The order of mites and ticks, in the class Arachnida; easily distinguished by a false head (gnathasoma) that has mouth parts, and by a lack of distinct separation between the cephalothorax and the abdomen.

The Acarina is the most important order of the Arachnids, because in this group are found a number of pests of both plants and animals. The Acarina may be separated from other Arachnida by the sac-like body with the abdomen not distinctly segmented and broadly joined to the cephalothorax. Mouthparts are for piercing and sucking blood.

Mites are generally quite small, many of them being microscopic. The number of species is indicted to be quite large and many of these individual species are very abundant. Both plants and animals are attacked. Some are predators or parasites and others are scavengers. They may be found in the soil, rubbish, plant galls, under stones and bark, and in both fresh and salt water.

Most species deposit eggs; however, a few are ovoviviparous; such as, the straw itch mite (Pyemotes ventricosus). A six-legged larva is hatched from the egg. After a period of feeding, the larva molts into a nymph with eight legs. The nymph feeds and molts one or more times before the adult stage is reached. The adult may be differentiated from the nymph by the presence of a genital pore.