Billions of Cicadas Are Coming amid Rare Double Brood — See Where the Bugs Will Be This Spring (2024)

In Spring 2024, weeks after the April 8 total solar eclipse, two broods of periodical cicadas will emerge, and billions of bugs will begin to cover parts of the U.S.

The cicadas emerging are Brood XIII — a group of 17-year periodical cicadas — and Brood XIX — a group of 13-year periodical cicadas. This is the first time in 221 years that the two broods will be above ground at the same time, and the groups of bugs are set to overlap geographically, too.

Some are calling the upcoming double emergence a "cicada apocalypse," conjuring up visions of a world clogged with insects in every nook and cranny. PEOPLE talked to two bug experts about the emergence of the two cicada broods, who assured us that the result of the double emergence won't be a scene straight out of a science fiction film. In fact, the double emergence could become a fond "generational memory."

Read on to learn what Dr. Gene Kritsky — the professor emeritus of biology at Mount Saint Joseph University who literally wrote the book on 2024's double cicada emergence— and Steve Nicholls, an entomologist and wildlife filmmaker, have to share about the double cicada emergence this spring and where the bug broods will overlap.

Where will the two cicada broods emerge?

Brood XIX, also known as the "Great Southern Brood," is a "really big brood," says Nicholls, that covers much of the southeastern U.S. Brood XIX's estimated emergence areas are shown with red dots in the map above.

Brood XIII "is called the Northern Illinois brood, which, not surprisingly, is in northern Illinois and nearby areas and is a much smaller brood," says Nicholls. The map above shows Brood XIII's estimated emergence areas with blue dots.

When will the cicada broods emerge?

"We're expecting the periodical cicadas to start emerging in the last week of April at the southern end of their distribution, which is across Northern Louisiana, Northern Mississippi, Northern Alabama, and Georgia. That could happen as early as the last week of April into the first week of May," Dr. Gene Kritsky says of the 13-year cicadas in Brood XIX.

According to Nicholls and Dr. Kritsky, soil temperature determines when cicadas emerge. Once soil temperatures reach 64 degrees Fahrenheit, the bugs begin to emerge from the ground. This means the two broods of cicadas will not emerge all at once.

As spring progressively moves north and warms the soil, cicadas in those areas will start to emerge.

When you get to northern Illinois, the epicenter of Brood XIII, "you're looking at the last week of May" for emergence, says Dr. Kritsky. He adds that in 2007, the brood started to emerge on June 7.

"And the emergence, it's not like all or none; it takes two weeks for all the cicadas to come out in a given location," he adds.

Since cicadas live for about a month after they start to emerge and take about two weeks to emerge entirely in a given area, cicadas will be present in their emergence areas for about six weeks altogether.

Where will the two cicada broods overlap?

"There's been a lot of hype and concern about this overlap zone," Dr. Kritsky tells PEOPLE, adding, "I think people are expecting to see double the cicadas, a cicada apocalypse or Armageddon."

He assures that the reality of the overlap zone is far less dramatic, "It's a very narrow area. Moreover, it's at the extreme edge of both broods. And at the edges of the broods, that's where the numbers aren't as great."

Based on the estimated emergence area of each brood — detailed in the map above — Brood XIII and Brood XIX are most likely to overlap in central Illinois toward the state's border with Indiana.

"Springfield could be the cicada tourist center," Nicholls jokes about the overlap area, adding, "Where they do overlap, there's will be a lot of bug gossip."

"We don't know the exact distribution, so it is possible that a few areas will get a double emergence. But I think ultimately what'll happen is that you can drive for a lot further and see cicadas all the way," he adds.

What is a periodical cicada?

"There are 3,000 species of cicadas across the planet, but only a few of them are kind of periodical," says Nicholls, who recently consulted on A Real Bug's Life, the new Disney+ original series from National Geographic.

Periodical cicadas mature underground for long periods before emerging; depending on the species, this period could be 13 years, like brood XIX, or 17 years, like Brood XIII.

"There's one in Fiji that comes out every eight years. And one in India, called the World Cup Cicada, because every time it comes out every four years, at the same time as the soccer World Cup," the entomologist says.

"To summarize the life cycle, the adults mate and lay eggs. The female has a saw-like structure tip of her abdomen, which she uses to saw a little slit in a plant stem to put her eggs in. After the cicadas have gone, you can see the egg scars on all the branches. Those eggs hatch out, and then the nymphs, little tiny things, take the plunge," Nicholls adds.

The newly hatched nymphs "literally leaps off the tree down to the ground," he explains. "And then they dig themselves underground, and that's where they stay, in the case of the ones we are talking about, for either 13 years or 17 years."

Once periodical cicadas are fully grown, they sit close to the surface and wait for the soil to reach the right temperature.

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What is a cicada brood?

"A brood is like a year class," Dr. Kritsky explains, adding that entomologist Charles Marlatt devised the cicada terminology in 1893.

According to Dr. Kritsky, Marlatt decided, "Every 17-year cicada that comes out in 1893, we're going to call that Brood I. The 17-year cicada that comes out in 1894 is Brood II, and so on. For a 13-year cicada, if it came out in 1893, that was Brood XVIII, and so on. The first 17 numbers are reserved for 17-year cicadas. The next 13 numbers are for 13-year cicadas."

"By just saying Brood XIX, you know immediately that's a 13-year-old cicada," he adds.

Are double cicada emergences rare?

While Brood XIII and Brood XIX haven't emerged at the same time in 221 years, "double emergences do happen often," says Dr. Kritsky

"There are 12 distinct broods of 17-year cicadas and three distinct broods of 13-year cicadas. Twelve times three is 36. So, in 2021 years, it can happen more than 30 times. But what is unusual about this one is that there's a zone of overlap, of potential overlap. For example, when Brood IV emerged along with Brood XIX in 1998, they were hundreds of miles apart," he adds.

Do cicadas pose any dangers to humans?

"Cicadas do not spread disease. They don't bite humans. They're not a sign of filth. They don't have chewing mouth parts; they're not going to chew up your plants. The only damage they can do is when the female lays her eggs in the branches of trees; sometimes, those branches will break, and the leaves will turn brown. But for a mature tree, that's not a problem. It's like a natural pruning. And the flower set next year will be even bigger," Dr. Kritsky shares, calling the bugs "not a major pest at all."

According to Dr. Kritsky and Nicholls, cicadas are often boons, especially for other animals.

"When cicadas start flying around, they become food for all sorts of opportunistic predators: dogs, cats, birds, all sorts of birds, turtles, snakes, chipmunks. I've seen deer eat these things. And that's part of the cicada's survival mechanism. They basically overwhelm their potential predators with so much food that the predators get tired of eating them, and there are still millions left," Dr. Kritsky says.

When the billions of bugs start to die and leave their carcasses behind, the accumulations can rot and stink in the rising spring temperatures, but even then, the cicadas are doing good.

"You will never forget that smell. It's a scent memory. As these stinking carcasses start to decay, those nutrients go into the soil around trees, creating a nutrient cache for the tree and the cicadas. So they do a lot of good for the ecosystem," Dr. Kritsky adds.

He encourages people not to fear the cicadas—or to kill them with pesticides since they are not effective against the bugs—but to embrace the opportunity to see an amazing natural event.

"If you are lucky enough to have this in your backyard, get the kids, go out there, and watch this. It's like having David Attenborough special in your backyard. It creates a generational memory," he says.

He also encourages people to document their cicada sightings on Cicada Safari, an app Dr. Kritsky helped create to crowdsource cicada sightings and better understand the bugs.