Blister Beetles: They are back – with a vengeance!

CSU Extension Website

Last year I wrote an article about blister beetles, but with recent outbreaks reported, thought it would be a good refresher. Several different species of blister beetles, not only in rangeland, but in lawn and garden settings as well, have been reported and observed.

First instar blister beetle larva are predatory to grasshopper eggs (Kinney, 2010). Blister beetles usually only have one generation per year and grasshopper eggs that were laid last summer were the first to hatch this summer. Like most livestock, the more feed available the better the population survival – more grasshopper eggs, more feed for blister beetle larva, more blister beetles.

In sufficient quantities, cantharidin, the chemical produced by blister beetles, is toxic to humans and animals. Animal deaths are primarily associated with horses, but cattle and sheep are also susceptible. In a newsletter article Dr. Frank Peairs, CSU professor, states that there are over 100 species of blister beetles in Colorado.

Three are the most common; the black, the spotted, and the three-stripped. But, not all blister beetles are created equal. The Three-stripped is of most concern to Colorado livestock owners for two reasons: 1) populations tend to congregate in swarms; 2) they produce much higher concentration of cantharidin then other species.

Dr. John Capinera determined that the lethal dose for an 825 pound horse was 1700 Black blister beetles, 520 Spotted blister beetles, and only 120 Three-stripped blister beetles.

Hay producers are encouraged to check their hay fields for blister beetle infestations. Although populations may appear high in rangeland situations, further treatment may not be economically viable. Blister beetles seem to be attracted to blooming plants, so gardeners should be vigilant for infestations as well.

Colorado State University Extension has a fact sheet found at:, dealing with blister beetle life cycles and offers management tips.

From Bruce Fickenscher
CSU Extension
Eads, CO

Filed Under: AgriculturecommunityEconomyHealthPublic Safety


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