Blister Beetles in Hay Are Dangerous to Livestock

By: Karen Forseth, MSU Extension Teton County Agent

The whirlwind that was May and June has quickly moved into July. Gardens are growing and starting to produce. Haying is in full swing. Our thoughts are with the producers in the eastern side of our state. The drought and grasshoppers have really taken their toll on those areas. While those are bad enough, another potential issue is beginning to show up: Blister beetles.

Blister beetles are problematic due to a toxin they produce known as cantharidin. Even after the beetles are killed, the toxin still has the potential for damage. Therefore, forage that has been baled with blister beetles can pose a problem. Horses are especially sensitive but other livestock species such as cattle and sheep can also be affected. Livestock that consume blister beetles can suffer from blistering of the esophagus and stomach. Heart and kidney function can be impaired. In severe cases, death can occur.

There are multiple species of blister beetles that have varying levels of cantharidin. The three striped blister beetle, Epicauta lemniscata, contains especially high levels of cantharidin, which is toxic to horses. Certain species are known to swarm, increasing the risk for large consumption rates in hay. Montana, in general, has not seen the striped species of blister beetle nor those known to cluster in swarms. The least toxic is the black blister beetle, Epicauta pennsylvanica. A species that occurs in Montana.

Immature blister beetles feed on grasshopper egg pods or the larval cells of solitary bees. Last year’s large population of grasshoppers has likely contributed to the higher-than-normal populations of blister beetles in the state. Current populations of grasshoppers could potentially lead to high blister beetle populations next year, as well.

If you see the striped species: collect it in its entirety and bring it into the Extension Office for a positive identification. This will help monitor the population in Montana.

The following links have more information about the blister beetle:

MSU Extension MontGuide: Blister Beetles in Montana

Western Ag Network Article on blister beetles in hay

MSU Extension AgAlert: Blister Beetles in Alfalfa

Please contact the Teton County Extension office for more information. 406-466-2491 or email Karen at: karen.forseth1@montana.edu