blister beetle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various beetles of the family Meloidae, such as the Spanish fly, that secrete cantharidin, a substance that blisters the skin and is toxic to livestock that consume hay contaminated with the beetles.

from The Century Dictionary.

• noun A popular name of beetles of the family Meloidæ, derived from the peculiar poison (cantharidin) which is contained in their tissues.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun beetle that produces a secretion that blisters the skin