Submitted Photo Drought conditions this year are increasing the blister beetle threat to cattle and other livestock as well as humans. Photo from NDSU.

Paige Brummund, Ward County Extension Agent – Agriculture and Natural Resources, has found blister beetles in alfalfa fields in the local area.

Farmers and ranchers are being advised that the drought conditions this year have increased the number of blister beetles,which are toxic to livestock, especially horses, as well as humans.

In humans, the blister beetle can cause a local reaction or skin irritation if the beetles are crushed on the skin, Brummund said.

The irritation and blisters that form can be painful but usually are not life-threatening to humans, according to the National Capital Poison Center. For more information about human contact with blister beetles vist the center’s website at www.poison.org/articles/blister-beetles-do-not-touch-194.

The immature stage of blister beetles feeds on grasshopper eggs, said Jan Knodel, NDSU Extension entomologist. She said blister beetles produce a poison called cantharidin, which is toxic to people and livestock, especailly horses but cattle and sheep also can be poisoned. The cantharidin oil is released when the beetles are crushed and even dead beetles have high levels of the toxin.

According to NDSU information, the level of toxicity to livestock varies by blister beetles species. The species include black, spotted, three striped and ash-gray blister beetles. It is estimated 30 to 50 of the striped blister beetles could be potentially lethal to horses. Symptoms of toxicity in horses include sores on the tongue and in the mouth, depression, colic, sweating, diarrhea, blood in the feces and frequent urination. Cattle also may have sores in their mouth.

Anyone suspecting cantharidin poisoning in their livestock should contact their local veterinarian.

NDSU officials said after alfalfa is cut, the beetles often move into blooming canola and other blooming field crops.

Ways to reduce the threat of blister beetles include cutting alfalfa at less than 10% bloom and/or late in the season (mid-August to early September.

If the beetles are sprayed, Brummund said the dead beetles still are toxic.

For more information about blister beetles contact your local NDSU Extension office.

Here are some ways to reduce the threat of blister beetles:

– Control blooming weed hosts near or in alfalfa fields.

– Cut alfalfa at less than 10% bloom and/or late in the season (mid-August to early September).

– Check fields 24 hours prior to cutting to ensure that new swarms of blister beetles have not re-infested the fields.

– Allow cut hay to fully dry before raking to encourage the beetles to move out of the hay. Raking may dislodge dead beetles from hay; however, the potential still exists for cantharidin in the hay.

– Scout harvested hay and underneath windrows closely for blister beetles and allow blister beetles to move out of drying hay before baling. Turning the windrows may be helpful to get blister beetles to move out.

– Use equipment without hay conditioners or crimpers that may crush blister beetles because the crushed beetles can contaminate the hay.

– Source: NDSU Extension