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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Look but do not touch: Blister beetles, Epicauta pensylvanica and E. funebris


Black blister beetles are common visitors to goldenrod in late summer and early autumn.


Meadows are spectacular in August and September when members of the aster family put on their finest performances. Last month during the 6th anniversary celebration of the Robinson Nature Center in Columbia, MD, Bug of the Week had the good fortune to visit several magnificent pollinators taking advantage of Mother Nature’s bountiful blossoms. Goldenrod is one of the richest late-season sources of nectar and pollen for dozens of insects. Among the bees and butterflies a bevy of black blister beetles, Epicauta pensylvanica, cavorted on goldenrod. These insects are not to be taken lightly. If handled roughly or crushed against your skin, blister beetles release blood laced with potent irritants called cantharidins. Upon contacting skin these compounds can raise nasty looking blisters. See the photograph at the following web site if you are curious (scroll towards the bottom):

Larvae of Epicauta undergo a fascinating from of metamorphosis called hypermetamorphosis. After hatching from eggs, tiny larval blister beetles called triungulins get busy finding food. In some species, triungulins climb flowers, hop aboard a visiting bee, and hitch a ride. Back at the nest of the mother bee, the predatory vagabond jumps off and consumes the developing bee babies and the provisions left by their mothers. How rude! Larvae of other species of blister beetles scurry on the ground and locate nests of grasshopper eggs. Hungry triungulans burrow into the soil and the underground omelet becomes a banquet for the blister beetle larvae.


Potato leaves provide a tasty meal and apparently inspire amorous behavior in margined blister beetles. Will persistency payoff or will this choosy female thwart the advances of the hopeful suitor?   

When foraging on plants in meadows, Epicauta have been inadvertently baled in hay and fed to horses and other farm animals. Horses are especially sensitive to toxic cantharidins and consuming them can be lethal. In addition to posing threats to humans and livestock, Epicauta funebris, a.k.a. the margined blister beetle, is sometimes an important pest of eggplants, potatoes, tomatoes, and beets. If you see blister beetles on plants near your home or in the meadow in the waning days of autumn, resist the urge to handle or eat them unless you desire a blistering experience.


 Bug of the Week gives a shout out to the Robinson Nature Center for providing the inspiration for this episode. To learn more about blister beetles and their pest potential in hay, please visit the following websites: