This is a green 11-21mm long European beetle with an unpleasant smell. It feeds on tree leaves; the larvae grow in the wasps’ nests. When the Spanish fly feels in danger, it secrets a kind of buttery liquid which causes reddening and rush on the skin. After long researches, it was established that the poisoning effect is due to a colorless, odorless crystalline substance which was called cantharidin, after the French chemist who first extracted it. The lethal dose for a human is about 0.03g. High doses of cantharidin cause excessive salivation, stomach, kidneys and urino-genital system inflammations as well as headache, vomiting and bloody diarrhea. The affected person can develop even seizures but a lethal end is not very common. 

This substance was very often mentioned in the old books of pharmacology. People used cantharidin tincture to stimulate the growing of the hair and to heal rheumatism, pneumonia, swellings and gout. Another interesting application of the substance was as an ingredient of “love drinks”. It really increases the sexual attraction but the chasing of extreme effects often led to severe poisonings. There is a true story which can illustrate this best:
Once, marquise de Sad (that’s where sadism comes from) decided to make a joke with his guests. To stimulate their sexuality, he gave them Spanish fly-eaten sweets. His idea resulted in a mass poisoning with many death cases. Sad was sent to prison for life.