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.