Though blister beetles make an appearance each year, the bug species is making itself more well known this summer due to the excessive dryness and heat.

“It is primarily because of the drought that we are seeing some high numbers of blister beetles in the region,” said Jane Knodel, North Dakota State University Extension entomologist and professor.

The rising number of blister beetles is in direct correlation with the growing number of grasshoppers many areas are experiencing this summer. According to Kevin Wanner, a Montana State University associate professor and extension entomologist, young blister beetles feed on grasshopper eggs. With a heavier grasshopper population, more eggs are laid. Therefore, there are more grasshopper eggs for the blister beetles to feed on.

While blister beetles do minimal damage to plants, the main concern surrounding the beetle species is their toxicity to livestock, especially horses. It is still unknown how toxic the blister beetles are to beef cattle. However, cattle producers should still keep an eye out for the beetle species.

“Blister beetles contain a chemical toxin (cantharidin) that is poisonous to horses. There are several species of blister beetles, with some being more toxic than others,” said Dr. Carolyn Hammer, a North Dakota State University professor and program director for the equine sciences department.

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The blister beetles travel in swarms and prefer to congregate in blooming alfalfa fields, a problem for equine owners and producers. When the alfalfa fields are cut, the beetles are left in the hay crushed or killed. The toxin does nor decrease over time, and does not leave the beetle’s body even though the insect is now dead. According to Knodel, about 30 to 50 of blister beetles is enough to be lethal to horses.

“Cantharidin oil is released when beetles are crushed, and even dead beetles have high levels of the toxin,” Knodel said.

If at all possible, the best way for equine owners and producers to avoid their animals ingesting blister beetles is by not feeding alfalfa, according to Hammer. Of course, that cannot always be avoided.

To help cut back on the blister beetle population in their fields it is recommended that producers control blocking weed hosts in their alfalfa fields, cut their hay crop at less than 10% bloom and check their fields 24 hours prior to cutting their hay to make sure that a new swarm of beetles have not entered their fields, are a few of the steps producers can take.

Unfortunately, there is no cure for ingesting blister beetles, only supportive care.

“After ingestion by the horse, the tissues affected are usually the GI tract, but also the kidney, bladder and heart. Early clinical signs that an owner might observe tend to be very non-specific and include colic, increased heart rate and respiration rate, decreased appetite and depression, drooling, diarrhea and bloody urine. Depending on the amount ingested, death can occur,” Hammer said.