Order of the class Arachnida that includes ticks and mites. Acarina is the largest arachnid order and contains about 10,000 species. They are of major economic importance and nuisance value; many species are parasitic on man or domestic animals, and others consume food crops.

Members of the Acarina order vary in habit and structure, but the body is usually globular and presents no exact division between the abdomen and cephalothorax. The organs are simple, and the mouth is adapted for biting or sucking. Sarcoptes scabiei causes mange, and Tyroglyphus siro is the cheese mite.