Cantharidin
Cantharidin is a poisonous chemical compound secreted by many species of blister beetle, and most notably by the Spanish fly, Lytta vesicatoria.
It was first isolated by Pierre Robiquet in 1810. It is an odorless and colorless solid at the room temperature. It is considered an aphrodisiac because male blister beetles give it to the females as a mating gift, but actually the female uses this poison to protect her eggs from predators. If cantharidin is ingested by human males, as it is excreted by the kidneys, it irritates the urinary tract causing spectacular swelling, called priapism, but this is quite painful and does not result in arousal.
Diluted it can be used to remove warts and tattoos. However, when ingested 10 mg is usually a fatal dose.