Love is in the air this spring in the eastern United States, where billions of cicadas will soon appear in the biggest emergence event since 2004.
The insects are part of a group called Brood X — also known as the Great Eastern Brood — which is expected in a geographical range stretching from Tennessee to New York.
These cicadas have been subterranean for 17 years, tunneling and feeding beneath the soil. When they are back above ground, finding a mate will be, understandably, a top priority. The loud, buzzing drone cicadas make is actually a mating song emitted by male insects, flexing a drumlike organ called a tymbal.
"It's all boys calling girls," said entomologist Eric Day of Virginia Polytechnic Institute and State University extension. "First you get a few here and there, then what happens is they start chorusing — there's so many of them that the cicada calls all combine in this huge chorus."
While cicadas can be a nuisance for some orchardists and farmers, witnessing them is also an awe-inspiring experience, Day said.
"This is a real treat. This is an unusual biological phenomenon. Periodical cicadas only occur in the eastern United States; they don't occur anywhere else in the world," he said. "It's just going to be an amazingly big, big show."
When and where will the cicadas emerge this year?
That show doesn't kick off until the ground warms up. Cicadas, which are not harmful to humans or animals, begin to emerge when the soil reaches 64 degrees Fahrenheit, Day said.
A few individuals will probably come out in mid-to-late April, Day said, stragglers that the entomologist nicknames "lonesome Bobs," who call and call to no avail. The true, large-scale emergence might happen in the first or second week of May, depending on location.
Scientists differ about the precise range of Brood X cicadas, but entomologist Gene Kritsky, dean of behavioral and natural sciences at Mount St. Joseph University in Cincinnati — and the unofficial dean of Brood X cicadas — expects to see them in 14 states plus the District of Columbia.
Brood X — the "X" is the Roman numeral for 10 — is the largest group of 17-year cicadas, said Kritsky, author of the new book "Periodical Cicadas: The Brood X Edition." (Other periodical cicada groups emerge on a 13-year cycle.)
Scientists don't know the precise reasons behind the cicada schedules, or why both kinds of periodical cicadas have prime-numbered life spans. Emerging en masse, though, helps the bugs survive predation and mate successfully, as birds and small mammals only can pick off so many cicadas at once.
When it comes to such reproduction strategies, this year's cicadas have a lot in common with other broods. What sets Brood X apart from other cicada emergences, however, is proximity to large metropolitan areas.
"About 35 million Americans will have the opportunity to interact with Brood X," Kritsky said, noting that they will likely be spotted in Philadelphia; Washington, DC; Baltimore; Cincinnati; and Indianapolis. In the past, Brood X cicadas have even emerged in New York City's Central Park.
Early signs of cicadas include finger-size holes in the ground near the base of trees. You might also spot a chimneylike tunnel poking out of the soil.
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When the insects do appear, they make an impressive amount of noise. Once, Kritsky said, he recorded a cicada chorus while sitting in a cemetery below the flight path for Cincinnati/Northern Kentucky International Airport in Hebron, Kentucky.
The insects clocked in at 96 decibels, drowning out the sound of passenger jets passing directly overhead. The chorus won't last long, however. Cicadas usually die just four to six weeks after emergence.
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