Terrifying Fungus Hijacks Sex Orgies Among Cicadas and Then Destroys Them

A pair of Illinois cicadas seen in 2007. Scott Olson/Getty Images

Every 13 or 17 years, cicadas crawl out from the ground in unison for a wild mating orgy that ensures the production of the next generation. But all that sex is a great opportunity for something else—a fungus that puts a gruesome spin on cicada romance.

"It's a fun story for us, not for the cicadas," John Cooley, a biologist at the University of Connecticut, said in a press release. He's the first author of a new paper on the infection, published in the journal Scientific Reports.

The fungus itself isn't new: scientists have been watching it for more than a century. But Cooley and his colleagues wanted to take a closer look at precisely how the fungus was changing cicada behavior.

Those behavioral changes affect a habit called wing-flicking, which is how female cicadas signal their interest in a male. The flicks, which produce noise, are synchronized with the male's vocalizing and tell him he can approach to proceed to the next stage of mating.

But a fluke observation in 1996 of a male cicada infected by the fungus confused Cooley. That male flicked its wings like a female, convincing another male to try to mate with it. The new study builds on that observation by playing audio recordings of male calls to infected cicadas and seeing how they responded.

The team found that cicada behavior varied, depending on how the insect had been infected in the first place. Cicadas pick up "Stage I" infections while they are climbing out of the soil as the insect equivalent of teenagers.

The infection changes the male's mating behavior. After the fungus-laden cicadas emerge from the soil, they masquerade as eager females, attracting other males into trying to mate with them. The males who fall for the trick become infected themselves and spread the fungus to healthy females they then try to mate with.

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The insects that catch the fungus from their mates have what is called a "stage II" infection. That name doesn't mean that phase is worse than stage I. The study found that insects who become infected this way stick to their usual mating behavior.

But whichever way the cicadas catch the infection, it's bad news. The fungus hijacks the insect's abdomen as a factory for creating spores—eventually causing the abdomen to fall off entirely.

To really seal the deal for the fungus, the cicadas' sex drive isn't dampened in the least by the infection. Even losing a huge portion of their bodies, including their genitalia, doesn't put a dent in the mating frenzy. And as the insects continue to try mate as much as possible, they spread the infection even further.