Don’t freak out, but the cicadas are coming — lots of them

Billions will likely emerge across the eastern half of the US this spring, but climate change is a wild card

March 13, 2024
A close up image of a cicada
Periodical cicadas stay in the ground for 13-17 years. Then, they emerge all at once. This year two broods will emerge at once. [Credit: Sagar Vasnani, Unsplash

Roasted and dipped in chocolate, sautéed in teriyaki sauce or mixed into chocolate chip cookies—there are endless ways to cook up cicadas. Martha Weiss, a biologist at Georgetown University, is already thinking about the cicada dishes she’ll make for a viewing party she’s planning this spring in Illinois. 

Weiss will gather along with other cicada enthusiasts to view history in the making: for the first time since 1803, two broods of periodical cicadas will emerge at the same time in the Eastern U.S. 

The broods, which are groups of cicadas in a particular region that emerge together, won’t overlap — except possibly in a small sliver in northern Illinois. But residents across much of the East can still expect to see “millions per acre” starting in late April or early May, says John Cooley, who studies cicadas at the University of Connecticut. “You won’t be able to avoid these,” he says.  

Cicada Brood XIII has been in the ground for 17 years and will emerge in Iowa, Illinois, Indiana, Wisconsin and Michigan. Brood XIX, in the ground for the past 13 years, is one of the largest, spanning Maryland to Georgia on the East Coast and Iowa to Oklahoma in the Midwest. 

This year’s twin emergences will come with extra intrigue thanks to climate change. Temperature and other environmental cues play a key role in the unusual life cycle of the red-eyed insects, which spend many years tunneling underground and feeding on tree sap before finally emerging to climb trees, sprout wings and lay their eggs.

The potential for climate change to disrupt these environmental cues is, “absolutely concerning to me,” Cooley says, explaining that the consequences of a failed cicada emergence would ripple through their forest habitats for years afterward. He says deforestation in newly developed suburbs has already prompted strange behavior by cicadas during recent emergences, including cases of the insects trampling and killing each other as they rush to climb scarce trees. 

“Cicadas,” Cooley adds, “are canaries in the coal mine for the health of our Eastern forests.”

The insects, which are up to two inches long, stay above ground for just over a month — long enough to lay the eggs of their next generation. Their evolutionary secret is emerging en masse, increasing the likelihood that their predators can’t possibly eat all of them. Baby cicadas, called nymphs, hatch only to fall to the ground, where they crawl back into the earth to mature slowly over years. 

There are a surprising number of animals who will eat cicadas. Foxes, rats, turkeys and others (including a few brave humans) will take advantage of the suddenly abundant food source — which will only be more abundant this spring. 

During a cicada emergence in 2021, researchers found that over 80 species of birds shifted their diets primarily to cicadas instead of caterpillars. With greater numbers of caterpillars left uneaten, the researchers observed increased damage to leaves. 

While cicada emergence is “a short-term phenomenon, it can have a big effect. And it can last for years,” says John Lill, a biologist at George Washington University and co-author of the study on the 2021 emergence. 

Years when cicadas emerge have been tied to lower acorn production from oak trees, likely due to the damage inflicted when cicadas slice open tree branches to lay their eggs. But the reduction in acorns is typically followed by a surge two years later, a phenomenon playing out right now in Washington, D.C. 

More acorns mean more food for rodents like chipmunks and rats. And with more food, rodents are able to reproduce more, increasing their populations. This domino effect has been linked to increased rates of Lyme disease, which these animals can spread. 

While cicadas can change food web dynamics and affect growth patterns of plants, it’s a two-way connection: The bugs are equally affected by the environment around them, particularly by trees, which they rely on to know when to emerge. 

Rather than counting time, cicadas track when sap starts and stops flowing into tree roots. When the right number of tree life cycles have gone by (it’s still a mystery how they all agree on this, Lill says), a brood will start digging tunnels up to fresh air. When the ground temperature reaches around 64 degrees Fahrenheit, they’ll emerge. 

“You’ll see an army of little shrimp-like creatures crawling up out of the soil. They’re marching across the sidewalk and they’re climbing up trees and stop signs and mailboxes and car tires,” Weiss says. Then, they find a place to perch and start their metamorphosis into winged adults. 

But as the climate warms, the cycles of trees could be changing, altering the signals cicadas depend on. 

In one experiment, conducted at the University of California, Davis, researchers sped up the life cycle of trees to test if that really determined when cicadas emerged. Sure enough, cicadas emerged on track with the sped-up timeline. If tree life cycles are altered due to climate change, with longer growing seasons from warmer weather, it could change when and how cicadas emerge, with possibly detrimental effects. 

“You think, ‘Oh, there’s so many of them, nothing could ever happen to them,’” Cooley says. “But yes, it can. You tweak the habitat, you tweak the rules of the game, and maybe you send them into a death spiral. If their populations get below some threshold, they get wiped out by predators and they’re gone,” Cooley adds. 

It’s not uncommon for some cicadas, called stragglers, to emerge off-cycle — either before or after their brood. But if only a few emerge off-cycle, their chances of survival are extremely low. 

More stragglers have been reported in recent years, but there’s some debate over whether there are actually more, or if the higher numbers are a result of better record-keeping, says Cooley. If there are indeed more stragglers, it could mean that cicadas are able to form broods off-cycle and may emerge more regularly. 

The loss of trees in urban and suburban areas could also be bad news for cicadas. In 2021, Cooley observed something novel: cicadas that emerged in suburban lawns with only a few trees trampled and killed each other. With so little space to share, cicadas disrupted the emergence process of their own kin, causing “mass death,” Cooley says. 

This won’t be as much of a problem in older green suburbs, like the ones in Chicago where the cicadas will emerge. But newer suburbs with less trees could see lower survival rates for cicadas. 

In Illinois this spring, Weiss and Lill will be looking at how cicadas affect another insect: ants. They’re curious to see how ants shifting their diets to cicadas could have ripple effects on the larger ecosystem. Weiss will also be investigating how cicadas choose where they lay their eggs and how nymphs navigate their surroundings. And of course, she’ll be sharing her cicada snacks which, she notes, are full of protein. 

Cooley, meanwhile, will be driving around with the windows open, using a GIS data logger to map cicada locations. His custom-designed logger listens to the high-pitched song of cicadas and estimates their density. Anywhere a cicada is found becomes a dot on his maps, which anyone can contribute to by reporting cicada sightings on the Cicada Safari app.

Cooley collects this data with the uncertain future of cicadas in mind. “If something has actually changed, we need to find that out,” he says. “Because that’s a sign of a breakdown in the ecosystem.” 

About the Author

Carrie Klein

Carrie Klein is a science journalist who loves to write about climate solutions and renewable energy. She comes to journalism with a background as a Communications Director for an environmental nonprofit and an undergraduate degree in English and Environmental Studies.


1 Comment

I am so excited about this event! Cicadas are so fascinating! Several years ago I was lucky enough to photograph a Cicada emerging from its shell and I have created a mug to commemorate this happening. Below is a link, I loved your informative article, I hope you will take a look at my mug and pass the link along!

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