Cantharidin is sometimes referred to as Spanish fly because of its derivation from adults of the large meloid Lytta vesicatoria that is commonly found in Spain; it is a potent vesicant with a putative function as an aphrodisiac.

Meloids are herbivorous as adults, and their larvae are parasites of bees or eat grasshopper eggs.

Cantharidin is also a potent blistering agent.[…]Individual meloids may contain as much as 17 milligrams of cantharidin, or 10% of live weight.

2009, "Coleoptera", entry in Vincent H. Resh, Ring T. Cardé (editors), Encyclopedia of Insects, page 198,
Although meloids are known to produce cantharidin, transfer of this compound during meloid mating has not been documented.

Meloid

Meaning

Noun