They get their name from a caustic chemical they produce called cantharidin. When crushed, the beetle can literally bleed the chemical from its joints and skin contact with it can result in blisters.
Blister beetles are a soft bodied beetle that range in size from 1/2 to 1 inch in length. There are several species of blister beetle in the U.S. Adults range in color from an ash gray to bright yellow with black strips. They usually are seen during the day hanging out on flowers and also are attracted to lights at night.