Hordes of winged cicadas are coming out and turning up the music for their biggest party in 17 years, stretching from North Carolina through Virginia to New York - but experts aren't yet sure just how big the party will get.

Billions of the bugs are climbing out from the ground as the spring weather warms up and soil temperatures reach the magic turning point of 64 degrees Fahrenheit (18 degrees Celsius). The warm-up has just reached the proper level in the Northern Virginia suburbs of Washington, D.C., according to Sutron's closely watched temperature tracker.

That assessment is confirmed by on-the-ground eyewitness reports registered on Magicicada.org and Radiolab's Cicada Tracker. John Cooley, an expert on cicadas at the University of Connecticut, took in the full cicada buzz this week during a field trip to Lynchburg, Va. "We've had some good, rip-roaring choruses," he told NBC News.

These Brood II cicadas spend most of their 17-year life cycle underground, patiently nourishing themselves on fluids from plant roots, and then arise for a frantic weeks-long cycle of crawling, flying, mating, egg-laying and dying. When the mating party really gets going, the thrum of the cicadas' call can get as loud as 90 decibels.

"It'll be as loud as a rock concert," University of Maryland entomologist Michael Raupp told NBC News, "but hey, these are teenagers. they've been underground for 17 years. They're going to get in trees, they're going to sing."