of the living ox, or whether it obtained access to the position in which it was found after the death of the ox in the slaughter house, has not yet been determined."

We will now give a hasty glance at the different groups of mites, pausing to note those most interesting from their habits or relation to man.

The most highly organized mite (and by its structure most closely allied to the spider) is the little red garden mite, belonging to the genus Trombidium, to which the genus Tetranychus is also nearly related. Our own species of the former genus have not been "worked up," or in other words identified and described, so that whether the European T. holosericeum Linn. is our species or not, we cannot tell. The larvÆ of this and similar species are known to live parasitically upon Harvestmen (Phalangium), often called Daddy-long-legs; and upon Aphides, grasshoppers and other insects. Mr. Riley has made known to us through the "American Naturalist" (and from his account our information is taken), the habits of certain young of the garden mite (Trombidium) which are excessively annoying in the Southwestern States. The first is the Leptus? Americanus (Fig. 145), or American Harvest mite. It is only known as yet in the larval or Leptus state, when it is of the form indicated in the cut, and brick red in color. "This species is barely visible with the naked eye, moves readily and is found more frequently upon children than upon adults. It lives mostly on the scalp and under the arm pits, but is frequently found on the other parts of the body. It does not bury itself in the flesh, but simply insinuates the anterior part of the body just under the skin, thereby causing intense irritation, followed by a little red pimple. As with our common ticks, the irritation lasts only while the animal is securing itself, and its presence would afterwards scarcely be noticed but for the pimple which results."

The second species (Fig. 145 b, Leptus? irritans) is also only known in the Leptus stage. It is evidently the larva of a distinct genus from the other form, having enormous maxillÆ and a broad body; it is also brick red. Mr. Riley says that "this is the most troublesome and, perhaps, best known of the two, causing intense irritation and swelling on all parts of the body, but more especially on the legs and around the ankles. Woe betide the person who, after bathing in the Mississippi anywhere in this latitude, is lured to some green dressing-spot of weeds or grass! He may, for the time, consider himself fortunate in getting rid of mud and dirt, but he will afterwards find to his sorrow that he exchanged them for something far more tenacious in these microscopic Harvest-mites. If he has obtained a good supply of them, he will in a few hours begin to suffer from severe itching, and for the next two or three days will be likely to scratch until his limbs are sore.

"With the strong mandibles and the elbowed maxillÆ which act like arms, this mite is able to bury itself completely in the flesh, thereby causing a red swelling with a pale pustulous centre containing watery matter. If, in scratching, he is fortunate enough to remove the mite before it enters, the part soon heals. But otherwise the irritation lasts for two, three or four days, the pustulous centre reappearing as often as it is broken.

"The animal itself, on account of its minute size, is seldom seen, and the uninitiated, when first troubled with it, are often alarmed at the symptoms and at a loss to account for them. Fortunately these little plagues never attach themselves to persons in such immense numbers as do sometimes young or so-called 'seed' ticks; but I have known cases where, from the irritation and consequent scratching, the flesh had the appearance of being covered with ulcers; and in some localities, where these pests most abound, sulphur is often sprinkled during 'jigger' season in the boots or shoes as a protection.

"Sulphur ointment is the best remedy against the effects of either of these mites, though when that cannot be obtained, saleratus water and salt water will partially allay the irritation.

"The normal food of either must, apparently, consist of the juices of plants, and the love of blood proves ruinous to those individuals who get a chance to indulge it. For unlike the true Jigger, the female of which deposits eggs in the wound she makes, these Harvest-mites have no object of the kind, and when not killed by the hands of those they torment, they soon die victims to their sanguinary appetite."

Another Leptus-like form is the parasite of the fly, described by Mr. Riley under the name of Astoma? muscarum (Fig. 146). How nearly allied it is to the European Astoma parasiticum we have not the means of judging.

The European Tetranychus telarius Linn., or web-making mite, spins large webs on the leaves of the linden tree. Then succeed in the natural order the water mites (Hydrachna), which may be seen running over submerged sticks and on plants, mostly in fresh water, and rarely on the borders of the sea. The young after leaving the egg differ remarkably from the adults, so as to have been referred to a distinct genus (Achlysia) by the great French naturalist, Audouin. They live as parasites on various water insects, such as Dytiscus, Nepa and Hydrometra, and when mature live free in the water, though Von Baer observed an adult Hydrachna concharum living parasitically on the gills of the fresh-water mussel, Anodon. The species are of minute size. Collectors of beetles often meet with a species of Uropoda attached firmly to their specimens of dung-inhabiting or carrion beetles. It is a smoothly polished, round, flattened mite, with short, thick legs, scarcely reaching beyond the body.

We now come to the Ticks, which comprise the largest mites. The genus Argas closely resembles Ixodes. Gerstaecker states that the Argas Persicus is very annoying to travellers in Persia. The habits of the wood ticks (Ixodes) are well known. Travellers in the tropics speak of the intolerable torment occasioned by these pests which, occurring ordinarily on shrubs and trees, attach themselves to all sorts of reptiles, beasts and cattle, and even man himself as he passes by within their reach. Sometimes cases fall within the practice of the physician, who is called to remove the tick, which is found sometimes literally buried beneath the skin. Mr. J. Stauffer writes me, that "on June 23d the daughter of Abraham Jackson (colored), playing among the leaves in a wood, near Springville, Lancaster County, Penn., on her return home complained of pain in the arm. No attention was paid to it till the next day, when a raised tumor was noticed, a small portion protruding through the skin, apparently like a splinter of wood. The child was taken to Dr. Morency, who applied the forceps, and after considerable pain to the child, and labor to himself, extracted a species of Ixodes, nearly one-quarter of an inch long, and of an oval form and brown mahogany color, with a metallic spot, like silver bronze, centrally on the dorsal region." This tick proved, from Mr. Stauffer's figures, to be, without doubt, Ixodes unipunctata. It has also been found in Massachusetts by Mr. F. G. Sanborn.

Another species is the Ixodes bovis (Fig. 147), the common cattle tick of the Western States and Central America. It is very annoying to horned cattle, gorging itself with their blood, but is by no means confined to them alone, as it lives indifferently upon the rattlesnake, the iguana, small mammals and undoubtedly any other animal that brushes by its lurking-place in the forest. It is a reddish, coriaceous, flattened, seed-like creature, with the body oblong oval, and contracted just behind the middle. When fully grown it measures from a quarter to half an inch in length. We have received it from Missouri, at the hands of Mr. Riley, and Mr. J. A. McNiel has found it very abundantly on horned cattle on the western coast of Nicaragua.

We now come to the genus Acarus (Tyroglyphus), of which the cheese and sugar mites are examples. Some species of Acarian mites have been found in the lungs and blood-vessels, and even the intestinal canal of certain vertebrates, while the too familiar itch insect lurks under the skin of the hand and other parts of the body of certain uncleanly human bipeds.

Many people have been startled by statements in newspapers and more authoritative sources, as to the immense numbers of mites (Acarus sacchari, Fig. 148) found in unrefined or raw sugar. According to Prof. Cameron, of Dublin, as quoted in the "Journal of the Franklin Institute," for November, 1868, "Dr. Hassel (who was the first to notice their general occurrence in the raw sugar sold at London) found them in a living state in no fewer than sixty-nine out of seventy-two samples. He did not detect them in a single specimen of refined sugar. In an inferior sample of raw sugar, examined in Dublin by Mr. Cameron, he reports finding five hundred mites in ten grains of sugar, so that in a pound's weight occurred one hundred thousand of these little creatures, which seem to have devoted themselves with a martyr-like zeal to the adulteration of sugar. They appear as white specks in the sugar. The disease known as grocer's itch is, undoubtedly, due to the presence of this mite, which, like its ally the Sarcoptes, works its way under the skin of the hand, in this case, however, of cleanly persons. Mr. Cameron states that "the kind of sugar which is both healthful and economical, is the dry, large-grained and light-colored variety."

Closely allied to the preceding, is the Cheese mite (Acarus siro Linn.), which often abounds in newly made cheese. Lyonet states that during summer this mite is viviparous. Acarus farinÆ DeGeer, as its name indicates, is found in flour. Other species have been known to occur in ulcers.

We should also mention the Mange insect of the horse (Psoroptes equi, Fig. 149, much enlarged; a, head more magnified). According to Prof. Verrill it is readily visible to the naked eye and swarms on horses afflicted with the mange, which is a disease analogous to the itch in man. It has a soft, depressed body, spiny beneath at the base of the legs and on the thorax. One or both of the two posterior pairs of feet bear suckers, and all are more or less covered with long, slender hairs. This insect may be destroyed by the same remedies as are used for lice and for the human itch. The best remedy is probably a solution of sulphuret of potassium.

The itch insect (Sarcoptes scabiei, Fig. 150) was first recognized by an Arabian author of the twelfth century, as the cause of the disease which results from its attacks. The body of the insect is rounded, with the two hind pair of feet rudimentary and bearing long hairs. It buries itself in the skin on the more protected parts of the body, and by its punctures maintains a constant irritation. Other species are known to infest the sheep and dog. Another singular mite is the Demodex folliculorum (Fig. 151), which was discovered by Dr. Simon, of Berlin, buried in the diseased follicles of the wings of the nose in man. It is a long, slender, worm-like form, with eight short legs, and in the larva state has six legs. This singular form is one of the lowest and most degraded of the order of Arachnids. A most singular mite was discovered by Newport on the body of a larva of a wild bee, and described by him under the name of Heteropus ventricosus. The body of the fully formed female is long and slender. After attaining this form, its small abdomen begins to enlarge until it assumes a globular form, and the mass of mites look like little beads. Mr. Newport was unable to discover the male, and thought that this mite was parthenogenous. It will be seen that the adult Demodex retains the elongated, worm-like appearance of the larva of the higher mites, such as Typhlodromus. This is an indication of its low rank, and hints of a relationship to the Tardigrades and the Pentastoma, the latter being a degraded mite, and the lowest of its order, living parasitically within the bodies of other animals.