What you need to know about the historic cicada emergence

Across the Eastern U.S., trillions of flying, buzzing cicadas are struggling out of the ground and heading for the trees — part of the biggest congregation of the insects to emerge since 1803.

This historic emergence is happening from the Gulf Coast to Virginia, and from Illinois to the Atlantic.

It represents a loud racket for human neighbors, a hungry threat to local trees, a welcome reprieve to moths and butterflies and — perhaps most significantly — a sudden pulse of protein that can reshape forest ecosystems now waking up from winter.

If you live east of the Mississippi and south of the Mason-Dixon line, here’s what to know about the buzzing outside the windows.

What’s with the buzzing?

It’s the sound of millions of male cicadas making their mating calls — which should last, once it begins, for about a month and a half.

If the males’ songs are successful in attracting a mate, she will lay eggs in tree branches. The eggs then fall to the ground, where cicada nymphs will hatch and burrow into the earth, where they will eat tree sap for the next 13 to 17 years — until they emerge to start the process again.  

Why is this year’s emergence different?

Because cicadas generally emerge in either 13- or 17-year cycles — and this year those cycles overlap. 

For context in how rarely that happens, the last time the two coincided, Missouri — one of the hosts to one of the broods now emerging — had only months prior been bought by the new U.S. government from the empire of France.

Why those particular cycles?

No one knows — and 13- or 17-year cicadas often give birth on the opposite schedule. 

That said, there are a fair number of “stragglers” that emerge between one and four years before (or after) the main brood.  

OK, but why do cicadas emerge so infrequently?

It’s a numbers game, says Chris Simon, a research scientist in the school of Ecology and Evolutionary Biology at the University of Connecticut.

It’s a hard life for a cicada: everything eats them. When they’re tiny and underground, they are torn apart by ants and other invertebrates; as they get bigger, they become nutrient-dense snacks for burrowing mammals like shrews and moles. 

“And then, when they come out of the ground, they are food, of course, for everything above ground, like small mammals, birds, turtles, snakes, and humans,” Simon said.

But when a million and a half cicadas emerge per acre, “they get protection from safety in numbers,” she added.

Not all cicadas do this — there are nonperiodic cicadas as well as periodic ones — and cicadas, Simon noted, also aren’t the only creatures that do it. “There’s various plants and other animals that do this to try to swamp predators,” she said.

This strategy of self-protection for the species involves a lot of sacrifice for its individual members. 

By force of numbers, cicadas “effectively satiate their predators,” Louie Yang, an entomologist at the University of California Davis, told Vox a few years ago, when the famous Brood X emerged.

What are the impacts of the cicada emergence?

A bonanza for birds, as well as basically everything in the ecosystem that likes live prey. 

It's also, a welcome reprieve for everything that would otherwise be preyed upon — and a knock-on increase in the impacts caused by those animals, which will survive to eat more plants than they otherwise would.

That’s the conclusion of a paper published last October in Science, which found that more than 80 bird species switched from hunting their general prey to focus on cicadas — a nutrient pulse that boosts their offspring that year.

All told, "cicada emergences can completely rewire a food web," study coauthor Grace Soltistold the BBC. 

"For predators, these emergences are a huge boom in resources. It's basically like an all-you-can-eat buffet for the hungry predator."

This change in predator focus, in turn, allows caterpillar populations to double, and to lay more eggs in oak trees — which a 2022 paper in The American Naturalist found could depress the production of acorns for a couple of years after the brood’s emergence.

Does that make the cicadas bad news for oaks? It’s more complicated than that: The increased numbers of consumed cicadas mean similarly heightened amounts of nutrient-dense bird and animal poop deposited on the roots of trees, which ultimately “enhances oak reproduction,” the paper found.

When and where can we expect them?

The timing is simple, if variable: whenever soil temperatures hit 64 degrees about 8 inches down.

The geography is a bit more complicated. The 13-year brood — Brood 19 — will come out in the Southeast and Gulf Coast, popping up in Tennessee, Kentucky, Missouri, Arkansas, Georgia, Mississippi, the Carolinas and Virginia.

The 17-year brood — Brood 13 — will mostly come out in Illinois and Iowa.

“As far as we know, they don’t overlap,” Simon said — although she cautioned that discovering this wasn’t easy, because the two broods are functionally “identical in song and appearance.”

“We only know that they don’t overlap because we have mapped [each brood] in other years and other generations, where they came out by themselves.”

Is climate change impacting this process?

Continually, and for millions of years, according to the University of Connecticut. 

In the biggest picture, periodic cicadas are far older than the current geography of the United States, which was shaped by repeated expansions and melting of glaciers over the past 740,000 years.

This means that cicadas have survived — and their evolution has been shaped by — changes on the landscape that far outstrip any near-term changes caused by human burning of fossil fuels.

But over the short term, the UConn experts expect that the rise in average temperatures will push cicada emergence earlier as it pushes spring earlier.

“If the growing season is longer, they can reach maturity faster,” Simon of UConn said.

Another impact comes from increased climate variability — weird year-on-year fluctuations from the norm — which will disrupt the cues cicadas rely on to time their emergences.

At the extreme level, that could lead the insects to abandon the periodic strategy entirely. But also, if “extreme climatic conditions reliably and consistently induce straggler emergences of sufficient density to satiate predators, then permanent life cycle switches could occur,” according to a UConn fact sheet.

But far more significant than human-caused atmospheric climate change is the human-driven change in land use, Simon said.

“We convert the landscape, we remove their trees, we pave over their burrows underground. And because of that, there’s a lot fewer areas where periodical cicadas come out now than in the past,” she said.

Climate change, she noted, isn’t what decimated cicadas in her home region of New England: development did.

In the time since the last joint emergence of Broods 13 and 19, the forests of New England “were almost entirely removed, with only three rows in between fields and maybe along streams there will be trees left or up in mountains. And so, the cicadas would be wiped out wherever the trees are removed, especially when they’re completely removed for agriculture.” 

The result, she said, was that the size of the “northeastern broods are really dramatically decreasing. So, humans are really the biggest problem with the cicadas.”