Brood X has emerged in full force. Now, when will the cicadas go away?

Trillions of periodical cicadas are tunneling out from their underground homes for the first time in 17 years to mate, loudly. Your questions, answered.

Leslie Katz Former Culture Editor
Leslie Katz led a team that explored the intersection of tech and culture, plus all manner of awe-inspiring science, from space to AI and archaeology. When she's not smithing words, she's probably playing online word games, tending to her garden or referring to herself in the third person.
  • Third place film critic, 2021 LA Press Club National Arts & Entertainment Journalism Awards
Leslie Katz
6 min read

Brood X cicadas in Haverford, Pennsylvania, on May 25.

Jim Watson/Getty Images

Now that Brood X cicadas have tunneled out from their subterranean homes across the Eastern US, you might wonder when they'll be leaving. Here's everything you need to know about the little critters with black bodies and bold red eyes now making their inescapable appearance.   

What is Brood X? 

In case you're new to Brood X, it's a group of periodical cicadas, which are different than annual cicadas. They 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, depending on the type, mature cicada nymphs emerge for a brief adult stage, synchronously and in huge numbers. They mate and then die, and their newly hatched offspring drop to the ground and burrow in for the next 13 or 17 years.  

A newly emerged periodical cicada sheds its exoskeleton and unfurls its wings. Soon it will be mating time. 

GIF by Leslie Katz/CNET

Groups of cicadas that share the same emergence years are known as broods. Bugs belonging to one of the biggest broods of 17-year cicadas, called Brood X or the Great Eastern Brood, are making their appearance now. 

After emerging, the insects climb up the nearest vertical surface. They shed their exoskeletons and inflate their wings. After a few days resting and waiting for their shells to harden, the mating begins. The burst of activity is impossible to miss once males start emitting their high-pitched mating song. That happens via sound-producing structures called tymbals on either side of their abdomen. 

The mass mating lasts at least three to four weeks. Soon after, the newly hatched nymphs crawl to the edge of the tree branches where the females laid their eggs, drop to the ground and burrow in for the next 17 years. And the cycle begins again. 

When will Brood X cicadas go away? 

The bugs typically begin to come out when soil temperatures 8 inches (20 centimeters) underground reach 64 degrees Fahrenheit (18 degrees Celsius), with a warm rain often triggering their emergence. Once above ground, they generally have a lifespan of four weeks, depending on the weather. Since the cicadas usually start emerging around early- to mid-May, they should start to die off by late June or early July. 

"Because the emergence was strung out over seven or more days do to variable weather, they may be out for five weeks in any given area or even a bit longer," says Chris Simon, a professor of ecology and evolutionary biology at the University of Connecticut. "They generally gradually taper off."

Brood X cicada emergence in photos: How it looks as trillions of bugs appear

See all photos

Where is Brood X coming out?     

Parts of 15 states, as well as Washington, DC, are hearing 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.  

United States Forest Service

Cooler weather than usual in parts of the US this year delayed their appearance in some places, and in others they're not showing up at all, due to development, pesticide use and invasive species. 

Residents in places where they've shown up in full force are busy sharing sights and sounds on social media. 

What do Brood X cicadas sound like? 

It varies by species, but their call can sound like a high-pitched electric buzz, a chirp or a rattle. (Hear it below.) The calls of a group of males can exceed 90 decibels, about the same level as a motorcycle at 25 feet (about 8 meters) away. The females respond to the males' come-hither calls by clicking their wings, and all the back and forth makes for a distinctive symphony. 

"If you are not living in a place with cicadas, I can best describe the noise as broken car alarm crossed with UFO landing," one Twitter user in Washington, DC, shared. Hear the sounds for yourself in the videos above or the audio below. And before calling 911, please make sure it's cicadas you're hearing, and not a car or house alarm. 


Can cicadas hurt humans? What about trees?  

Nope, the insects are harmless. They don't sting, bite or carry diseases, and they typically don't come indoors, though they do gather on outside walls. 

Enlarge Image

Exoskeletons left behind by newly emerged 2021 Brood X cicadas decorate a tree in Annapolis, Maryland. 

Russell Holly/CNET

"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.  

During dense emergences, females can lay enough eggs in branches to damage young trees, but the abundant egg-laying also naturally prunes trees, resulting in more flowers and fruit in the years that follow. The cicadas boast other ecological benefits as well. Periodical cicadas aerate large amounts of soil when they emerge en masse, and when they die, their decaying bodies enrich the ground with nutrients.

Here's what you need to do to get your lawn and trees ready

Can pest control pros help me? 

When people call for help during cicada emergence, those in pest control are largely in the position of educating clients about why the pest pros aren't going to show up and spray down their yard with pesticide. 

"We really want people to understand and know that pesticides are not the answer, which sounds really funny coming from a pest control company," Frank Meek of pest control company Orkin tells my CNET colleague Erin Carson. "Pesticides are not the thing to use on this insect. They don't work for it, and it's a waste of product, and it's a danger to the environment just to spray down because you're afraid of the cicadas."

Why do so many cicadas come out at once? 

It's thought that by emerging in such huge numbers, enough of them can avoid predators and live on to mate -- basically, strength in numbers.  

What can scientists learn from mapping cicadas? 


Through the app Cicada Safari, citizen scientists can help map the insects. 

Cicada Safari

Some people view the mass of insects as a pesky annoyance, but others welcome it as an awe-inspiring wonder of nature. Some in the latter category even regularly travel around the US to cicada emergence areas to experience the sights and sounds and help scientists map the creatures. 

Cicada mapping helps scientists verify the periodical insects' life cycles, as well as broods' relationships to one another, to gain a better understanding of biodiversity, biogeography and ecology. 

A free app created at Cincinnati's Mount St. Joseph University, called Cicada Safari and available for iOS and Android, lets citizen scientists 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. 

Because periodical cicadas are sensitive to climate, patterns of different broods and species reflect climatic shifts, note John Cooley and 

"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."

Because Brood X occurs four years after Brood VI and four years before Brood XIV and because the three broods are adjacent to one another 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."

Godspeed, Brood X.