Black Blister Beetle
Colorado Insects of Interest
Black Blister Beetle
Scientific Name: Epicauta pensylvanica (DeGeer)
Order: Coleoptera (Beetles)
Family: Meloidae (Blister beetles)
Distribution in Colorado: Statewide and common.
Adults of the black blister beetle are almost always found on flowers and appear to restrict their feeding to pollen and nectar. They may be found on a wide variety of plants but most often are seen on yellow-flowered plants, notably goldenrod and rabbitbrush. Occasionally they may mass in crops during late summer but, unlike some other blister beetles, do not damage foliage and are usually concentrated on flowers of either the crop and/or flowering weeds. Black blister beetles may be present well into October, as long as suitable flowers are available and killing frosts have not occurred.
Blister beetles (Meloidae family) get their common name from the production in their blood of a highly toxic compound, cantharidin, which is irritating and even capable of producing blisters in high enough concentration. However, the black blister beetle is a species that produces very low levels cantharidin.
Related Species: The black blister beetle is one of about 35 species of blister beetles in the genus Epicauta that occur in Colorado. All are thought to similarly develop as predators of grasshopper eggs but most, unlike the black blister beetle, feed on leaves and flowers of plants, particularly legumes. A common pollen feeding species that also is found on flowers in late summer is Epicauta ferruginea Say, which is variably colored from pale rusty red to grayish-brown. Epicauta aspersa Werner is another gray blister beetle that may be present at flowers in mixed populations with the black blister beetle in later summer and early fall.
Blister beetles have some notoriety in the state because of the potential for them to hurt livestock, particularly horses, when accidentally baled into hay and fed. The most important species in this regard is the threestriped blister beetle, Epicauta occidentalis Werner (formerly E. lemniscata). It has very high levels of cantharidin in its blood and periodically masses in blooming alfalfa fields. The three-striped blister beetle is a species that is present early in the season, sometimes massing and contaminating the first cutting of alfalfa.
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