Typically, we don’t see a lot of issues with blister beetle feeding in gardens. However, when they show up, blister beetles can rapidly defoliate plants. We have received reports of blister beetles feeding on pepper plants, radishes and green beans. In addition to garden produce, blister beetles will also feed on weeds within a garden, and they are often attracted to flowering plants.
There are several species of blister beetles that might be found in the garden. They all have a velvety appearance, and their thorax is narrower than their head and abdomen. Blister beetle coloration and size varies by species. The forewings of blister beetles do not fully cover their abdomen (i.e., their abdomen sticks out past the wings). A common blister beetle that can be observed within a garden is the striped blister beetle (Figure 1).
Blister beetles contain a chemical called cantharidin that is capable of producing painful blisters on human skin. Cantharidin is present in blister beetle hemolymph (blood) but can be exuded through reflexive bleeding when pressure is applied to the beetle. If you even brush a blister beetle against your skin while tending your garden, you may develop blisters.
In gardens, it may be possible to remove blister beetle infestations by hand. However, gloves should be worn as blister beetles contain cantharidin and picking them up may cause the chemical to be released. Ideally, one should use disposable gloves and be cautious not touch the gloves to unprotected skin. For severe infestations, insecticidal garden powder or spray may be used to reduce defoliation caused by blister beetles.
Blister beetle populations are often highest in areas where grasshoppers were dense during the previous year. Larvae of blister beetles consume grasshopper eggs, so managing grasshopper populations can be a preventative measure to reduce blister beetle populations in the future.