Throughout the world, many thousand species of mites have been identified and every year new kinds are found. Mites vary greatly in appearance and habits. They range in size from those 90 small that they cannot be seen without the aid of a microscope, up to some which are about one-half inch long. Some of the tiniest are wormlike and suck the juices of plants, causing blemishes and galls. Other pigmies live in the breathing passages of bees.
Mites vary in color from white and pale yellow, gray or green to brilliant red or orange.
A few species bear their young alive but, generally, the female lays from two dozen to a hundred or more eggs. From the egg is hatched a nymph much smaller than the adult but similar in appearance except that, in most species, it has only six legs. From the last molt emerge an eight-legged fully equipped adult. Some are parasites that live on the outside of animals' bodies but some burrow into the body. Species such as the soil mites, and those that prey on weevils or other injurious insects, are beneficial.