Mites
These form a group of animals related to the true Spiders, but differing from them in their very small size, and in having the abdomen closely united with the front part of the body, instead of being joined to it by a narrow stalk. Most Mites have six jointed legs when young, and eight when full-grown; though in a good many the posterior pairs are very small and useless, or may not be present. One group, the Phytopti, or Gall Mites, so far as known, have never more than two pairs of very short legs, on the lower surface of the body, in front. All the true Mites are so small as to render the microscope indispensable in examining them; but, despite their small size, they form an important order of animals, because of their abundance and habits. Many species live on dead or decaying organic matter; others exist as parasites on living animals, especially on insects; and those belonging to Tetranychidae and Phytoptidae are parasites on living plants, and therefore deserve somewhat fuller mention here. The species parasitic on animals may be regarded as mostly useful, since they feed largely on insects; but among them are one or two that are, at certain seasons, very troublesome to gardeners, fruit-pickers, and others. The best known of these is the Harvest Bug (Tetranychus, or Leptus autumnalis), which is of a brick-red colour, and so minute as to be invisible to the naked eye, and which swarms upon bushes and vegetables in the garden, as well as in hay and stubble fields. They feed ordinarily on plant juices, but very readily attack the human skin, especially the skin of women and children; and they are also very troublesome to domestic animals. Wherever a Mite has fixed on the skin, it causes a hard swelling of a red colour, and the place bitten continues to itch greatly for some time. Mites are more abundant during late summer and autumn. They attack some people very severely, others hardly at all. Remedies are as follows: Washing the parts bitten with weak spirits will often prove serviceable in reducing the itching. Sulphur ointment, solution of carbolic acid, and benzine, have also been used, and have been found to give relief. The true Itch Mite (Sarcoptes scabiei) is sometimes very annoying, as it causes intense itching at the wrists and knuckles, where it burrows under the skin. The disease is propagated by contact of healthy with diseased hands, directly, or by handling the same things. It is easily got rid of by personal cleanliness and the use of sulphur ointment.
The Plant Mites belong to the two families Tetranychidae and Phytoptidae. The former group includes eight-legged Mites, which live on leaves and twigs, suck the juices, and often greatly injure the plants thereby. They are usually minute, semi-transparent, and some shade of white, yellow, or pale brick-red. They spin a web on the backs of the leaves. The latter become discoloured, and turn yellowish or grey above, shining dirty-white below. Garden and greenhouse plants often suffer much from their attacks. They are best combated by applications of soft soap and sulphur. Quassia solutions may also be used. The Phytoptidae, or Gall Mites, have long, slender, nearly colourless bodies, and are easily known by their form, their having two pairs of very short legs near the head, and their habit of forming galls on plants. The Mites are very numerous, but are too small and too similar to be easily distinguished; hence, the galls must be employed to recognise the kind of Mites that made them. Cultivated trees and herbs seldom suffer much from the galls on them, so that it is needless here to mention more than the chief forms. These are: 1. The Erineum galls, in the form of patches of velvety hairs on the lower (rarely upper) surface of the leaves; these patches pass from white into rusty brown. They were at one time described as fungi. Examples occur on Apple, Maple, Birch, Beech, &c. 2. Inrolled leaf-margins, with thickened and discoloured tissues, such as may often be seen on leaves of Hawthorn. 3. Blistered spots in the leaves; these sports become brown or black, and are then very conspicuous. Pear leaves are, at times, very much injured in this way; and Elm leaves are yet more frequently infested, though the injury done to them is less. On a careful examination, there is found to be a small hole on the lower surface, about the middle of each discoloured spot, giving passage to the Mites to and from the interior of the leaf. 4. Wart, or Nail Galls, consist of outgrowths from the upper surface of leaves, like warts, about the size of pin-heads, or like small nails, reaching 1/4in. long, and are abundant on Lime, Maple, Willow, and many other trees and shrubs; but, beyond their unsightliness, they usually do little harm to the plants. 5. Bud Galls are buds caused to swell greatly, but to remain unopened, or to from only sickly branches; or, if this continues for some years, it may give rise to knots of diseased branches. The Mites live between the scales of the buds. Much harm is done in this way to Black Currant bushes in some places, and also to Hazel and to Birch. 6. The flower-buds are injured, and become green, and the parts of the flowers are often replaced by green structures, as in reversions to the leaf-type. Campanulas, and a few other cultivated subjects, are liable to this change; but it is more frequent in some wild plants; e.g., in the genus Galium, or the Bedstraws. Yet other forms of Mite Galls might be noted, but they are of no practical moment to gardeners.
It is impossible to reach the Mites, protected as they are in their galls. As a rule, the species that gall the leaves do little practical mischief; but those that gall the buds so spoil the appearance of some plants as to render their destruction desirable. The only certain method is to collect the plants that bear the young galls, and destroy them before the exit of the Mites. Plants (e.g., Currants) badly affected with Bud Galls should be uprooted and burned, and the ground allowed to remain clear of the same plants for a year or two at least.