This year, Wisconsin will see convergence of cicada species that happens every 2 centuries

Wisconsin and other states around the country are bracing to host trillions of visitors this summer in an event that’s even rarer than the solar eclipse that happened around much of North America on April 8. 

Two broods of cicadas — one that lives on a 13-year cycle and the other on a 17-year cycle — will emerge from the ground this year to breed.

Late spring and early summer in the forests of the eastern half of the U.S. have been eerily quiet for the past two years. In most years, long-lived periodical cicadas thrum through the region, but a quirk of timing means these insects have been sparse since 2021. This year, though, they’re roaring back.

That’s because 2024 will see two separate batches of periodical cicadas emerge en masse, spread across much of the eastern half of the U.S. These insects crawl out of the ground once every 13 or 17 years for a rush of mating and egg-laying until all the adults die, and the next generation is tucked underground until their own teenage years. It’s an unusual but ancient lifecycle that has become part of the fabric of Eastern U.S. forests. And it will be on full display this spring, with both a 13-year brood and a 17-year brood emerging across adjoining territories—a particularly rare occurrence.

“They don’t often coincide in time, but to have them coincide in time and space is even more unusual,” says John Lill, an insect ecologist at George Washington University. “That’s what’s happening this year that’s generating a lot of buzz—pun intended.”

Most of the periodical cicadas the U.S. will see this year belong to the Great Southern Brood, aka Brood XIX, a 13-year cohort that stretches across Missouri, Arkansas, southern Illinois, Tennessee, Alabama, Georgia, the Carolinas and surrounding states. The 17-year cicadas due this season belong to Brood XIII, or the Northern Illinois Brood.

These groups of cicadas hatched in 2011 and 2007, respectively, from eggs laid in tree branches. The newborn cicadas fell and burrowed into the ground surrounding their birth tree, then spent more than a decade underground, where they slowly bulked up by sipping on xylem sap. This fluid is mostly water and contains some minerals and other compounds. It moves from the tips of a tree’s roots toward the trunk and then upward. Now that the insects have matured, they will start to emerge when the surrounding soil reaches about 64 degrees Fahrenheit. This will likely start in the South as early as late April. Then the cicadas will begin their own weeks-long breeding binge before death.

Illinois will truly be rich in these insects because it marks the boundary between the two broods. “I’ve been looking forward to this for years,” says Catherine Dana, an entomologist and an affiliate at the Illinois Natural History Survey at the University of Illinois Urbana-Champaign. “We have two different broods emerging in the same state, and that’s a very rare thing.” The two broods’ territories don’t overlap much, but they do border each other. So while there won’t be any regions of unusually high density, scientists are looking forward to seeing whether the broods might manage to interbreed.

Brood interbreeding is surprisingly complicated because 13- and 17-year cicadas are different species, and each brood can include multiple species. All told, the U.S. is home to seven different species of periodical cicadas, all in the genus Magicicada—and this year, all seven will make an appearance at the brood boundary. “That’s pretty remarkable,” Lill says.

Although species of cicadas each look slightly different, their real distinction comes in the calls male insects make with ridged membranes on their abdomen. Each species in a brood makes a different set of songs, which females then recognize.

Of the 3,400 species of cicadas in the world, only nine species are known to have developed the strange habit of disappearing underground for years at a time and then emerging en masse simultaneously—and seven of them are in the U.S. During an emergence, it may feel like the cicadas are trying to take over the world, but the reality is far from it—they’re just seeking safety in numbers.

“The whole point of the gigantic co-emergence is that they are synchronously coming out and satiating their predators,” says Martha Weiss, an insect ecologist at Georgetown University.

“Because cicadas are hyperabundant, they are entirely undefended. They are not poisonous, they’re not spiny, they’re entirely palatable, they are slow flyers—they really are just sitting ducks. Their defense is coming out in the billions,” she adds. “Predators really just can’t possibly eat all of them.”

But predators sure can eat a lot of them—and they benefit tremendously from the sudden cicada banquet. Birds are particularly fond of munching on cicadas, but a range of mammals, reptiles and even fish snack on the insects as well. Birds eat so many cicadas that their usual prey, left mostly untouched, can flourish, Lill says—so much so that during emergence years, trees can suffer from higher-than-usual damage by caterpillars and other insects that birds usually keep under control.

And female cicadas also damage trees directly by slicing into twigs to lay their eggs. Although these two types of damage rarely kill trees, the effect is enough to reset the clocks of trees such as oaks, which typically undergo “mast years” in which they produce large batches of acorns every few years in synchrony. After accumulating damage during a cicada emergence, these trees produce lean harvests for two autumns in a row and then a feastlike burst of nuts two-and-a-half years after a cicada emergence, Lill says.

The relationship underscores how periodical cicadas have shaped the forests they live in despite spending most of their life underground, Lill says. Periodical cicadas “were here long before people were,” he says. “They have a really strange life cycle, but they’re an intrinsic part of these forest ecosystems that have been here for millions of years.”

And it will be an unusually long time before two cicada broods emerge simultaneously again—not until 2037, when the 13-year Brood XIX cicadas born this year and the 17-year Brood IX of North Carolina, Virginia and West Virginia both make an appearance. The delay makes this year’s cicada circus a spectacle not to be missed.

“Kids will remember this for their lifetime,” Dana says. “Maybe they will remember it as being disgusting and loud, but it’s also, in a way, magical.”