Billions of cicadas lurking underground in the Hudson Valley and along the East Coast are awaiting their cue: when ground temperature reaches exactly 64 degrees.

Only then will the inch-long creatures crawl out of the burrows they have lived in for 17 years, climb trees and begin several weeks of riotous mating calls, sex, parenthood and finally death. Then the insects’ offspring will crawl underground to begin the cycle over again.

In the Hudson Valley, showtime could come within days as the air temperature climbs and the earth warms.

Scientists say the cicadas with bulging red eyes will outnumber people from North Carolina to Connecticut by about 600-to-1 and that the males’ mating calls will be as loud as a rock concert.

In 2004, Gene Kritsky, an entomologist at the College of Mount St. Joseph in Cincinnati, measured cicadas at 94 decibels, saying it was so loud “you don’t hear planes flying overhead.”

Cicadas come out every year in different regions around the world, but the variety about to make their entrance along the East Coast are different. They’re called magicicadas — as in magic — and are red-eyed. Magicicadas are found exclusively in the eastern half of the United States.

There are 15 U.S. broods that emerge every 13 or 17 years, so that nearly every year some place is overrun. Last year it was a small area, mostly around the Blue Ridge Mountains of Virginia, West Virginia and Tennessee. Next year, two places get hit: Iowa into Illinois and Missouri; and Louisiana and Mississippi. Still, it’s possible to live in these locations and actually never see them.

This year’s invasion is one of the bigger ones. Several experts say that they really don’t have a handle on how many cicadas are lurking underground but that 30 billion seems like a good estimate. At the Smithsonian Institution, researcher Gary Hevel thinks it may be more like 1 trillion.

Even if it’s merely 30 billion, if they were lined up head to tail, they’d reach the moon and back.

This year’s invasion, dubbed Brood II by scientists, is expected to cover large swaths of the Hudson Valley, according to Daniel Gilrein, an entomologist with Cornell Cooperative Extension of Suffolk County. Nature lovers, he said, should plan expeditions in late May and early June to see the insects at work.

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