Cicadas will soon die en masse in the Chicago and Illinois area, if they haven't already, but that doesn't mean the cicada invasion will simply end in 2024.

Residents still have to wait until the piles of dead cicadas have decayed and new eggs hatch and enter the soil, where they remain for another 13 to 17 years.

But how long does the decomposition take, does it produce a smell and what do you do with the dead cicadas?

Here's a breakdown.

What happens next?

Cicada-palooza has brought unprecedented numbers of insects to Illinois and other parts of the U.S. — and the same number that flew through the air will soon fall to the ground.

“What you saw was biblical,” said biologist Gene Kritsky, who has been hunting periodical cicadas for 50 years but was still amazed by the 3 to 5 million cicadas thronging a small patch of Ryerson Conservation Area north of Chicago. “I saw things this time that I've never seen before.”

Now the great emergence of the double periodic cicadas in 2024 – an event of a magnitude not seen since 1803 – may come to an abrupt end.

According to Kritsky, the event will likely last until the end of the month, but the end will be almost as dramatic as the emergence itself.

“It will be over in no time,” said Kritsky. “It was a lot of fun.”

Before all signs of the cicadas have disappeared, a phase of decomposition begins, which can result in an unpleasant odor for those who witness most of the emergence.

While several suburbs are reporting large numbers of cicadas, 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 across the United States. Those areas are unlikely to see much now that the hatching period is largely over.

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.

Some may already see dead cicadas on the ground.

What is that smell?

While what follows has plenty of benefits, the smell emanating from the piles of decaying insects may be off-putting.

Since the cicadas die in large numbers towards the end of the month, it will take some time for their bodies to decompose back into the soil.

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

What to do with the dead cicadas?

According to experts, the best solution is nothing at all. Those who can sit through the smell will actually benefit from it.

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

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.

What about cicada eggs?

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.

“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.

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.