(NewsNation) — Trillions of cicadas will emerge and spread across several states in the U.S. this spring in an event dubbed “Cicada-geddon.”

And some of them will be hypersexual “zombie cicadas” infected with a sexually transmitted fungus.

Around mid-May, the red-eyed cicadas of Brood XIX will emerge from their underground lairs. They are considered the largest periodical cicada group and come out every 13 years. As that brood disappears, Brood XIII will emerge. This group comes out every 17 years.

The 13-year Brood XIX, sometimes known as the “Great Southern Brood,” will emerge across Alabama, Arkansas, Georgia, Illinois, Indiana, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee and Virginia.

The 17-year periodical cicadas in Brood XIII will be less widespread, emerging only in Indiana, Illinois, Iowa, Wisconsin and potentially Michigan.

What are zombie cicadas?

Some of Brood XIX is expected to surface with a fungus that turns them into hypersexual, frantically-mating zombies that spread the fungus like an STD and keep going until their genitals fall off, CBS News reports.

“The cicada continues to participate in normal activities, like it would if it was healthy,” Matthew Kasson, an associate professor of Mycology and Forest Pathology at West Virginia University, said. “Like it tries to mate, it flies around, it walks on plants. Yet, a third of its body has been replaced by fungus. That’s really kind of bizarre.”

Kasson says the cicadas may be able to ignore the fungus because it produces an amphetamine that could give it stamina.

He explained that the fungus causes the cicadas to exhibit hypersexual behavior.

“Males for example, they’ll continue to try and mate with females — unsuccessfully, because again, their back end is a fungus. But they’ll also pretend to be females to get males to come to them. And that doubles the number of cicadas that an infected individual comes in contact with,” he said.

How cicadas become infected

Both broods of the periodical cicadas can be infected by the fungal pathogen Massospora cicadina, according to Kasson.

After the cicadas emerge from the ground, they molt into adults. If they are infected with the fungus, the backside of their abdomens opens up, and a chalky, white plug erupts out, taking over their bodies and making their genitals fall off in the span of a week to 10 days.

Usually, male cicadas let out a loud humming sound to attract female cicadas, and the female flicks her wings to signal she wants to mate. But the fungus causes males to flick their wings like females to attract males and, in turn, infect them, Kasson explains.

The fungus Massospora cicadina produces spores on the cicadas. It is suspected that when they die, the spores absorb into the soil and infect other cicadas underground.

Are zombie cicadas dangerous?

Though the ‘Cicada-geddon’ is expected to bring trillions of red-eyed bugs out from the ground, only around 5% of them are expected to be infected with the fungus.

According to experts, cicadas, even the hypersexual fungus-riddled ones, are perfectly harmless to humans and animals.

Outside their loud singing being somewhat of a nuisance, cicadas pose no threat.