Blister Beetles in the Pacific Northwest: Part 1

What You Need to Know about this Life Threatening Insect

by Alayne Blickle, Horses for Clean Water


Horse owners in many parts of the United States already deal with concerns of blister beetles in alfalfa hay as part of their everyday regimen. In the Pacific Northwest we have been relatively free of that worry—that is until now. Earlier this summer the Pacific Northwest & Treasure Valley Pest Alert, a newsletter distributed by the University of Idaho Extension and Oregon State University Extension, identified an outbreak of these poisonous insects in the foothills of Boise, Idaho. Todd Murray an entomologist with Washington State University in Skamania County, WA verified this and noted that the pests have also been turning up in Eastern Washington as well.

“Pacific Northwest native punctate blister beetle.” Photo credit Pacific Northwest Pest Alert

Specimens identified by Idaho State Department of Agriculture in the Boise Foothills are the native punctate blister beetle (Epicauta puncticollis.) Blister beetles are associated with grasshoppers and weedy conditions. According to the alert, the blister beetle larvae serve as predators of grasshopper eggs, but adult blister beetles feed on vegetation, occasionally moving to flowering field crops such as alfalfa. That is where the problem begins.

“Insects can easily be baled with hay. Here is a dried grasshopper found inside a bale of eastern Washington alfalfa/grass hay.” Photo credit Catherine Madera

Bodies of adult beetles contain the chemical cantharidin, a toxic chemical that protects them from predation by causing a painful blister when crushed. Cantharidin can be toxic, even lethal, to horses and livestock if ingested. Horses seem to be particularly sensitive to the toxins, especially when crushed beetle body parts are consumed in dried hay. According to Internet sources, cantharidin affects the gastrointestinal and urinary tracts of horses. Typical symptoms of cantharidin poisoning in horses include abnormal breathing patterns, submerging their mouth in water for long periods of time and restless behavior. Other symptoms are blistering of the mouth, colic, pawing, frequent attempts to urinate, jerking contractions of the diaphragm, diarrhea, discarded intestinal tract lining in the stool, and reduced levels of calcium and magnesium in the blood. Depending on the species of beetle, it is reported that ingesting someplace between several and 100 beetles will kill a horse. The toxin does not break down quickly and hay can remain infested for many years. Ruminants, however, seem to be more tolerant of the toxins.

Blister beetles have long (3/4 to 1-1/4 inch) narrow bodies, broad heads, and antennae that are about 1/3 the length of their entire bodies. The front wings are soft and flexible in contrast to the hard front wings of most beetles. The punctate blister beetle occurring in the Pacific Northwest is black, however other blister beetle species range in colors from tan to gray and even stripped.

Since fall is the time to buy your winter supply of hay, next month I will discuss some possible management considerations for buying hay.

Looking for a summer vacation, weekend getaway or horse motel for your travels? Visit Alayne Blickle this summer at her horse motel and B&B guest ranch, Sweet Pepper Ranch in Nampa, Idaho. www.SweetPepperRanch.com


Published September 2012 Issue

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