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. Last Updated: 07/27/2016

Desert Beetle Lives by Bee Sexploitation

Sex may be powerful, but the exploitation of sex seems more powerful still.

Take, for example, the blister beetle, a tiny creature that just happens to be the source of the fabled aphrodisiac Spanish fly. The blister beetle must find some way to enter a bee's nest if it wants to raise a family of its own. According to a new study, success depends on a bunch of beetles getting together, clumping into a bee-like ball and seeming sexy enough to lure a prowling male bee into a mating attempt.

Not only does the male bee get a rude awakening, but the clump of beetles gloms onto the bee's front side, and stays there until the hapless male finds a real female, and then mates.

As the bees join, the beetles bail out, moving from the male's belly to the female's back, thus hitching a free ride directly into the female's nest. The bees involved are so-called solitary bees that live in single nests, not the beehive type.

Once inside the nest, the blister beetles drop off, transform into a worm-like stage and do real damage. The worm kills the bee's egg and consumes the carefully stored supply of pollen and nectar. Not a welcome guest, certainly.

"Eventually they pupate and hold over until winter," said entomologist John Hafernik, "and then emerge as wingless beetles."

After leaving the nest, the beetles feed on plants called loco weed and then mate. Each female beetle then produces thousands of eggs that get buried in the desert sand. On hatching, "they come out all at once, crawl up on the plant stems, coordinate their behavior and form into these aggregates that mimic the female bees," Hafernik said.

This strange behavioral phenomenon was spotted in the early 1990s while Hafernik was leading his San Francisco State University students on a field trip.

"I got started on this sort of by serendipity, on a field trip to the Kelso Dunes" area in California's Mojave Desert, he said. "What got me started was capturing a bee with all these larvae on it. I knew this wasn't what my professors told me should be going on here. The bees weren't reading the textbooks."

In 1999, on sabbatical, Hafernik and a coworker, Leslie Saul-Gershenz, returned for a longer-term study of the bee-to-beetle relationship at Kelso Dunes. They soon concluded that the beetles were exploiting sexual mimicry for their own advantage.

Although this behavior was unknown, reported for the first time this week in the British journal Nature, the blister beetles themselves are familiar. They are so named because many produce a fluid called catharidin, which "if you put it on your skin, causes a blister. For some people it can be painful," Hafernik said.

Under natural circumstances, the blister fluid is a defensive weapon because it tastes awful for predators, causing internal irritation if swallowed. And there is another sexual angle: "On the street," Hafernik said, cantharidin is known as Spanish fly, supposedly a powerful sexual stimulant - but which is known to be quite painful, even dangerous, if taken internally.