The Spanish fly is an emerald-green beetle in the family Meloidae, Lytta vesicatoria. It is 15 mm to 22 mm long and 5 mm to 8 mm wide, and lives on plants in the families Caprifoliaceae and Oleaceae. The beetle contains up to 5% cantharidin which irritates animal tissues. The crushed powder of Spanish fly is of yellowish brown to brown-olive color with iridescent reflections, of disagreeable scent and bitter flavor.
Spanish fly, or cantharides as it is sometimes called, is often given to farm animals to incite them to mate. The cantharides excreted in the urine irritate the urethral passages, causing inflammation in the genitals and subsequent priapism. For this reason, Spanish fly has been given to humans for purposes of seduction. It is dangerous since the amount required is minuscule and the difference between the effective dose and the harmful dose is quite narrow. Cantharides cause painful urination, fever, and sometimes bloody discharge. They can cause permanent damage to the kidneys and genitals.
Its medical use dates back to descriptions from Hippocrates. Plasters made from wings of these beetles have been used to raise blisters. In ancient China, cantharides beetles were mixed with human excrement, arsenic and wolfsbane to make the world's first recorded stink bomb. It is also one of the world’s most well-known aphrodisiacs. In Roman times, Livia, the scheming wife of Augustus Caesar, would slip it into food hoping to inspire her guests to some indiscretion with which she could later blackmail them. Henry IV (1050-1106) is known to have consumed Spanish fly at the risk of his health. In 1572, the famous French surgeon Ambroise Paré wrote an account of a man suffering from "the most frightful satyriasis" after having taken a potion composed of nettles and cantharides. In the 1670s, Spanish fly was mixed with dried moles and bat's blood for a love charm made by the black magician La Voisin. It was slipped into the food of Louis XIV to secure the king's lust for Madame de Montespan. In the 18th century cantharides became fashionable, known as pastilles Richelieu in France. Marquis de Sade is claimed to have given aniseed-flavored pastilles that were laced with Spanish fly to prostitutes at an orgy in 1772. He was sentenced to death for poisoning and sodomy, but later reprieved on appeal.
Also it was used as an abortifacient, stimulant (since one of its effects was producing insomnia and nervous agitation), and as a poison; in powder, mixed with the food, it could go unnoticed. Aqua toffana, or aquetta di Napoli, was one of the poisons associated with the Medicis. Thought to be a mixture of arsenic and cantharides, it was reportedly created by an Italian countess, Toffana. Four to six drops of this poison in water or wine was enough to deliver a painless death in a few hours.
In order to determine if a death had taken place by the effects of Spanish fly they had to resort to the vesicación test. One of those test methods consisted of rubbing part of the internal organs of the deceased, dissolved in oil, on the shaved skin of a rabbit; the absorption of the cantharides and its blistering effect are such that they became visible on the skin of the rabbit.
Cantharides are illegal in the United States, except for use in animal husbandry and by licensed physicians for the topical treatment of certain types of warts. Some internet or mail order suppliers of sex stimulants advertise such products like "Herbal Spanish fly", "Mexican Spanish Fly", or "Spanish Fly Potion". Most of these products are simply cayenne pepper in capsules, sometimes blended with the powder of ginseng, kelp, ginger or gotu kola. The products with the name "Spanische Fliege (Spanish fly)" that are available in Germany represent no danger with a normal application since they contain the active substance actually only in homeopathic dosage, diluted to be effectively non-existent.
Dawamesk, a spread or jam made in North Africa and containing hashish, almond paste, pistachio nuts, sugar, orange or tamarind peel, cloves and other various spices, occasionally included Spanish fly.
In Morocco and other parts of North Africa, a spice blend called Ras el hanout included cantharides in its list of ingredients at one time. However, the sale of Spanish fly in the Moroccan spice markets was banned in the 1990s.