Commonly found throughout southern Europe, parts of Central Asia and Siberia, the Spanish Fly (Lytta vesicatoria) is actually a beetle. They are signified by the secretion of Cantharidin, which is common among almost all male species of the blister beetle family (Meloidae).
The Spanish Fly, and some of its related species, were earlier used for the preparation of medicines by conventional apothecaries. Cantharidin, a toxic, defensive chemical found in the blister beetle, had been used for over a thousand years as a sexual stimulant. In concentrated amounts, the chemical causes severe blistering. It is potent enough to cause serious complications and is fatal above a certain dosage.