CANTHARIDES , noun Spanish flies; a species of Meloe. This fly is nine or ten lines in length, of a shining green color, mixed with azure, and has a nauseous smell. It feeds upon the leaves of trees and shrubs, preferring the ash. These flies, when bruised, are universally used as a vesicatory, or blistering plaster. The largest come from Italy, but the best from Spain.

A beetle (Lytta, / Cantharis, vesicatoria), havin1g an elongated cylindrical body of a brilliant green color, and a nauseous odor; the blister fly or blister beetle, of the apothecary; -- also called Spanish fly. Many other species of Lytta, used for the same purpose, take the same name. See Blister beetle, under Blister. The plural form in usually applied to the dried insects used in medicine.