Summertime Chi is marked by picturesque beach days, memorable street festivals and, every 17 years, swarms of cicadas.
With the return of the cicadas in full force and confused city dwellers wondering why they haven't been met with the forewarned “double-brood emergence,” Chicagoans are wondering how different this cicada encounter will be from years past and what's next for our noisy neighbors.
Time Out Chicago spoke with an insect expert to uncover what to expect and what us humans should really be worried about.
When will the cicadas be gone in Illinois?
The critters’ above-ground lifespan is only about two weeks, but portions of the brood emerge in rounds. The entire invasion is expected to last roughly four to six weeks, so expect some solace from the rhythmic screeching around the end of June.
Why are the cicadas coming out now?
There are about 150 cicada species in the United States and the Chicagoland area is lucky enough to only have three kinds that frequent our forestry: the upland, lowland and upland dwarf cicada.
These breeds, known as “periodicals,” synchronize their maturation and rise from the soil at the same time. Spending nearly all of their life below the surface, the cicadas feed on sap in tree roots, developing a palate for older and widely-branched trees.
Periodicals emerge every 13 or 17 years, and for Illinois, 2024 is the first time since 1803 that both 13-year and 17-year species will make their debut in the same year. It’s a rare phenomenon that only occurs every 221 years.
What will the cicadas do?
The cicadas remain burrowed roughly eight inches underground as they prepare to emerge. Once the outside temperature hits 64 degrees Fahrenheit during mid-May and early June, the conditions are ripe for the nymphs, or adolescent cicadas, to come out.
Once above ground, these nymphs perch atop plant stems of trees and shed their outer layer of skin. What’s left behind, the source of our bodily shivers and an entomophobe’s nightmares, are the nymph exoskeletons—and lots of them. Their goal is to reach the top of trees and begin their next major life milestone: mating.
What we perceive to be bombastic buzzing is really a mating call. With their species-specific harmonies, the male cicadas let out a melodic chorus of screeching in hopes of attracting the females. Swooned, the females flap their wings in response and get the good times going.
After they’re impregnated, the female cicadas use a tube-like organ called an ovipositor to place hundreds of eggs into the branches of trees. A few weeks later, the adult cicadas die, the egglings hatch and return back to the ground, where they’ll remain for the next 13 or 17 years.
Are there any risks?
Despite the widespread concern, there’s not too much for us humans to worry about, according to Dr. Diego de Santana Souza, a postdoctoral researcher in insects at the Field Museum.
“They’re not pests—they don’t destroy trees or feed on agriculture,” Dr. Souza said. “If you see them in your garden or backyard, they are just trying to climb as high as they can on tall trees.”
The cicadas are actually quite beneficial for the trees, Dr. Souza explains. Feeding on the sap within the tree's roots allows for necessary aeration, and depositing eggs into the branches encourages branched growth for the tree, providing support against strong winds.
As many notice the double brood of 13- and 17-year species appearing, the former will mostly affect Southern Illinois with a little overlap in places near central Illinois, like Champaign-Urbana. This year’s brood is expected to follow the same map as it has in past years, according to Dr. Souza.
Because many cicadas take up residence in trees, the most at-risk party would be young, freshly-planted saplings. The insects prefer large, older trees, so it’s rare for them to move into saplings, but concerned arborists can protect saplings with chicken wire or netting.
The only real annoyance the periodicals dispense is noise. Their screeching, mating call can reach up to 90 decibels (as loud as an electric power tool). With hundreds joining in at once, the choral production can be a bit overwhelming.
Otherwise, the remaining exoskeletons and carcasses left behind during the entire process could be treated like dead leaves in the autumn.
“Birds will eat them and they’ll decompose into the soil,” Dr. Souza said. “It’s probably best to just sweep them to the side if they’re covering a walkway or courtyard.”
Dogs, cats and even the bravest humans can eat the cicadas as well. For those tempted, places like LaBagh Woods or the North Branch Forest Preserve are the best places in the city to catch the broods.
Even though myths of an insect invasion will certainly pick up steam and novelty T-shirts will be sold, Chicagoans can rest assured that it’s business as usual for cicadas this summer.
What's next?
With millions of adult cicada carcasses being left behind, scientists warn of the next nuisance in the historic natural phenomenon: the smell. As so many cicadas decompose, unfortunate passersby may encounter the unpleasant smell of what experts say is natural decomposition. The stench is not expected to last long, however, and the remaining carcasses can be used to enrich compost bins or as soil fertilizer.
Interested entomophiles can get their lawn chairs and binoculars out in mid-July for the the egg hatchings. Six to 10 weeks after the eggs are laid, the hatchlings fall to the ground and re-enter the soil, restarting the years-long maturation process all over again. Lighting conditions may need to be perfect to catch a glimpse of the nymphs homecoming, but keep an eye out for thousands of the tiny insects falling out of tress.