States along the East Coast are preparing for a rare and spectacular natural phenomenon. As spring sets in and the soil warms, the ground will erupt as billions of cicadas burst from the earth.
It’s an event nearly two decades in the making. Known as Brood X, this massive swarm has been biding its time underground for the last 17 years.
Brood X is part of a special group of cicadas called “periodical cicadas,” known for their singular life cycles. Depending on the brood, they emerge only once every 13 or 17 years.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
As the sun warms their wings for the first time, these jewellike insects zero in on a single goal: generating the next brood. They’ll spend a few short weeks swarming nearby trees and finding mates. Then, after laying their eggs in the branches, they’ll die—a swift and brutal conclusion to their exceptional lives.
Meanwhile, the eggs will hatch and the nymphs will fall to the ground, burrow into the soil and find nutritious tree roots to feed on. There, they’ll begin their long wait in the dark.
There are only 15 periodical broods in the world, all of them found exclusively in the eastern United States. Brood IX, another 17-year swarm, emerged last year across North Carolina, Virginia and West Virginia. Brood VIII came out the year before.
These are some of nature’s most well-timed events—humans have been documenting them for hundreds of years. But they could be shifting over time.
Sometimes, members of a brood come out before their time. It’s happened throughout history—early emergences have been documented as far back as the late 19th century, according to Gene Kritsky, a cicada expert at Mount St. Joseph University in Ohio.
But there seem to have been a spree of these early events in recent years, he added.
In fact, a small segment of Brood X emerged early in 2017. Thousands of cicadas were sighted in the Washington area that year, a full four years before they should have come out.
Scientists are still working to better understand what triggers these events and why they sometimes get out of sync. Climate-related factors may play a role.
If that’s the case, that means climate change has the potential to affect the timing of these events in the future, some experts say—potentially causing long-term changes in the 15 broods down the line.
“This is happening all the time now,” Kritsky told E&E News.
Kritsky has been documenting and mapping periodical cicadas for decades. He’s seen early emergings happen in multiple broods from Pennsylvania to Georgia over the years, and he believes climate-related factors are largely to blame.
“These accelerations that we’re seeing constantly for all these different broods over much of the eastern half of the U.S., the only common phenomenon that can account for it is climate,” he said.
Counting the years
Periodical cicadas are something of a scientific enigma, even today. Scientists still aren’t totally sure why they evolved their long life cycles in the first place.
Some experts believe the adaptation arose as a way to avoid predators, said John Cooley, a cicada expert at the University of Connecticut. Others believe it happened in response to glacial cycles, a way to cope with ice ages.
Tens of thousands of years later, periodical cicadas are still emerging like clockwork every 13 or 17 years. Scientists believe certain cues in the roots of the trees they feed on help them “count” the years go by.
“These plants lose their leaves in the fall and grow new ones in the spring,” Cooley said. “So there must be a host of different signals going on and indications in the plants of what’s going on.”
Multiples of four seem especially important in the counting process, although scientists aren’t sure why. When cicadas emerge early, it’s most often by four years. That’s what happened to Brood X back in 2017.
In these cases, scientists believe something must be happening to throw off the count.
So far, there isn’t any definitive proof of what’s going on. But climate factors may have something to do with it, Kritsky said.
False springs sometimes happen toward the end of mild winters, he pointed out. That’s when the weather warms up just enough for trees to start leafing early. These events are often followed by at least one more freeze before spring sets in for good.
When that happens, Kritsky hypothesizes, it could trick the buried cicadas into thinking that more than one year has passed.
If he’s right, then these early emergings could happen more frequently in the future. Numerous studies suggest spring is already coming earlier across much of the United States as the climate warms.
But it’s a difficult question to investigate. Periodical cicadas are challenging to study, precisely because they have such long life cycles. It could take decades to figure out whether there are any long-term changes happening in their behavior.
Still, it’s worth monitoring.
For one thing, periodical cicadas draw strength in numbers. Individually, they’re easy targets for birds and other insect-eating animals; they’re large, flashy and easy to spot. Swarming out by the billions gives them an advantage against predators—it increases the odds that enough of them will survive to carry on the next generation.
Early emergings can potentially divide cicada populations and make them more vulnerable. The early ones often come out in relatively small groups, according to Kritsky—and they’re often quickly gobbled up by predators.
When the rest of the population comes out on time, it’s slightly smaller than it should be.
With Brood X, for example, “for everyone that came out in 2017, that was one fewer cicada that’s gonna come out this year,” Kritsky said.
That said, it doesn’t look like the recent early events have caused any major trouble for the broods so far, Kritsky added. But it’s worth keeping an eye on.
There’s also the possibility that bigger splits could cause entirely new broods to arise. If part of a brood emerges early in large enough numbers to reproduce, the next generation might be permanently out of sync with the original brood—a new population entirely.
For now, these are mostly just hypotheses about the future. But scientists are getting better at monitoring cicada activity, which may help them better understand how these animals are responding to a changing environment.
Kritsky and colleagues at Mount St. Joseph University have developed an app called Cicada Safari, where anyone—scientists and non-scientists alike—can document their cicada sightings. The data can help researchers keep tabs on where different broods are located, when they’re emerging and whether any of these things are changing over time.
While plenty of questions remain, Cooley says it’s important to soak up the magic of this year’s event.
“There aren’t really any other places in the world that you can go and see something like that,” Cooley said. “So sit back and enjoy it, because it’s unique.”
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.