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Blister beetles follow grasshoppers’ upward trend

by Wyoming Livestock Roundup

Riverton — Wyoming hay producers are being cautioned to check their fields for blister beetles and adopt management practices to minimize the number of insects present in hay harvests.
    Following a report of blister beetles early August, Wyoming State Veterinarian Jim Logan says specimens of the insects were taken to the Fremont County Weed and Pest and the University of Wyoming for verification. The individual who reported the insects slapped one on his neck and the area blistered before he returned to the house.
    While Logan says it’s the first time he’s dealt with the insect in his capacity as a practitioner, he has seen horses die after consuming the insect. In his experience he says he hasn’t seen cattle or sheep affected by the insect, but knows of fellow practitioners who’ve witnessed such losses.
    University of Wyoming Extension Entomologist Scott Schell says the insects have also been confirmed in the Sheridan area. A native species, the insect’s populations vary and may be high as a result of Wyoming’s higher than usual grasshopper population.
    As Schell explains of the Epicauta pennsylvania species of the beetle confirmed in the Sheridan area, adult beetles lay their eggs on the ground. The first instar of the young insect is quite mobile and finds a grasshopper egg pod to feed on over the winter months. Adults emerge the following year as early as June and as late as September.
    “Adults feed on flowers,” says Schell. “They’ll also swarm on flowers for mating so you’ll often see two beetles coupled together on the flowers. Some of the worst places for them are those corners that didn’t get cut and the alfalfa goes into full bloom, or a little missed edge.”
    “When you swath hay,” says Schell, “the conditioner is designed to crush the stem. It can also crush beetles into the windrow.  The beetles are baled right into the hay and that’s how livestock get poisoned by it. In the old days when people cut hay with a sickle blade, beetles wouldn’t be killed and they’d fly off before the hay was put up.”
    Schell says, “In some areas where they are a big problem, and they supply the horse hay market, ranchers will do things like take their hay conditioners off.”
    On the bright side Schell says, “According to the research it takes a lot of blister beetles to kill a horse. The black blister beetle most commonly found in Wyoming rarely swarms in such numerous masses.” A table within this article details the toxicity levels of the different species.
    With that said, risk of poisoning as a result of the insects is a serious issue. “When a horse gets blister beetle poisoning,” says Logan, “the symptoms are rapid and extreme.” Logan says, “Depending on the species of the beetle, the amount required to sicken or kill a horse can be a very small amount.”
    Schell says, “ Blistering in the horse’s mouth and blood in the urine are diagnostic symptoms of blister beetle poisoning.  All hay should be inspected for foreign objects, dead animals, or mold before being fed to your horse.”
     He further adds, “Certified hay is only certified to be free of noxious weeds not blister beetles.  Buying hay from a cutting of alfalfa made when it is not in bloom is a good approach to minimize risk to your horses.”
    For those looking to purchase horse hay Schell advises, “They need to talk to the supplier or the farmer or rancher producing the hay. Make sure they are aware of the dangers of blister beetles. Ask what precautions they take and if they harvest their hay before the alfalfa is in full bloom.” He says the beetles tend to be less of an issue in those areas, like Torrington, where growers aim for high protien alfalfa that’s most often cut before full bloom. In areas less conducive to alfalfa production, where a grower may be seeking tonnage the alfalfa may be cut in full bloom, when the insects are of greater concern.
    Control isn’t really a feasible option according to Schell. “They are a native species and they do a service in that they help us suppress grasshopper populations.” He says the best approach is management to reduce risk. Looking toward 2010, given the current abundance of grasshoppers, Schell anticipates a higher population of the beetles.
    Additional information on the beetles can be found online at and at Jennifer Womack is managing editor of the Wyoming Livestock Roundup. Send comments on this article to

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