’Tis the cicada season

It’s about to get loud. Fifteen eastern U.S. states and the District of Columbia are expected to play host to billions of harmless and hapless black-bodied, red-eyed bugs anytime from late April until early June. But they won’t be around for long. Though they’ve spent the better part of two decades underground, the Great Eastern Brood of periodical cicadas will break free from underground tunnels, climb trees, and deliver mating calls that can be louder than a lawnmower—all within four to six weeks before dying.

Scientists call the group Brood X. Collectively, the bugs represent one of the largest of 15 periodical cicada broods that emerge every 17 years. In 2004, scientists spotted the brood as far east as Pennsylvania and as far west as Illinois. Entomologists have identified Pennsylvania, Indiana, Maryland, and Washington, D.C., as major hot spots for the bugs. In some places with heavy concentration of nymphs, there could be as many as 1.5 million cicadas per acre, or about 34 per square foot, according to entomologists at Virginia Tech.

The parents of this year’s cicadas emerged in 2004, laid eggs, and quickly died. Since then, those eggs have hatched into nymphs that feed on tree roots. Depending on the weather, the bugs will surface sometime between late April and early June—whenever soil temperatures 8 inches below the surface reach about 64 degrees, scientists say. The nymphs that emerge quickly clamber up trees or anything else that gets them away from ground-based predators.

Scientists believe cicadas coordinate their emergence as a survival strategy called predator satiation. The species is mostly defenseless against predators during its just weeks-long life cycle above ground. But with so many emerging at once, the bugs can overwhelm the appetites of reptiles, birds, and small mammals. Once the predators have had their fill, the remaining cicadas can get on to mating.

According to cicada expert and Mount St. Joseph University entomologist Gene Kritsky, weather conditions must be right for the cicadas to emerge. “For the past couple of years, it’s been the second day that our temperatures have reached the low 80s,” Kritsky told the Cincinnati Enquirer. “Then they pop.”