Many substances have been wrongly reputed to stimulate sexual desire over the centuries, although in most cases the alleged aphrodisiacs have failed to gain any lasting notoriety. Of those that have become legendary the most notorious of all has been "Spanish Fly", an alleged aphrodisiac powder or potion featuring in so many stories and rumours that it deserves special mention.

Spanish Fly is not really a fly at all. It's actually a beetle, Lytta vesicatoria (from Greek lytta=rage and Latin vesica=blister) of the order Coleoptera and the family Meloidae and is commonly known as the blister beetle. It is sometimes referred to as Cantharis vesicatoria, but the genus Cantharis is in an unrelated family, Cantharidae. The beetle is 15-22 mm long and 5-8 mm wide and is found on plants from the Caprifoliaceae (honeysuckle) and Oleaceae (olive) families.

Not only is Spanish Fly not a fly, it is not strictly Spanish either. It is certainly found in Spain, but also in other countries in the Mediterranean region and even in Russia. The reason it's known as the blister beetle is that when it feels threatened it secrets a caustic substance from its leg joints which in contact with humans causes irritation to the skin and can easily produce blisters. This colourless, odourless, crystalline substance is called cantharidin or cantharides and was first isolated in 1810 by a French chemist, Roviquet. It is this cantharidin that has been reputed to be an aphrodisiac rather than the beetle itself, although the traditional way of obtaining the cantharidin is not to collect or extract it in any way, but simply to gather beetles and to dry and crush them into a powder which will therefore contain cantharidin.

When this beetle powder is ingested the cantharidin is excreted by the body in urine, but during urination it causes irritation to the urogenital tract which subsequently leads to itching and swelling of the genitals. In antiquity this swelling was mistaken for sexual arousal and gave rise to the belief that the powder had aphrodisiac qualities. In reality the swelling of the genitals is a result of serious inflammation and can be very painful, not pleasurable, and unfortunately the kidneys will suffer inflammation as well and may be permanently damaged. Cantharidin is also highly toxic and its presence in the body can result in severe gastrointestinal disturbances, sometimes leading to convulsions and even a coma. In the event of a coma the outcome will usually be death within 24 hours.

The poisonous nature of cantharidin was demonstrated very well by the infamous Marquis de Sade in June 1772. Having sent his valet Latour to find prostitutes for his evening's entertainment, de Sade proceeded to offer them aniseed (saunf) sweets copiously laced with Spanish Fly, believing that this would "set them on fire". It didn't. Instead two prostitutes became wracked with abdominal pain and started to vomit incessantly. Three other women were spared this ordeal because they had secretly dropped the sweets on the floor after suspecting something was wrong with them.

A complaint of poisoning was lodged against de Sade with the Marseille authorities. The investigating officer, Chomel, found the two affected women in acute agony and was informed by the examining doctors that they had almost lost their lives. He ordered that de Sade and Latour be arrested, but de Sade had already realised he was in serious trouble and had fled to Italy. The case was brought to trial anyway and both men were found guilty of poisoning and sentenced to death. As the sentence could not be carried out they were hanged in effigy instead.

Another good example of Spanish Fly's lethal toxicity occurred in London in 1954. Arthur Ford had become infatuated with an office colleague, Betty Grant, but his advances to her had always been spurned. Desperate for her attention, and having heard wild stories about Spanish Fly when he was serving in the army during the second world war, he offered her some coconut bon bons which during his lunch hour he had laced with cantharidin powder. Another worker in the office, June Matlins, helped herself. The poison took effect on the women within an hour and they began vomiting blood and eventually collapsed in hideous pain. Next day they were both dead. Ford had eaten one of the bon bons himself, but one proved insufficient to cause any serious harm and he survived the experience, but only to face an investigation by Scotland Yard. He was later convicted of the manslaughter of the two women and was sent to prison.

Since Spanish Fly is sufficiently dangerous to even cause death, it may seem strange that this mythological powder or potion is still so widely sold. Don't be fooled. Shops offering Spanish Fly are almost certainly not reckless enough to be selling real Spanish Fly, even when they describe it as "real Spanish Fly" as they often do. Thankfully they are usually selling herbal products of one kind or another, which means that they aren't going to poison anyone and might even be selling something genuinely beneficial. However, products labelled or described as "Spanish Fly" frequently contain nothing more than pepper or some other spice, as these kind of ingredients can at least make someone feel hot if nothing else.

Other resources:

An article from Feminista, the online journal of feminist construction based in San Francisco - Not So Fly: The Myth Of Spanish Fly And The Problem Of Callous Attitudes Towards Rape by Yvonne Rasor.

An article from Science Reporter, a monthly magazine published in New Delhi by the National Institute of Science Communication - The Poison Sleuths: The Myth Of The Spanish Fly by Dr. Anil Aggrawal.