While Black Blister Beetles are more a problem in fields of alfalfa, they may come into your yard and attack flowers or vegetables. . They can be all black or in some cases they can be orangish-yellow with three black stripes on each of the wing covers. Most species of blister beetles have one generation per year. The larvae also attack plant roots. They lay their eggs in the soil at the base of the plants, where the newly hatched grubs eat their roots. Their bodies contain a toxin (cantharadin) that can cause blisters to form on the skin. So you don’t want to be handling these critters without gloves on.