About blister beetles
There are 250 species of blister beetles in the United States. The name blister refers to the chemical cantharidin in their bodies. This chemical will blister the skin if the beetle is crushed against it. The adult beetles are 1/2 to 3/4 inch long, slender and the elytra or wing covers are soft and flexible. The color may be black or gray, brown or yellow and sometimes striped or margined. They feed on flowers and foliage of a wide variety of plants including aster, calendula, Japanese anemone, chrysanthemum, gladiolus, dahlia, dianthus, delphinium, phlox, and zinnia. Blister beetles are unusual in their life history. The larvae are predaceous (they feed on eggs of grasshoppers), but the adults are plant feeders.
Margined blister beetle. Photo: Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org
Handpick the beetles to control small numbers. Wear gloves to protect the skin.