Periodical Cicadas spend 17 years underground feeding on tree sap. Now, billions of cicada nymphs are once again preparing to emerge from the earth and take to the treetops of 15 states across the East Coast and Midwest. Ed Reschke/Getty Images
The last time periodical cicadas of Brood X emerged, blanketing sidewalks and lawns with their large shiny bodies and creating a deafening chorus, John Kerry was running for president, Barack Obama was an obscure state senator, and Donald Trump was praising Democrats on CNN.
Now, underfoot, billions of cicada nymphs are once again preparing to emerge from the earth and take to the treetops of 15 states across the East Coast and Midwest. The world has changed a lot since the last time these periodical cicadas emerged — and the cicadas themselves may be changing too, driven by climate change.
The periodical cicadas that will emerge this year are Brood X (pronounced 10) — one of the largest groups of periodical cicadas in the world.
Exactly when the creatures will crawl out of to ground and head for the treetops to mate depends on the weather and the ground temperature — the ground needs to be about 64 degrees, and a little rainfall can help trigger the emergence. Cicadas have already begun digging exit tunnels, preparing to climb out when the time is right.
"I'm actually a little anxious about it, like, when are they coming?" asks Ploi Swatdisuk. She was a senior in high school in Northern Virginia, the last time the periodical cicadas emerged, and does not have fond memories.
"It's just so gross," she says, recalling the squashed bodies of the large insects on her way to school. "I'm not really looking forward to it, and I don't know who could be except like maybe a wildlife biologist."
Indeed, people who study bugs are excited. "This is our Super Bowl, absolutely, for entomologists, we've been looking forward to this," says Michael Raupp, professor emeritus at the University of Maryland, also known as "the bug guy." It will be, he says, a "spectacular event."
The insects have been quietly waiting for 2021 to roll around for almost two decades.
"Remember, these are just teenagers and they've been underground for 17 years," Raupp says. "It's been a dismal existence. They want to come up and party."
Periodical cicadas are not to be confused with annual cicadas — the noisy creatures that create the late summer soundtrack in much of the country every year. Periodical cicadas live most of their lives underground, sucking sap from tree roots. Then, they emerge en masse. There are more than a dozen different cicada broods scattered across the eastern half of the U.S., all on different 17 or 13 year schedules.
To understand periodical cicadas' periodicity, and the strangely specific number of years they stay underground, Raupp says you have to consider cicadas' survival strategy. It's something called predator satiation.
"In other words, they're going to emerge synchronously in such massive numbers, they fill the bellies of every predator that wants to eat them," Raupp explains.
Even after predators' bellies are full, there are still many, many cicadas left to reproduce. But for this satiation strategy to work, the brood has to all emerge the same year — in overwhelming numbers. If just a few cicadas come out, on an off year, Raupp says, "They are eaten into oblivion."
As for the 17 years underground, Raupp explains that cicadas favor prime numbers. Emerging in prime number intervals helps different broods on different schedules avoid each other. Interbreeding could mess with those precisely timed schedules, leading to smaller numbers of cicadas emerging more often, making the satiation strategy ineffective.
Lately cicadas' schedules seem to be changing.
John Cooley has been studying cicadas since grad school in the '90s. He's now a professor at the University of Connecticut. Years ago he started a project mapping cicada broods. Whenever a brood starts emerging, Cooley and his colleagues spend weeks driving around with the windows down.
They listen for cicadas, and map what they hear. In recent years they've been hearing something unexpected — cicadas emerging years early, off schedule.
And, he says, it could be because of climate change.
"It is an absolutely intriguing possibility that as global climate change, it's throwing the cicadas off the cycle that they're supposed to be on and causing them to make mistakes," Cooley says.
Cooley says another possibility is that cicada behavior has remained the same, but humans are acting differently. Armed with smartphones and the internet, we may be reporting unusual cicada emergences more often than in the past.
Some early reports are already coming in, but the masses of cicadas aren't expected until mid-May.
For those who aren't excited about that prospect, Cooley has some advice — try to appreciate it for the unusual event it is.
"At this scale, there really isn't anywhere else on the planet where something like this happens," Cooley says.
In the midst of what's been a terrible pandemic year for most humans, the emergence of the periodical cicadas is a moment to pause, and marvel at nature. After all, who knows what life will be like next time Brood X comes out, in 2038.
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