The South Dakota State University Extension Service reports that blister beetles have been found in alfalfa fields in the western part of the state. The bugs are particularly interesting in that they do both good and harm. The good: blister beetle larvae feed on the eggs of grasshoppers, a serious pest. The bad: blister beetle adults feed on alfalfa blossoms and also have a strong toxicity toward horses and livestock.
The SDSU Extension Service says producers need to actively scout their fields for these insects. Once the insects are found, producers have two options:
1: Early cutting: Swathing hay and allowing it to dry out before bailing will force any blister beetles to relocate elsewhere and reduce the risk to livestock. It is important that producers do NOT crimp the alfalfa. The toxicant, cantharidin, is oil based and can persist in the hay for years if the beetle is crushed while haying.
The ash grey blister beetle, the one species found in the state so far, is about a half-inch long, narrow bodied, with a gray body color and a very small thorax or neck compared to the head and abdomen, according to the SDSU Extension Service.