A Wildlife Article from All-Creatures.org

A trillion cicadas will emerge in the next few weeks. This hasn’t happened since 1803

From Juanpablo Ramirez-Franco, Grist.org
May 2024

Brood XIX, the largest Cicada brood, and Brood XIII, among the densest of the broods, have spent the past 13 and 17 years respectively burrowing through the soils and feeding on the nutritious fluids from tree roots. Now they’re waiting for a deeply ingrained, instinctual clock to tell them to burrow out of the ground all at once... They'll be a little early this year, thanks to climate change.

Cicada - Ed Reschke / Getty Images

If you live in the Midwest or the Southeast, you know the cicadas are coming.

And if you live in Chicago, you know the Cicadalypse is coming.

Cicadas, winged buggy noisemakers whose relatives include leaf-hoppers and spittle bugs, come in two varieties: the annual cicadas who, sure enough, appear every year and the periodical cicadas, who appear in 13-year and 17-year cycles.

This year, however, those two periodical broods — known officially as Brood XIX, the Great Southern Brood and Brood XIII, the Northern Illinois Brood — will emerge at the same time, and in some parts of central Illinois, side-by-side.

The double-emergence hasn’t happened since 1803. For a little perspective, consider that in 1803 Chicago was not yet a city, just a fort built at the intersection of what is now Michigan Avenue and Wacker Drive.

The cicada emergence will span 16 states that range from Oklahoma to Virginia, and some cicadas have already started emerging in the South. It will probably start in the Midwest in a day or two. In certain parts of Illinois, scientists say the two broods will be close enough to hear each other singing, a noise level that can boom louder than a jet engine.

While much has been made of the noise level of all those chirping cicadas, some scientists are taking a closer look at the timing of their visit. Thanks to climate change, the cicadas are ahead of schedule.

Emergence depends on a key variable: soil temperature. Cicadas are touchy, and will only burst out of the ground once the soil temperatures about 6 inches deep reach around 64 degrees Fahrenheit.

“That’s the magic number,” said Floyd Shockley, an entomologist and collections manager at the Smithsonian National Museum of Natural History.

Stephanie Adams, a scientist at the Morton Arboretum in suburban Chicago, displays a cicada in her palm. Juanpablo Rameriz-Franco / Grist

Brood XIX, the largest brood, and Brood XIII, among the densest of the broods, have spent the past 13 and 17 years respectively burrowing through the soils and feeding on the nutritious fluids from tree roots. Now they’re waiting for a deeply ingrained, instinctual clock to tell them to burrow out of the ground all at once.

But that clock could be ticking faster these days.

“We’re on a gradually warming planet,” and the periodical cicadas know it, according to Shockley. He said the first cicadas to emerge this year crawled out back in February — which isn’t totally out of the norm. There are early birds every year, but this year he said there was an “extraordinarily high number” to come out prematurely.

“It’s happening earlier and earlier,” said Shockley. “And we think that it is totally related to the conditions locally being just right earlier and earlier because of climate change.”

The soil temperatures when cicadas will begin to emerge typically occur sometime in mid- to late-May, according to Scott Lincoln with the National Weather Service’s Chicago office. But, the average date when soil temperature would prompt the cicada emergence has been trending earlier over the last 30 years: approximately six days earlier in one Chicago suburb, and approximately 10 days earlier further northwest in DeKalb, Illinois.

According to scientists at the Morton Arboretum in suburban Chicago, it’s not just the cicada getting ahead of themselves. All kinds of species of trees, shrubs, and perennials bloomed unseasonably early this year. Maples, elms, and magnolia trees bloomed almost a month prematurely in the Chicago region.

There are close to 200 species of cicada in North America, only seven of which exhibit synchronized 13- and 17-year life cycles — otherwise known as periodical cicadas. These cicadas, the longest living of the species, have historically emerged in late spring or early summer, compared to the annual cicadas which come out every year near the end of the summer. The two never overlap. By the time the annual cicadas come out, the periodicals are long dead.

There are currently 15 periodic broods spaced across the eastern United States, 12 of which are synchronized to a 17-year life cycle and three that are synchronized to a 13-year cycle. Every brood contains a minimum of three or a maximum of four of cicada species — each species with its own signature tune.

For a brief several weeks, some residents of central Illinois will be able to hear all seven species of cicada in a single day, according to Shockley.

Some scientists, according to Stephanie Adams with the Morton Arboretum, believe that rare proximity between the two broods could allow species from the neighboring broods to court, mate, and potentially reproduce. “There is curiosity on whether they’re gonna hybridize and maybe produce a whole new species, so that is genuinely unknown,” she said.

A recent study found that the sheer number of cicadas droning around the many forests of the eastern United States will be a can’t-miss feeding frenzy for some 80 bird species. The short-lived bump in cicada calories isn’t just good for birds, it’s also a major boon for the caterpillars that will get a rare break from their predators.

At the Morton Arboretum in suburban Chicago, Rachel White, left, and Rachelle Frosch, on the ladder, swaddle a young tree in tulle to protect it from emerging cicadas. A female cicada can harm small trees and shrubs by cutting into the bark while depositing her eggs. Juanpablo Ramirez-Franco / Grist

All told: billions upon billions of cicadas will drone on for four to six weeks, but no one is getting hurt — just potentially irritated.

Cicadas don’t have stingers, they don’t bite, and they pose no real threat to humans. But the insects can damage small trees and shrubs as part of their life cycle. The damage is caused when the female starts laying her eggs: she will cut into the branches of small trees and shrubs to lay up to 600 eggs inside the bark.

The best way to protect vulnerable trees? Run to a fabric store and pick up the nearest bolt of tulle. The idea is to wrap the material typically used for ballet tutus around the tree like a lollipop. The hope is that the fine, lightweight mesh keeps the cicadas off and the sunlight in.

But if the tulle doesn’t make it in time, then it’ll take the eggs six to eight weeks to mature after being deposited into the small branches of young trees, during which time the tips of affected branches will turn brown: “It’s a natural pruning event,” said Shockley. If they survive, those same trees will be bushier and healthier the following year.

Eventually, the cicada nymphs will hatch, fall into the ground, burrow down, and start their 13- and 17-year cycles all over again.

“They’re a great barometer for the impact of humans on a species that was here before humans got here,” said Shockley. “And so watching those patterns tells us a lot about what impact we’re having on the environment.” 

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This coverage is made possible through a partnership between WBEZ and Grist, a nonprofit, environmental media organization.

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Posted on All-Creatures.org: May 27, 2024
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