I hadnt even heard of it but this was on the BBC website -
A warning about Spanish fly
Spanish fly, a substance made from the dried-out bodies of beetles, is reputed to be a powerful sexual aid. Taken as a powder, solution or tablet, it's understood to heat up the sexual organs and make you insatiable. On the contrary, Spanish fly is toxic and can actually be dangerous.
Spanish fly works by irritating the water passages in the bladder. Instead of a nice feeling of warmth, it can cause an extremely unpleasant pain and the inflammation can lead to long-term damage