Scout for Blister Beetles

Reports of large swarms of blister beetles on grass pastures and home gardens came out of Howell, Taney, and Barry counties in Missouri this week.

The most common type of blister beetle is the striped blister beetle which is a small, narrow bodied, brown to orange beetle with black stripes. These beetles contain a blistering substance called Cantharidin which causes blisters and tissue damage.

Generally, blister beetles become a problem to livestock when crushed during the alfalfa baling process. These beetles can end up in alfalfa hay and fed to livestock, causing illness or death. With the dry or droughty conditions in some areas of Missouri, blister beetles are seeming to swarm onto pastures, barn lots, and in gardens to feed on pollen and nectar.

All livestock may be affected by consuming blister beetles but horses are especially sensitive to cantharidin. The tissues most affected by the Cantharidin are tissues of the gastrointestinal and urinary tracts as well as the heart.

Because of this, symptoms of blister beetle poisoning are varied and usually worsen quickly. Some symptoms include colic or gastritis, mouth sores, salivation, dunking mouth into a water source, not eating, watery or bloody manure, stretching to urinate, frequent attempts to urinate, and bloody urine.

Damage to the kidneys, intestinal tract, and heart can ultimately lead to death of the livestock. While content of cantharidin varies in individual blister beetles, consumption of approximately 30-50 beetles is generally considered lethal to horses but the lethal threshold has not been well identified in cattle or sheep.

Livestock owners should be scouting for blister beetles. If blister beetles are found, they should try to move animals to barns or dry lots that blister beetles will generally avoid. The livestock should be fed in feeders up off the ground to try to avoid any consumption of blister beetles. 

Carbaryl or Sevin can be used to kill blister beetles at the following rates:

- Carbaryl at 0.5 to 1.0 pound active ingredient per acre

- Sevin XLR Plus at 1 pint to 1 quart

- Sevin 80S at 0.67 to 1.25 pounds

- Sevin 50W at 1 to 2 pounds active ingredient per acre

For more information, visit:

https://aaep.org/horsehealth/blister-beetle-poisoning

https://extension.missouri.edu/publications/g4569