The other beetles cause blisters on human skin if they are squashed. The body fluids contain alkaloids that are part of their self-defense.
The beetles are elusive, which helps them stay out of the way of grazing livestock. Infested alfalfa fields can have hundreds of thousands of the beetles. Most of the 20 species are elongated, with striped wings, most often orange in color. Some are gray and darker gray.
When disturbed, the beetles drop to the ground and seek cover.
"They are very alert," Bailey says. He recalls the first time he saw blister beetles en masse was at alfalfa plots at the MU Thompson Farm near Trenton, Mo.
"There must have been a hundred thousand of them," Bailey recalls. "They all turned and looked at me at once. Then they dropped out of sight. They were gone. I couldn't see a one."
Horses and pasture-raised chickens are most at risk. Cattle, goats and sheep don't seem to be bothered.
The danger comes from crushing and baling the beetles with hay. "When we used to cut hay with a sickle-bar mower, the blister beetles could get out of the way," Bailey says. "With haybines, they are crushed when the beetles go through the rollers."
Horses should be fed only from first-cutting alfalfa. Mostly, blister beetles don't arrive until the second or third cutting of hay. Alkaloids in the blistering agent can cause the lining of the horse's digestive tract to slough off. That is fatal to horses.
University of Missouri Extension regional agronomists have recommendations on scouting and controlling insect pests.
For more help on what to look for when scouting fields check out the accompanying MU video.
Source: University of Missouri Extension