Blister Beetle Risk To The Area

Blister beetles are here once again, and it is a good idea to scout for them in your fields, particularly alfalfa, prior to cutting. Blister beetle larvae feed on grasshopper eggs, which is why we’ve seen such large populations the last few years. Adult blister beetles contain a cantharidin toxin in their body fluids which is released when the beetle is crushed. This can blister people’s skin and can also be deadly to livestock and horses. There are a few species of blister beetles that are common in this area: ash-gray, black, and gray with spots. These species are less toxic than the black and orange striped beetle that has not yet been reported in Montana. Blister beetles can be found on many crops besides alfalfa, including canola, soybeans, dry beans, sweet clover, and some weed species. Feeding damage is typically not economically damaging in field crops. There are several management options for forage crops to reduce the risk of livestock poisonings.

Blister beetles are attracted to the blooms on the alfalfa, so harvesting at 10% bloom or less will reduce the potential for infested hay. Additionally, blister beetles are gregarious and often feed for a short period and then disperse. If you find large populations in your field, delaying harvest for a few days until they move out will be beneficial. Unfortunately, insecticides are not the best option for blister beetle management as even when dead, the beetles are still toxic and can still end up in the hay. Lethal doses of the black and gray blister beetles are up to 200 to kill an adult horse, and as low as 30-50 of the striped beetles to kill an adult horse. Contact the Richland County Extension office with any questions regarding blister beetle, 406-433-1206.