"Spanish fly" is any number of powders, usually made of things like chili powder and insect parts, that irritate the vagina. It doesn't turn you on, it makes you burn and itch. Don't use it!
1) There is such a thing -- the extract of the beetle Lytta vesicatoria. 2) The active ingredient is cantharadin, an irritant/blistering agent. 3) It is correct that the supposed sexual stimulus is...