These beetles are notorious for quickly stripping vegetables (especially tomatoes) and ornamentals of their foliage. There are several species of blister beetles which vary in size (often between 0.5-0.75 inch long) and color (such as black, gray or brown-striped), but most are recognized by their elongated, narrow, cylindrical, soft bodies with middle body part (thorax) narrower than the head or wingcovers.
Some home gardeners like to use hand picking as a nonchemical method for controlling these large insects. However, wear gloves and use caution because these beetles contain a substance called cantharidin. This chemical is an irritant capable of blistering internal and external body tissues exposed to the chemical. On tender human skin, body fluids of adult blister beetles may cause large, erect, watery blisters.
Chemical control of blister beetles is also possible and may be the only practical method of control if populations are large. Cyfluthrin (Bayer Vegetable and Garden Insect Spray) and permethrin (Bonide Eight and Hi-Yield Lawn, Garden, Pet and Livestock Insect Control) are recommended. Cyfluthrin and permethrin have a 0 day waiting period on tomatoes.
K-State Research Extension