These beetles get their name because they contain a chemical that can raise blisters on the skin. Various species can be found throughout North America.
Blister Beetle larvae are beneficial in that they are predators of grasshoppers. The adults can be a problem because they feed on tomato, potato, beans. cabbage. corn and other crops. In small numbers they are usually tolerated because the larvae are beneficial, however occasionally large numbers emerge at one time and quickly strip foliage from plants.
You can also protect the plants with row covers.
These can be controlled by knocking them into a bucket of soapy water with a stick (don't touch them).
Image: Jon Yuschock, Bugwood.org