Dictionary.net

• [O.E.] Spanishfly, Cantharis veslcatoria [Gr.]. A beetle, about one inch long, green, with gold reflexions; rare in England. Ord. Coleoptera.

1895 - Glossary of terms and phrases
By Henry Percy Smith

• n. The Spanish fly, used in raising a blister.

1871 - The Cabinet Dictionary of the English Language