Billions of Brood X cicadas set to emerge in parts of Eastern US for first time in 17 years: What to know

Periodical cicadas emerge from underground in the spring of their 13th or 17th year. Fifteen US states, and Washington, DC, are about to see a whole lot of them.  

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Parts of the Eastern United States will soon witness quite a buzz-worthy sight: billions of cicadas emerging from underground for the first time since 2004 to swarm outdoor spaces and share their collective mating calls. 

Periodical cicadas, as they’re known, spend almost their whole lives a foot or two underground, living on sap from tree roots. Then, in the spring of their 13th or 17th year, mature cicada nymphs emerge for a short adult stage, synchronously and in huge numbers. Really huge numbers. 

“They may amass … in parks, woods, neighborhoods and can seemingly be everywhere,” Michigan State University entomologist Gary Parsons explained in an MSU question and answer session on the phenomenon last year. “When they are this abundant, they fly, land and crawl everywhere, including occasionally landing on humans.” 

Here are answers to some of the main questions about this spring’s big cicada emergence. 

What is Brood X? 

The Eastern United States is home to six species of periodical cicadas that emerge in different years. 

This spring, it’ll be time for members of one of the largest broods of 17-year cicadas, known as Brood X or the Great Eastern Brood, to burrow out from their subterranean hideouts and show off their black bodies and bold red eyes. Expect to see all three 17-year species: Magicicada septendecim, Magicicada cassini and Magicicada septendecula.  

Which states will be impacted? 

Parts of 15 states, as well as Washington, DC, will hear the romantic serenades of males in trees, trying to attract females. The states are Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, North Carolina, New Jersey, New York, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia.  

When will the cicadas emerge? 

The return of the cicadas typically starts around mid-May (though it could come earlier) and runs through late June. It is, needless to say, a wild spectacle. Some people view the insect invasion as an annoyance, while others welcome it as a wonder of nature. Some in the latter category even travel around the US to cicada emergence areas to experience the sights and sounds annually and help scientists map cicadas. 

A free app called Cicada Safari, available for iOS and Android, lets the cicada-curious record periodical-cicada sightings. They can also record sightings at the websites Cicada Mania and iNaturalist, a joint initiative of the California Academy of Sciences and the National Geographic Society. Cicada mapping helps scientists verify periodical the insects’ life cycles, as well as broods’ relationships to one another, to gain a better understanding of biodiversity, biogeography and behavior and ecology

Because Brood X occurs four years after Brood VI and four years before Brood XIV, and the three broods are adjacent to each other in parts of their geographic ranges, cicada trackers may spot “stragglers” from other broods this year. “From a biological perspective, four-year stragglers from either of these broods are of interest because they can cause gene flow among these broods,” the University of Connecticut explains. “From a practical perspective, four-year stragglers from any of these broods complicate mapping efforts, because populations may be difficult to assign to a brood.”  

 Stragglers may confuse mapping efforts, but the university stresses that “a misleading map is worse than no map at all.”

Can the bugs harm me? 

The bugs are harmless, Parsons stresses, and typically don’t come indoors, though they do gather on outside walls. 

“The only way they could get inside is accidentally flying in through an open door or window, or because they had landed on a person who then carried them inside unnoticed,” Parsons says. 

Why do so many come out at once? 

It’s thought that by emerging en masse, the bugs ward off predators so enough can live on to mate. Strength in numbers and all that. 

The cicadas typically begin to come out when soil temperatures 8 inches (20 centimeters) underground reach 64 degrees Fahrenheit (18 degrees Celsius). “That seems to be the trigger that causes them all to emerge over a few days or weeks in one area,” Parson says. A warm rain often triggers their emergence. 

Because periodical cicadas are sensitive to climate, patterns of different broods and species reflect climatic shifts, note John Cooley and Chris Simon, professors of ecology and evolutionary biology at the University of Connecticut. 

“For example, genetic and other data from our work indicate that the 13-year species Magicicada neotredecim, which is found in the upper Mississippi Valley, formed shortly after the last glaciation,” they write in a piece for The Conversation. “As the environment warmed, 17-year cicadas in the area emerged successively, generation after generation, after 13 years underground until they were permanently shifted to a 13-year cycle.”

How long will they stick around? 

For about four weeks. Godspeed, Brood X. 

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