Acarus, the name of a genus of insects, commonly called mites. They belong to the spider family. They are all extremely minute, and mostly microscopic insects. Some are parasitic, as the itch insect, acarus scabiei. The different species infest brown sugars, meal, cheese, etc. To collections of insects and stuffed birds they do much injury. Camphor tends to keep them off, and corrosive sublimate is a still more effectual protection. (See Epizoa, and Itch.)