: any of various beetles (as the Spanish fly) that are used medicinally dried and powdered to raise blisters on the skin; broadly: any of numerous soft-bodied beetles (family Meloidae)
Blister beetle (Lytta magister).—Photo Research International
Any of approximately 2,000 species of beetles (family Meloidae) that secrete an irritating substance, cantharidin, which is used medically as a topical skin irritant to remove warts. In the past, cantharidin was often used to induce blisters, a common remedy for many ailments, and the dried remains of Spanish fly (Lytta vesicatoria) were a major ingredient in so-called love potions. Adult blister beetles, which are often brightly coloured, range between 0.1 and 0.8 in. (3–20 mm) in length. Blister beetles are both helpful and harmful to humans; the larvae eat grasshopper eggs, but the adults destroy crops.