Mites belong to the class of animals known as Arachnida, which are closely related to insects. Spiders and scorpions also belong in this group. Mites are small creatures, usually possessing four pairs of legs when mature, and the body is not divided into three divisions as in the case of insects. The greenhouse red-spider (Tetranychus bimaculatus) is one of the most common and injurious species. It occurs on a wide variety of plants grown under glass and also out-of-doors on the foliage of many wild and cultivated plants. It is about 1/50in. long and varies in color from yellow through orange to brown and dark green, often with a darker spot on each side of the body. It spins a very delicate silken web-like nest over its breeding-ground. It can be killed on the foliage of plants grown in the open with soap solution, dusting with sulfur, and hydrated lime, or by using a flour-paste spray. In greenhouses, it is best controlled by repeated spraying with water, using much force and little water to avoid drenching the beds.

The clover mite (Bryobia pratensis) is a minute, spider-like, oval, reddish brown mite about 3/100inch in length with long front legs. It attacks the foliage of many fruit and forest trees as well as clover and grasses. The tiny, round, reddish eggs often occur in great numbers on the bark of trees in winter giving the branches a reddish color. It may be controlled by the same treatment as for red-spider. In addition, the eggs may be killed with a lime-sulfur solution while the trees are dormant.

The pear-leaf blister-mite (Eriophyes pyri) differs from most other mites in having only two pairs of legs and in its elongate body. The mite is only 1/125inch in length; it burrows in the tissue of the leaf, causing blister-like galls. The eggs are laid within the gall, and some of the mites when mature leave through a small opening and migrate to new leaves. The mature mites hibernate under the bud-scales. This pest is controlled by applications of lime-sulfur or miscible oils while the trees are dormant.

A cross section of spreading board in front of the cleat d, in Fig. 1321.

Fig. 1322. A cross-section of spreading board in front of the cleat "d," in Fig. 1321.