ARI SHAPIRO, HOST:

Brood X cicadas are slowly making their way above ground in many parts of the country.

(SOUNDBITE OF CICADAS BUZZING)

SHAPIRO: And as if those large, brown bugs shedding their skins all over the place isn't creepy enough, some cicadas are taking it to a new level.

MATT KASSON: This is stranger than fiction, you know, to have something that's, you know, being manipulated by a fungus to be hypersexual and to have prolonged stamina and just mate like crazy.

MARY LOUISE KELLY, HOST:

That is Matt Kasson, associate professor of forest pathology and mycology at West Virginia University. Now, that fungus he's talking about - it's called Massospora, and it means cicadas lose more than just their skins.

SHAPIRO: Here's what happens. Just before the cicadas rise from the ground, the spores of this fungus start to infect the bug. Once the cicada is above ground, it sheds its skin, becomes an adult and its butt falls off.

KASSON: And a white plug of fungus starts to emerge. So it looks as if the backside of the cicada is being replaced either by chalk or by, like, one of those nubby middle school erasers that were all, like, known to, you know, use back in the day.

SHAPIRO: That white plug is full of spores. And as the infected cicadas fly around and try to mate, they are just spreading their spores from one partner to another.

KASSON: In that sense, it's sexually transmissible. It's a failed mating attempt, of course, because there's no genitalia back there.

KELLY: That is not all. Some versions of the fungus contain the same chemical as psychedelic mushrooms.

KASSON: It's giving them kind of a sense of prolonged wakefulness. These cicadas are like, I'm drugged and ready to go.

SHAPIRO: Ready to go and mate.

KASSON: Males that are infected will not only continue to try to mate with females, but they'll pretend to be females to get males to come to them so they can spread the fungus to even more individuals.

KELLY: Now, Kasson says a very small percentage of cicadas are infected with Massospora. And as far as he knows, the bugs - they have no idea what is happening.

KASSON: I don't imagine there's much pain - maybe a desire to listen to the Grateful Dead or something like that but no pain.

KELLY: So an alternative soundtrack there to keep in mind as you listen to the mating calls of cicadas outside your window this spring.

(SOUNDBITE OF SONG, "SHAKEDOWN STREET")

GRATEFUL DEAD: (Singing) You tell me this town ain't got no heart. Transcript provided by NPR, Copyright NPR.