'A 4 Week Bender:' A Million Cicadas Coming to Downstate Illinois

ILLINOIS — For many, it's not an Illinois summer without the rhythmic hum of cicadas. The annual guests pop out of the ground to eat, lay eggs and find a mate to spend the next three seasons with. In a few months, however, some downstate counties will recognize a note in the summer symphony that hasn't been heard in almost two decades.

The cicada group known as Brood X is emerging in five Illinois counties — Edgar, Clark, Crawford, Vermilion and Champaign, according to a cicada mapping site from the University of Connecticut. The group is also known as the Great Eastern Brood, and contrary to its numeral only emerges once every 17 years.

Northern parts of Illinois like Chicago and the surrounding areas won't see nearly as many cicadas until 2024, when Brood XIII makes an appearance.

"Cicadas are amazing because they have a crazy time-keeping mechanism to synch their emergences," said Robin DeLaPeña, an insect collections digitization specialist at the Field Museum in Chicago.

The cicadas that appear every 13 or 17 years are called periodicals, and are a different type than the annual cicadas many have grown accustomed to. While periodical cicadas aren't that loud individually, the billions of others in their posse add up to make quite some noise.

According to DeLaPeña, cicadas emerge only once the soil temperature reaches a balmy 64 to 68 degrees. Their inner clock allows broods to emerge at almost exactly the same time, but as North America sees worryingly hotter summers that warm up the soil, some stragglers from larger broods are emerging far too early.

"In 2020, five extra states that should not have had 17-year brood emergence were emerging," DeLaPeña said. "The main concern is if this kind of behavior starts to be more persistent, scientists will have a hard time tracking and telling the numbers from the 13-year brood, and you might find those populations will split off."

For now, stragglers don't pose a threat to cicadas, especially as citizen scientists help researchers track and identify the species from across the country. There are even phone apps like iNaturalist to document any bug-eyed creature you may see.

As news of murder hornets and giant beetles graced headlines around the world the past year, DeLaPeña hopes people don't feel fear towards cicadas, who are an important food source for some predators and even aerate the soil when they burrow out of the ground.

It may be loud and a little crunchy during summer walks in Illinois, but it only takes the Great Eastern Brood four to six weeks to do their business before they're eight inches under the soil again.

"People should be awestruck but not fearful," said DeLaPeña. "They're noisy as hell but nothing to worry about."