2 cicada broods are popping up together for the first time in 221 years — and they'll meet in Illinois

• Two broods of periodical cicadas are emerging simultaneously for the first time in 221 years.
• Broods XIII and XIX overlap in a small portion of Illinois, around Chicago.

2024 is the year of the cicadapocalypse.

That's because two broods of periodical cicadas — Broods XIII and XIX — will emerge from their underground lairs simultaneously for the first time in 221 years.

The last time the two broods teamed up, Lewis and Clark began their trek through territories recently acquired through the Louisiana Purchase, the US Supreme Court heard the landmark Marbury v. Madison case, and Thomas Jefferson was president.

Hype over the red-eyed insects has reached social media, where commenters are both dismayed and excited about prospective encounters with the dual cicada swarms.

"Which sign of the apocalypse are we on again?" one user on Instagram quipped.

"Leap year, cicadas, AND an election year? Idk if I can do it," one commenter on Instagram said.

Fortunately for those preparing to spend the spring in their basement, the two broods of periodical cicadas will not overlap — much.

Brood XIX will predominantly appear in southern states, while Brood XIII will appear in a small section of the Midwest — mainly Illinois.

One portion of Illinois will see an overlap. That's where cicada hunter Gene Kritsky, with his wife Jessee Smith, will be heading this year — along with many other cicada sites — to map out their appearances.

"I've been doing cicada mapping since 1976. I'm that old," Kritsky told Business Insider. "I'm going up into the Chicago region — I'll be there the first weekend in June — where I'll be lecturing and doing some hikes at the Lake County preserve area."

Kritsky, an author, professor at Mount St. Joseph University, and creator of Cicada Safari, an app that crowdsources cicada photos for scientific research, is excited to see cicadas again this year after last year's stragglers. He's very aware, however, of how polarizing the insect can be, both on and offline.

That's because they show up in thousands, make a lot of noise, and their crushed remains can even be a hazard to drivers by making roads slippery. Sometimes, they can harm young trees by attempting to lay their eggs in them.

However, cicadas are harmless and don't hurt people or animals.

"I've helped people plan vacations to where the cicadas are emerging," Kritsky said. "I've helped people plan vacations to be outside of where they're emerging. So there's both extremes on that."

Unlike annual cicadas, periodical cicadas spend years in their underground rooms like brooding teenagers (is that why they're called broods?) in 13 or 17-year cycles. In the case of the next two emerging broods, Brood XIII emerges every 17 years, while Brood XIX emerges every 13 years.

There are 15 broods in the US — 12 are 17-year broods, and three are 13-year broods. Kritsky said this means there have been other instances of two broods concurrently appearing in more recent history.

"In 1998, we had a 17-year brood come out with a 13-year brood," Kritsky said. "So this happens. It happened probably 12 times, at least, in the last 200 years."

That doesn't mean, however, that the periodical cicadas — which emerge in the millions — aren't a sight to see.

The life of a periodical cicada

Periodical cicadas, a red-eyed insect with a black body and orange rings, spend most of their life just inches below the dirt, beneath trees. It gets a bit cold at that depth, around 56 degrees Fahrenheit, so they don't move around much. The cicada nymphs tunnel around and live off of the sap of tree roots. Kritsky told BI that many live near parks and cemeteries in suburban areas because they are drawn to "mature trees, in full sun, with low vegetation."

This is their life for 13 to 17 years until it is time to reproduce. Scientists don't know exactly how they determine how many years have passed, but evidence shows that they keep track of seasons by detecting the flow of sap in the trees.

When the time comes, they emerge in late spring, when soil temperatures reach about 65 degrees. This happens at different times in different locations between late April and early June. Depending on temperatures, Kritsky said Brood XIII could appear in early June or late May. Brood XIX, also known as the Great Southern Brood, could appear as early as April.

The cicadas usually first appear at night. Males will make their way out for the first couple of days, climbing up trees, and females will later follow. The first days of freedom are about shedding their old exoskeleton and hardening their new exoskeleton to become fully grown adults. Then it's time to mate.

To attract a mate, male cicadas use an organ in their body that creates a sound similar to a shrieking buzz. This may be what people recognize most about cicadas because they can get loud — like running lawnmower loud.

If a female is into the call, they mate. The female then searches for trees in brighter areas, locates tiny twigs at the end of the branches, cuts into them, and lays between 400-600 eggs. If they run out of room on one twig, they'll fly to another, Kritsky said.

Once they complete their mission, adult cicadas soon die. In about six weeks, the eggs hatch from the trees, fall to the ground, and burrow into the earth to start the cycle again.

Crowdsourcing has changed the cicada game

Before Cicada Safari's existence, Kritsky said the highest number of records on cicadas was about 8,000 records of cicada locations. His research teams have received over half a million records since 2019, thanks to the thousands of cicada enthusiasts submitting photos. Kritsky said it's helped cicada scientists understand the distribution of periodical cicadas more precisely.

"We found records from areas where cicadas never got reported before, not because they weren't there, but no one knew who to report it to," Kritsky said.

The app has also helped researchers spot new patterns of emergence. Smaller swaths of periodical cicadas normally emerge four years earlier in a phenomenon that scientists are still trying to figure out. More recently, however, scientists have noticed cicadas emerging one year earlier.

In 2023, researchers like Kritsky were able to record these patterns — which may point to climate change-induced shifts — thanks to citizen scientists' observations.

But more than that, the app, Kritsky said, has encouraged people to connect with family and friends over cicadas.

"You can mark your life by cicada emergences that you've remembered," Kritsky said.