Any plant-feeding mite in the family Tetranychidae, common pests on houseplants and agriculturally important plants. Adult spider mites are tiny, about 0.02 in. (0.5 mm) long, and often red. They spin a loose silk webbing on infested plants. A heavy infestation can cause complete defoliation. Because of their increasing resistance to pesticides, they are difficult to control. One effective control is the use of another, predatory, mite species.