The Brood X cicadas arrive by the billions

The air pulses with a slow throbbing shriek as billions of red-eyed critters emerge from underground and swarm everything. What sounds like a horror movie is simply Brood X: cicadas that emerge once every 17 years in the eastern and mid-western United States.

The cicadas, which can grow up to 5 centimeters in length but are harmless, make their appearance in late May and June in 15 U.S. states. While different broods of periodical cicadas exist, Brood X is one of the largest.

The United States is the only country where cicadas stay underground for 13 or 17 years, University of Connecticut entomologist John Cooley tells the Associated Press.

Left: A cicada emerging from its shell. Top right: A man holding a bag full of cicadas. Bottom right: A woman eating a roasted cicada on a toothpick (© Chip Somodevilla/Getty Images)
Clockwise from left: A cicada emerges from its shell on May 17 in Takoma Park, Maryland. A man collects cicada nymphs in Takoma Park May 18. A woman tastes a roasted cicada May 22. (© Chip Somodevilla/Getty Images)

Michael Raupp, of the University of Maryland’s Entomology Department, describes the cicadas emergence as one “of the craziest life cycles of any creature on the planet.”

The cicadas emerge, shed their skin, climb trees, sing, mate and lay eggs.

“Remember, these are just teenagers and they’ve been underground for 17 years,” Raupp told National Public Radio. “It’s been a dismal existence. They want to come up and party.”