Discoveries
07.08.2021

Signs of the Times

Despite their perceived abundance, the periodical cicadas that emerged across the eastern United States this summer point to a growing set of threats facing both the insects themselves and the ecosystems they help support.

Under the canopy of a regal oak, Gene Kritsky points his camera at the tree’s trunk, the lens nearly touching the bark. “Well, hello!” he says, snapping a photo of a Magicicada septendecim. Here in Cincinnati, it’s the first truly hot day of the year; the sky has been blue and cloudless all afternoon, sending the temperature soaring into the 90s. It’s also the first day of Kritsky’s field research in Mount St. Joseph Cemetery, the first time in 17 years that Magicicada is due to emerge in the area.

“Oh, it’s nice to be back,” Kritsky says, walking over to another oak. This has been one of Kritsky’s research sites for nearly 40 years; he arrived at Mount St. Joseph University (affectionately called Mount St. Joe’s by locals) as an associate professor in 1983, and now serves as dean of the university’s School of Behavioral and Natural Sciences. In those years, Kritsky has established himself as one of the world’s foremost cicada experts—and with his well-groomed white beard and tortoiseshell glasses, he looks every bit the part of the distinguished entomologist.

He crouches close to the ground, examining a series of finger-width holes in the earth; this is where cicada nymphs had surfaced as soon as the soil became warm enough. (Their trigger is a temperature around 64 degrees Fahrenheit; this year, there were reports of cicadas emerging as early as April from soil warmed by nearby hot tubs or dryer vents.) From there, the nymphs look for something, anything, to climb. On the tree in front of us, dozens of cicadas are making their way up. Kritsky points out clusters of the insects on tree leaves 20 feet above our heads. “They’re all gathering at the top, just as happy as can be,” Kritsky says. Others have climbed to as high as possible on tall grass, bushes, and even the cemetery’s headstones. There, they molt into their adult form, leaving behind brown exoskeletons. Some of these remain stuck to twigs and leaves; others fall to the ground, forming a crunchy carpet around tree trunks.

 

Soon, there will be billions of these shells strewn across the eastern U.S. While there are 3,300 other cicada species in the world, North American periodical cicadas steal the show when they emerge. For one, they’re hard to ignore; they emerge in such numbers that people often confuse them with locusts, and their mating calls can reach upwards of 90 decibels, as loud as a motorcycle or lawnmower. (During past emergences, cicadas have nearly drowned out speeches from the likes of Theodore Roosevelt and Bob Dylan.) And then there’s their peculiar life cycle: North American periodical cicadas spend either 13 or 17 years developing underground, sucking sap from the xylem in tree roots, and when they finally emerge, they’re alive for just a few more weeks to mate. (“To live underground for 17 years, then emerge into the light and air to love and die reminds me of a Greek tragedy, a sad fate,” wrote a commenter on the website Cicada Mania, a clearinghouse for cicada facts and research.) Broods are grouped by the year in which they emerge, and of the twelve 17-year cicada broods, the one emerging this year—Brood 10, often written as Brood X—has the widest geographical range. Spanning 15 states, Brood X emerges in major urban areas like Washington DC, Philadelphia, Cincinnati, and Indianapolis, inspiring countless social media posts (“is it ok if my dog ate 3 cicadas?”) and a wealth of news stories.

When cicadas are in the spotlight, so is Kritsky. During the last cicada emergence in 2004, he was out in this same cemetery, shooting video with David Attenborough and Dan Rather. Today, he’s stuck with me, and his phone rings constantly: Reporters from Gizmodo and Voice of America want his expertise, and earlier, while we chatted in his office, he sat for a quick Zoom interview with a local TV station. Just the night before, Kritsky was the first item in late night host Jimmy Kimmel’s opening monologue. “This guy is ready to eat them,” Kimmel said, showing a photo of the scientist. “Dr. Kritsky said cicadas taste a lot like cold asparagus. . . my rule of thumb is I don’t eat anything listed as one of the plagues.”

Kritsky is clearly leaning into his momentary celebrity. While we’re chatting in his office, Andrew Rasmussen, a professor of biology at the university, walks by, and Kritsky introduces us. “Every 17 years you know of course is the busiest time,” he says. “Hey, I heard you were on Kimmel last night?” While Kritsky recounts the story, Tim Lawson, chair of the psychology department, pokes his head into Kritsky’s office. “People are going to start contacting you for recipes,” he says.

“I’ve been talking about recipes for two weeks! But in every one of my interviews, I say I don’t eat them anymore,” Kritsky replies.

I ask him why not. After nearly three decades of studying cicadas, had he just finally had his fill?

“Well, first of all, they’re in decline,” he says. “And I have evidence to show that.”

If you’ve heard the ear-splitting screams of periodical cicadas, seen an orgy of them squirming at the base of a tree, or walked through a cloud of lazy, slow-flying cicadas, it might be hard to imagine that they could be in trouble when there seem to be so many of them. Perhaps too many, if you ask some people. While some enthusiasts welcome mass cicada emergences, the general public seems eager to avoid them. When we first spoke in January, Kritsky said he’d already been fielding calls from people planning outdoor weddings or proms, asking for his advice about when to time their event to avoid the emergence. In the month before Brood X’s emergence, news stories offered tips for avoiding “the 17 year nuisances,” and shared concerns that the emergence could make outdoor dining “a total nightmare.” Cicada phobia has led to hospital visits, car accidents, and even a 1987 cicada robbery: two men threw a cicada—“which is big and ugly but harmless,” according to New London, Conn. newspaper The Day—to rattle a restaurant cashier, then stole $25 from the cash register. “If you did man on the street interviews, you’d find plenty of people who want to rain hot flaming death upon cicadas as far as you possibly could,” says John Cooley, a cicada researcher at the University of Connecticut.

In light of this anti-cicada sentiment, cicada researchers are eager to dispel myths and misconceptions about the insects. After my first email to Chris Simon, one of Cooley’s colleagues at the University of Connecticut, her reply included a document called “Magicada Media Faux Pas,” explaining why frequently used terms like “swarm,” “invasion,” and “plague,” are inaccurate in describing cicadas’ emergence. The term “overrun,” too, gives the wrong impression; Simon’s document says it “implies that they are imposing on us when in fact we are much more of an imposition on them—clearing their trees and building asphalt parking lots on top of them.”

 

But the tree-clearing cicada imposition began long before there was asphalt. Researchers believe modern periodical cicadas appeared right around the end of the last Ice Age, between ten and fifteen thousand years ago, and among Indigenous communities, stories featuring cicadas have been passed down since time immemorial. North American colonists made the first written observations of cicadas, but also set to work building houses, farms, and cities. In the process, they uprooted massive tracts of land across the eastern half of the continent, destroying cicada habitat as they went. Naturalists at the time had little clue what cicadas were, calling them “flies,” and they certainly had no clue or concern that they were uprooting cicadas’ homes. By all accounts, the cicadas were plentiful, perhaps too much so. One researcher sent on an expedition by the Swedish government mistook cicadas for locusts, which, he wrote, came out in “dreadful quantities.”

As deforestation and urbanization increased across the continent, it wasn’t long before cicada reports began mentioning an apparent decline. Brood XXI, a 13-year periodical cicada brood once found in Florida, disappeared after the 1870s. And during 17-year Brood XI’s emergence in 1903, Connecticut landowners told USDA entomologist Charles Marlatt about low numbers in their area and predicted that the population might disappear entirely. Unfortunately, they were right; the last known Brood XI emergence took place in Willington, Connecticut in 1954, and subsequent surveys during Brood XI years have turned up none.

Four years later, entomologist Frank Young published a paper about cicadas in the Proceedings of the Indiana Academy of Sciences. “There is no doubt that all of the broods have declined since the early settlement,” he wrote, noting that the 1953 emergence of Brood X appeared to be smaller than its 1936 emergence. Kritsky, one of Young’s students, carried on this work. In 2004, his surveys found that Brood X cicadas had disappeared from 24 counties in western Ohio and Indiana where they had been reported in the past. In general, Kritsky says, cicadas’ range seems to be growing patchier. “You could find a pocket here, and then need to go 3 miles to find more. It’s not the continuous range we used to have—it’s much more disjunctive.” Similarly, Brood VII cicadas, once plentiful across eight counties in upstate New York, are now found in only one. And a 2012 study of Brood XIII cicadas, just outside of Chicago, finds they’re also in decline.

Now, deforestation isn’t the cicadas’ only foe: Climate change could also contribute to habitat loss. The now-extinct broods have one thing in common: They are near the southern- and northern-most edges of the cicadas’ natural habitat. If climate change leads to more extreme weather—hotter summers, colder winters, bigger storms—that might make it more difficult for cicadas to survive.

“They’re going to be like the passenger pigeons of the insect world.”

— John Cooley, University of Connecticut

Despite the evidence of decline, Brood X cicadas are still plentiful—but researchers wonder how quickly that could change. When I ask Cooley if he thinks it’s possible cicadas could go extinct, he at first approaches the question with a scientist’s caution, enumerating the limitations and flaws of the data which suggests cicadas’ decline. But after five minutes of talking through cicadas’ threats—deforestation, climate change, pesticides—it’s clear Cooley has some concerns. I ask again: Could cicadas really disappear? “My hunch is absolutely—they’re going to be like the passenger pigeons of the insect world,” he says. “It’s the kind of species people are going to say there are so many, nothing could ever harm them, and then run around cutting down the forests, spraying pesticides, and then boom, they’re gone.” Like cicadas, billions of passenger pigeons called the eastern U.S. home. In 1813, John James Audubon, writing from Kentucky, estimated he saw more than a billion literally darkening the sky, but by 1900, the last wild passenger pigeon was dead. And like cicadas, passenger pigeons relied on abundance to survive. Theoretically, once a population dwindles, it may be reduced to the point of no return, edging closer to extinction. “I suspect they’re more vulnerable than anyone would assume,” says Cooley.

On its face, determining whether cicadas are in decline seems like it should be easy: Just compare historical maps to what we see now, and if there are fewer cicadas in fewer places than before, then they are in decline. But that only works if you’re sure the data is accurate—and researchers have reason to believe it’s not. “One of the main lessons we’ve learned from discussion in the literature [about insect decline] is how little we actually know,” says Louie H. Yang, an ecologist at the University of California, Davis. “It turns out even for widespread common species that come out every year, that are popular amongst the public, we just don’t have great data. We have remarkably little data for the kind of long-term, long time series, large spatial scale—the kinds of things we want to know that mark global population decline.”

The first cicada surveys were recorded in the mid-1800s. As you might imagine, the efforts were quite low-tech; for Brood X’s 1851 emergence, a Maryland doctor named Gideon B. Smith wrote to local newspapers with requests that their readers send him letters with any information about where they’d seen cicadas. Three emergences later, in 1902, the U.S. Department of Agriculture began their own surveys; a team led by entomologist Charles Marlatt sent out 15,000 postcards to areas where cicadas had been known to emerge, asking people to submit their sightings. Those data remain a primary baseline, still referenced by modern cicada researchers.

As technology improved, so did researchers’ surveying tools, including the automobile, which enabled scientists to cover greater distances and conduct their own surveys. Even today, researchers still embark on summer road trips in the name of science. A 2009 paper from Cooley detailed their methods: “We also listened for singing cicadas by driving slowly (<40 mph) along roads with car windows open.” If, after two minutes with the engine off, there were no sounds, they concluded there were no cicadas in the area. Some older-school methods have been passed down from mentors; Kritsky says Monte Lloyd, a prominent cicada researcher active in the 70s, taught him to count cicada emergence holes by putting spoons in each one, then counting them at the end of the season to estimate the number of nymphs in an area. (In the year 2000, Kritsky had put 880 spoons in the ground outside a dorm when he learned that Neil Armstrong was set to visit the university campus as a commencement speaker. “You are going to have this taken down by graduation, aren’t you?” the school’s president asked him—clearly more a command than a question.)

Songs of Brood X cicadas in the Ohio River Valley

In the 80s, there was a telephone hotline, where the phone rang off the hook for days on end. And then, once the world wide web took off, there was a website where people could submit their sightings, then an email address, and finally, now, an app created by Kritsky and funded by Mount St. Joseph. Now in its third year of data collection, Cicada Safari has reached over 196,000 downloads, and its users have uploaded hundreds of thousands of photos and videos, each timestamped and geotagged. (Some app users are evangelists, too; when I was admiring cicadas at a park in Louisville, Kentucky, a stranger approached to encourage me to download it.) By mid-May, the app had amassed so much data that the servers were overloaded. Kritsky said he measured this by the time it took for the loading screen—a cicada flapping its wings—to disappear. The loading screen cicada, he said, had slowed to 14 wingbeats, so his team upgraded the one lone computer processing app submissions to a cluster of 64 networked CPUs.

The richness and volume of data Cicada Safari users submit is difficult to compare to, say, Marlatt’s maps. Marshall calls this “the opaque window of the past”—you don’t know exactly how previous researchers collected their data, and you can’t go back in time to get better data. Current researchers now know that some of the earliest cicada records conflated multiple broods; it just so happened that several emergences documented by cicada surveys happened to be years that 17-year and 13-year cicada broods coincided. (For instance, some Brood X sightings from 1868 and 1885 were actually 13-year brood XIX or XXIII cicadas.) Simon revised Marlatt’s maps in 1988 using newer observations from researchers (her own included), but even so, researchers take Marlatt’s maps with a grain of salt, especially when trying to determine population or distribution trends. In general, Cooley says, early maps tend to overestimate the historical range of cicadas, so “of course it’s going to look like they’re shrinking.” But according to Simon, even if that’s true, there’s still evidence of decline: “The distributions had definitely decreased, not surprisingly.”

To make the task of comparing cicada broods’ size and range even more complicated, some cicadas are “stragglers”: individuals that emerge off their brood’s usual cycle. Despite what their name suggests, most stragglers are actually early, usually by four years. Others are four years late, or off by a year in either direction. Because there is no known method to determine a cicada’s age, researchers have no way of knowing which brood a cicada is supposed to belong to. The periodical cicada literature is scattered with examples of potentially misidentified stragglers: The USDA’s 1932 data, for example, stated that Brood VI was the most widespread 17-year brood, but just one emergence later, the brood’s range, as described by entomologist Howard Deay appeared to have shrunk. Now, researchers believe Brood VI exists only in pockets of the Carolinas and Georgia. “The apparently changing distribution of brood VI and the scattered nature of many of its populations suggest that many records derive from misidentified stragglers,” Marshall wrote in a 2001 paper analyzing brood distributions.

Climate change might further exacerbate the straggler issue. While it’s not yet clear exactly how cicadas track the passage of time, researchers think they might count cycles based on information from their surroundings, and the tree roots they’re feeding off of. If that’s the case, extreme weather—an April cold snap, or an unusually warm winter—could throw off the count. “There are other possible explanations, but the link between climate change and widespread periodical cicada straggling events is a solid working hypothesis,” Cooley, Simon, and Marshall write on their cicada website. “If indeed unexpected emergences are related to climate change and are not simply a fluke, then other large-scale straggling emergences associated with other 17-year broods are to be expected.”

The existence of stragglers is natural, and it’s not yet clear how it will affect overall cicada populations. On one hand, some researchers theorize that “straggling” might be how we ended up with 13 year broods in the first place—cicada broods have speciated or expanded their ranges through these variations. Among Brood X cicadas, that might already be happening. In 2000—the year Neil Armstrong was on campus—Kritsky observed a large early emergence, and found that these stragglers continued on a 17-year trajectory, emerging again in 2017. That year, Brood X cicadas also emerged 4 years early in the DC area, and researchers are eager to see whether these early cicadas will come out again in 2034. That’s one benefit of Cicada Safari—with so many eyes and ears on the ground, researchers will be able to get much better records of stragglers. “It’s led to some really good discoveries, especially obscure discoveries,” says Cooley. App users have identified pockets of isolated cicadas in places the researchers hadn’t recorded them before. And so far, during the 2021 emergence, Cicada Safari has received reports of Brood X in South Carolina and Alabama, further south than their typical range.

But straggling could lead to extinction if cicadas don’t come out in adequately ample numbers. The abundance of cicadas is part of their overall life strategy, which biologists call predator satiation: There are simply so many individuals during an emergence that local predators—birds, fish, turtles, snakes, dogs, squirrels, and yes, even humans—can eat their fill and still leave plenty of individuals to carry on the next generation. But when stragglers emerge, they may not do so in sufficient numbers for any of them to survive. For example, Kritsky says some of those early-straggling Brood X cicadas from 2000 came out early again, in 2013—but they were quickly eaten. That’s such a common fate for stragglers that researchers have given them a name: shadow broods.

As populations of cicadas become more of a patchwork, as Kritsky describes, the same fate might befall on-time cicadas, too; their decreased density may not satiate predators, and each patch of cicadas will grow smaller and smaller until they’re all picked off. Below a certain threshold, says the UC Davis ecologist Yang, “they’ll blink out.”

 

Say the cicadas blink out. What, if anything, do we lose? How much can a single insect species—especially one with such a strange life cycle—matter to a local ecosystem?

As a young graduate student, that’s what Yang wanted to know. At the time, he and his colleagues were drawn to the idea of biological invasions: What happens when a novel species shows up outside its historical range and starts interacting with new species? This question was hard to test experimentally; studies that introduced invasive or exotic species were deemed unethical. But then, Yang heard about the 2002 emergence of Brood VIII cicadas, and he knew they would be the perfect study subject. “It’s a new species, in some ways, but it’s a native species, and part of that ecosystem,” he says. “When these periodical cicadas show up and haven’t been around for a long time, all the organisms in the community have to start interacting with this new potential resource or competitor.”

According to Yang, the first study he designed that summer was a “pie in the sky idea”: He wanted to know whether the mass of dead cicadas affected local soil and flora. “At the time, the conventional view was that insects were a pretty negligible part of the ecosystem,” he said, but he had a hunch that all those exoskeletons and dead cicadas must have some measurable effect. Yang marked out some plots in Pennsylvania’s Powder Mill Nature Reserve, then buried ion exchange resin beads—what he describes as “a tea bag full of tiny plastic beads”—in the soil. The beads, sometimes called “plant root simulators,” mimic the way plants absorb compounds like nitrate and ammonia from the soil. Then, he spread cicada carcasses across test plots to simulate the biomass of a typical cicada emergence.

For the next few summers, Yang was a full-time cicada chaser, establishing research sites wherever the next brood was set to emerge. “My truck kept breaking down and I’d be driving around on those old forest roads in Maryland, trying to find cicadas,” he said. In each place, he’d collect thousands of cicadas to be used as fertilizer in his study plots, so many that Yang felt compelled to add an acknowledgment to his dissertation thanking the twenty to thirty thousand cicadas that made his work possible. He went wherever the cicadas were: sometimes a pristine botanical garden in Virginia, sometimes the parking lot of a Kansas strip mall, or a Girl Scout camp. “It was always kind of comical,” he said. “Cicadas don’t seem to be picky.”

Finally, it was time to look at the results of his cicada fertilization. Yang was pleased to see that his hunch was confirmed; by the end of the 100-day experiment, cicada-fertilized plots had about twice as much nitrogen and four times the ammonium of his control plots. Next, he wanted to know whether that nutrient increase actually changed plant growth, so he moved on to fertilizing bellflowers with dead cicadas. The bellflowers, too, had a higher nitrogen content after being fertilized with cicadas, and produced larger seeds. Yang concluded that cicada emergences are important resource pulse: “infrequent, large-magnitude, and short-duration events of increased resource availability.” In other words, the huge influx of cicadas can be a boon for a local ecosystem. The handful of other studies exploring the idea of cicada emergences as resource pulses find that the influx of cicadas affect not only flora, but also fauna: Many bird populations grow during emergence years and immediately after, and mice populations experience a boom as well.

But this all only happens as long as there are enough cicadas to go around—enough to not only satiate predators but also to procreate and give rise to the next generation. Several researchers point to one spot in particular where the population seems to be circling the drain: Raccoon Grove Nature Preserve, just south of Chicago. In the 1950s, entomologist Henry Dybas and zoologist Dwight Davis recorded what Yang calls an “outrageously high density” of Brood XIII cicadas: 1.5 million individuals per acre, the highest ever recorded. But when Yang collected data there in 2007, he was disappointed. “There were hardly any,” he says.

The numbers at Raccoon Grove point to an obvious change, but there are other places he remembers differently, too. “I went back to Powder Mill in 2019 and the cicadas were there again—it was nice to see them,” he says, but the numbers were, like at Raccoon Grove, underwhelming. Ever the scientist, Yang immediately second-guesses himself; he’s not sure what to make of his own anecdote. “Is that because my memory of 2002 isn’t that good? It was the first time I’d seen them, so maybe I exaggerated them in my mind. Or is it true that the population is less dense than it used to be, a smaller population 17 years later?” Our memories are fallible; our perspectives—especially on what might constitute a “big” cicada emergence—might change over time. Kritsky likens it to going back to the house you grew up in, and feeling like the place is smaller than you remember, the ceilings lower. “The house didn’t change,” he says. “You did.”

 

Back at the cemetery, Kritsky and I finish up his first survey of the year and hop in his car, a Chevy Malibu with the license plate CICADA. As we drive back towards his office, I ask him about something that’s been on my mind. To me, it feels like cicada data will always be unsatisfyingly inconclusive. Even with thousands of citizen scientists on the ground, it’s impossible to track a brood’s full range, much less every single cicada; a definitive ruling on cicadas’ decline is elusive.

Kritsky says he’s gotten this question before. “I had people ask me a few years ago, why should Mt. St. Joe do this? Why are they willing to spend $60,000 on an app? Why do they give me the server space to do the app, to keep it going? Why is it we even care about the cicadas?”

Then, he tells me a story about a conference he spoke at a few years ago, which honored the work of Gregor Mendel using the lens of Pope Francis’s 2015 encyclical Laudato si’. The papal proclamation draws attention to climate change and biodiversity loss, the need for better research, and entreats the people of the world to “care for our common home.” Kritsky’s an avowed atheist, but I sense that his point is that it’s not just about the data itself; it’s about the effort behind the data, too. Every day, Kritsky gets emails with pictures of cicadas from citizen scientists, who may not have cared at all about these strange insects before seeing him on Kimmel or the local news. When I called one Cicada Safari user who was on the leaderboard for submissions, she told me she loathed cicadas in 2004, but after learning about them through the app, she was enamored. She could hardly wait, she said. I realized the same was true for me; the charisma of Magicicada turned my fear into fascination, and finally, respect.

Kritsky repeats my question: so, why do we care? And then he answers it: “A world without periodical cicadas is just not as nice of a home.”

Douglas Fox

Jane C. Hu

Jane C. Hu is an independent journalist living in Seattle. She’s a regular contributor to Slate’s Future Tense, and her work has appeared in publications like Undark, The Guardian, High Country News, WIRED, Smithsonian, National Geographic, The Atlantic, Science, and others. She teaches science writing at the University of Washington.

Christy Frank

Christy Frank

Christy Frank is a freelance conservation and documentary photographer, writer, and filmmaker based in the Great Lakes region. She is passionate about storytelling that intersects environmental and human conditions, science communication, habitat restoration, and species recovery efforts. Her work has appeared in Audubon, National Wildlife Federation, CBS News, PBS Nature, and other outlets.

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