Lytta vesicatoria or Spanish fly is an emerald-green beetle in the family Meloidae, with approximate dimensions of wide by long. The genus and species names derive from the Greek lytta for rage, and the vesica for blister. It is one of a number of species that are collectively called blister beetles; it and other such species were used in preparations offered by traditional apothecaries, often referred to as Spanish fly. L. vesicatoria is sometimes called Cantharis vesicatoria, although the genus Cantharis is in an unrelated family, Cantharidae.