Blister Beetle

Insects of America

The blister beetle – named for its ability to exude from its joints a liquid that causes painful blisters on your skin – ranks close to the top of the list as the insect world’s most clever and odious imposters, even if it is often colorful and relatively innocent looking. 

Blister beetle

According to Donald J. Borror and Richard E. White, A Field Guide to the Insects of America North of Mexico, the typical blister beetle has an elongated and pliable body.  It measures about a half inch to an inch and a half in length.  The beetle, says New Mexico State University entomologist, Charles R. Ward, “Blister Beetles in Alfalfa,” has thread-like antenna, non-bulging compound eyes, a bowed head, and relatively long legs.  “Primary body colors,” said Ward, “include black, brown, or gray; different species have spots or stripes of yellow red, brown orange, black, or white,” depending on the species.

Of the more than 300 species that occur in the United States, several dozen make their home in the Southwest, where the adults feed, sometimes voraciously, on both wild and cultivated plants, often favoring mesquites.  One of the Insects of the Southwest authors said, “I have seen stripped [by blister beetles] trees in a straight line several hundred feet long.”  If inadvertently harvested and bailed in large numbers with alfalfa, the blister beetle, which contains a toxic chemical compound called “cantharidin,” can poison domestic animals, especially horses, that eat the hay. 

In some species, the blister beetle larvae prey on the eggs of grasshoppers, actually imposing some control on a historic pest.  In other species, newborn larvae, called “triungulins,” pack themselves together by the hundreds in a single mass that mimics – and even smells like! – a female solitary bee, according to a year 2000 San Francisco State University news release, “‘Spanish Fly’ Beetles Use Sex and Subterfuge to Infiltrate Bee’s Nests.”  Collectively, with the precision of a military band, they march to the tip of their host plant stem, where they pose provocatively as a single female bee, displaying a phony sexuality, luring lusty male bees.  They quickly attach themselves to a foolish male when he tries to mate with them.  They transfer to various females when the male tries to couple with more rewarding mates.  They cling to the unwitting females for a free ride to the bees’ nests.  “Then,” said DuPuy, “showing no gratitude for the transportation furnished, this vicious little creature alights, crowds it way into a cell which the bee has arranged for its young, eats her larva there and feasts for growing days on the food that has been provided for that larva.”

by Jay Sharp

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