Blister Beetles are affecting more than just alfalfa

By Colleen Buck

Montana State University Hill County Extension Agent

Blister beetles have been found in hay fields in Hill County.

Generally, these beetles inhabit alfalfa fields, however this year that is not the case. They have been found in grass hay fields as well as alfalfa fields.

Blister beetles get their name because they cause blisters when the cantharidin fluid found in their bodies comes into contact with skin or is ingested. They mainly affect horses fed hay containing blister beetles, however, they can be toxic to other livestock as well.

When the insects are consumed in hay containing blister beetles, livestock can suffer from blistering of the esophagus and stomach and kidney and heart function can be impaired; in severe cases, death can result.

There are multiple different species of blister beetles, each with their own concentrations of cantharidin. Some species are known to swarm like honeybees and have been attributed to many horse poisoning cases.

MSU Extension Entomologist Kevin Wanner said Montana generally doesn’t have the species that tend to aggregate or swarm. The blister beetle species that are found in Montana generally don’t have the toxin levels of other species in other parts of the country.

However, with this year being what it is, the more information people have the better.

South Dakota State University Extension reports that blister beetles prey on grasshopper eggs, so in areas where the grasshopper population is present, there will more than likely be blister beetles.

People should monitor their fields for black, grey, brown, striped or spotted type of beetles that are up to one inch long.

Other management considerations include using harvest equipment that allows the beetles to escape from mowed and swathed forage. Kansas State University has shown that self-propelled swathers without condition rollers but with windrowing attachments are safer than mower conditioners and sicklebar mowers. Raking hay before baling also allows the beetles to leave the windrows. Let hay dry down before baling, so that the beetles have a chance at getting out of the windrows. People who need help identifying the beetles can contact the Extension Office.

For more information, people can look up MontGuide MT200209AG, Blister Beetles of Montana or contact MSU Hill County Extension Office at 406-400-2333, email [email protected] or come find the office staff members at the Great Northern Fair this week.