When the ground warms to 64 degrees Fahrenheit, a group of cicadas known as Brood II will infect the East Coast from North Carolina to New York's Hudson Valley. NBC's Anne Thompson reports.





After hanging around underground for 17 years, billions of flying bugs known as cicadas are due to sweep over the East Coast starting sometime in the next month. And although it's too early to predict exactly where or when the brood will appear, this spring's emergence should rate as the most closely watched bug-out in history.

"For entomophobes, this is the season of despair. For the entomophiles, this is the season of joy," said University of Maryland entomologist Michael Raupp, using highfalutin terms for bug-haters and bug-lovers.

The outbreak is expected to start in the Carolinas in April or early May, and work its way up northward to Washington, Philadelphia and New York by early June. Some observers have already reported the first signs of the emergence. The timing depends on the weather: Cicadas dig "escape chimneys" up from the ground where they've been maturing for the past 17 years — and when the temperature reaches 64 degrees Fahrenheit (18 degrees Celsius), that signals the insects to rise up, wriggle out of their shells, take wing and look for mates.

Be ready for the buzz

The bugs are mostly harmless to plants and humans. The worst a cicada can do is poke you with its pointy proboscis. But the 90-decibel buzz of a sky-darkening swarm can be a bit unnerving to the unprepared. Raupp recalls one harrowing tale from 1962's outbreak, when "the kids were shrieking in the playgrounds as cicadas divebombed them."

In Raupp's view, however, the pluses far outweigh the minuses. The cicada nymphs help aerate garden soil with their burrowing, and when they emerge, the bugs represent a culinary bonanza for birds and other species. (They're said to taste like asparagus. Or shrimp.)

Besides, cicadas are cool. "Without a doubt, they are a true marvel of nature and one that should be enjoyed whenever possible," Raupp writes on his Bug of the Week blog.

University of Connecticut researcher John Cooley tells NBC's Anne Thompson cicadas are "noisy and active."

It's thought that the 17-year life cycle arose to keep the cicadas' predators off their game, and perhaps make the most of climatic variations. Scientists even suspect that the number 17's status as a prime number plays a role. (Some periodical cicada species emerge every 13 years, and 13 is also a prime number.)

This particular group of cicadas, known as Brood II, hasn't surfaced since 1996. But other broods have had their own day in the sun during the intervening years. The big ones include Brood X ("The Big Brood"), which last came out in 2004; and the 13-year Brood XIX ("The Great Southern Brood"), which emerged in 2011.

The buzz online

This year's brood is notable in that it should spread out over the United States' most densely populated region. Entomologists expect the cicadas to show up in the countryside, in woodsy suburbs and even in urban locales such as New York's Central Park.

The New York-based Radiolab science show is preparing for "Swarmageddon" by helping citizen scientists build soil thermometers. Readings from the "cicada detectors" are being shared via an interactive Cicada Tracker map. Meanwhile, the Magicicada website keeps up its own database of cicada sightings. That website, supported by the National Geographic Society, also provides tons of information about the species and what to do with them. (But if it's recipes you need, you might have to look elsewhere.)

Thanks to the rapid rise of crowdsourcing and social media, this year's event is sure to become the most tweeted cicada emergence in history: Cicada Mania suggests using the hashtag #BroodII for the 2013 outbreak, and #Cicadas for general cicada issues. If you want to see the Twitterverse from the cicadas' point of view, just follow @Brood_II. There's a Cicada Mania Facebook page for entomophiles. And if you're an entomophobe, you'll find kindred spirits on the "I Hate Cicadas!!!!!!" Facebook page.

Whether you're an entomophobe or an entomophile, this will all be over soon: Once it starts, the emergence typically lasts only four to six weeks — long enough for Brood II's cicadas to mate, lay their eggs, and get the next generation settled for their 17 years of life underground as root-sucking nymphs.

Slideshow: Return of the cicada Take a closer look at the curious 17-year life of the flying bug as the East Coast prepares for an invasion. Launch slideshow

More about cicadas:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.