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The 2024 Illinois cicada outbreak isn't over yet. Here's what's next – NBC Chicago

Seeing a lot of dead cicadas? You're not alone, but that may not mean the outbreak is ending in Illinois.

This could mean that the cicadas are entering a new phase of their development: the mating phase.

Experts had explained that the cicadas would continue to emerge from the ground until the end of May/beginning of June, but that it would then take several days before they began their mating calls.

While cicadas have already been spotted in large numbers in parts of the region, a shift is being reported in some suburbs.

Dr. Gene Kritsky, dean of behavioral and physical sciences at Mount St. Joseph University in Cincinnati, who tracks cicadas' emergences throughout the United States and especially in Illinois, noted in late May that while the number of cicadas emerging from the ground will decrease at that time, that does not mean the end of the noise or sightings. Cicadas must continue to live out their life cycle above ground.

“The adult birds continue to sing loudly until mid-June, but their numbers decrease towards the end of June,” said Kritsky.

He noted that although emergence was slowing down, “the song was still getting louder,” indicating that the mating phase was largely underway.

When the insects first emerge, they actually remain silent for a while. According to Kritsky, it takes five days for a cicada to start singing after it emerges from the ground.

Since the insects only have a few weeks to live after hatching, they reproduce quickly.

Male cicadas make a loud noise when they run to attract mates before their life cycle ends.

According to the National Museum of Natural History, adult cicadas only have about three to four weeks to live after they emerge from the ground.

After mating, male cicadas complete their life cycle, while female cicadas drill slits into the branches of trees and lay eggs.

Some males die shortly after reproduction, but most do not “die immediately upon mating” and live for a short time longer.

“The eggs hatch six to seven weeks later, the nymphs fall to the ground and sink into the soil, and the cycle begins again,” the Natural History Museum said.

While the emergence in Illinois and the Chicago area lasted several weeks, the same will be true for the mating season.

John Cooley, an entomology professor at the University of Connecticut who is affectionately called “Doctor Cicada,” said those who see insects in pairs are about halfway through hatching.

While some may already see dead cicadas on the ground, for others the mating season may just be beginning.

In any case, residents do not need to be afraid of dead cicadas, says the expert.

Similar to their early lives, dead cicadas are actually beneficial to the environment.

“The dead adult insects fall back to the ground and help fertilize the soil. You can even add dead cicadas to your compost pile. It's a great example of the natural cycle of life,” says the Nature Conservancy.

Because cicadas die in large numbers toward the end of the month, it takes several weeks for their bodies to decompose back into the soil.

“They are free fertilizer for the trees,” Kritsky said.

The decomposition process may produce a rancid smell, but Kritsky said it will be short-lived and those who persevere will benefit.

Depending on the weather, the complete decomposition process could take several weeks, according to Kritsky, but the stench will stop sooner, he said.

While large numbers of cicadas are being reported in several suburbs, some parts of the region are seeing almost no cicadas, particularly in the northwest suburbs and Chicago itself, according to a map of cicada sightings in the United States. Those areas are unlikely to see much now that the hatching period is likely over.

The historic emergence in 2024 will see two broods of cicadas hatch simultaneously—Brood XIII and Brood XIX. These two broods of 13-year and 17-year cicadas have not hatched together in over 220 years. While much of Illinois saw only one brood hatch, a small part of central Illinois may have seen both broods.

Those who experienced large numbers of cicadas during this occurrence may have another opportunity to witness the historic cicada circus this summer.

Then the eggs begin to hatch in mid-July.

Hatching occurs six to 10 weeks after the eggs are laid, and while it's rare to see this moment, Kritsky said it can be observed in the Chicago area under the right conditions.

“When the sun is at the right angle, people have actually seen the nymphs fall to the ground,” Kritsky said, noting that the sun must be behind the tree where the eggs hatch “to illuminate them as they fall.”

In areas of heavy infestation, there could be up to 40,000 eggs lying dormant in trees, he added.

Anna Harden

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