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Have You Heard the Buzz? It's Cicada Season

You may have heard the hype by now. This year will be the year of the cicada spring.


A periodical cicada on a tree branch.
A periodical cicada on a tree branch. (Photo via Shutterstock)

You may wonder what all the cicada buzz is about. You might think, "I see and hear cicadas every summer. What is the big deal?”

Most often, the cicadas we see in our area are annual cicadas. These bugs have a life cycle that lasts between two and five years. Annual cicadas do not emerge all at once, and they have overlapping geographic ranges. Because of these factors, some of these cicadas will emerge in our area every year. 

This is the big deal!

A periodical cicada (left) and an annual cicada. (Photos via Shutterstock)

The periodical cicada brood we will experience in Northern Illinois is called Brood XIII (13). It emerges only once every 17 years. There is another brood in southern Illinois that will also emerge in 2024. It is called cicada Brood XIX (19), and it emerges every 13 years. 

Unlike the annual cicadas, these periodical broods emerge all at once and all in one area. 

Double, but not trouble

There are 15 active periodical cicada broods across the United States that emerge every 13 years or 17 years. Each of these periodical cicada broods has a unique geographic boundary. 


Words to know

Aerate: To introduce air into a material.

Annual: Occurring every year.

Fertilize: To make soil more fertile.

Geographic: Related to geography or the physical features of a place. 

Molt: To shed old skin, feathers, hair or exoskeletons.

Periodical: Occurring at regular intervals.

Resilient: Able to withstand or recover from difficult conditions.


In 2024, Illinois will experience both the 17-year and 13-year cicadas. This has not happened since 1803, when Thomas Jefferson was the president of the United States. That's 221 years ago! These cicadas will not emerge together again in Illinois until 2245, 221 years from now. 

What is the significance of the number 221?  Math fact: 221 is the least common multiple of the numbers 17 and 13! 

Though the state of Illinois will experience two broods of cicadas emerging this spring, only six counties in Illinois will encounter an overlap of both broods. Will County is not one of them. You would have to drive about an hour and a half south to find a county with an overlap of broods this spring. 

Life cycle

A periodical cicada emerging from underground.
A periodical cicada emerging from underground. (Photo via Shutterstock)

Once upon a time, 17 years ago, way back in the year 2007, trillions of rice-shaped eggs were laid in tree branches all across Will County by 17-year periodical cicadas. Six to 10 weeks later, tiny cicadas emerged from their eggs and fell to the ground. These young, pale hatchings, called nymphs, burrowed into the ground near the tree they fell from. 

They tunneled underground, where they spent 17 years. While down there, they sipped sap from tree roots. The nymphs slowly grew and slowly got stronger. As nearly all other insects do, cicadas shed, or molt, their exoskeletons as they grow. Over its lifetime, a cicada will molt five times. 

Back to the present day, spring 2024. When the temperature of the soil reaches 64 degrees at a depth of 8 inches underground, these nymphs who haven't seen the light of day since 2007 will begin to crawl up and eventually emerge from the soil. They will molt one last time, shedding a hard exoskeleton. 

These exoskeletons will be left clinging to trees and other structures in the area. See if you can find any exoskeletons where you live. Where do you find most of them? After shedding their exoskeleton, cicadas will live for four to six weeks above ground.

How do they know when 17 years have passed?

Cicadas communicate with trees!

Scientists don't exactly know how, but one theory is that cicadas can tell when to emerge by using the tree's annual cycle. Throughout the year, tree sap differs in amount and taste. These changes signal seasonal experiences: growing; producing buds in the spring; and shedding leaves in the fall. While underground, cicadas eat sap and gather clues from the trees that reveal the rhythm of the year.

Another theory is that cicadas have an internal clock that allows them to sense the passage of time — even underground! Humans have a 24-hour internal clock that is aligned to the cycle of day and night. How do you know when it is time to eat, go to bed at night or wake up in the morning? Your internal clock reminds you. 

Are you worried?

A cicada emergence of this scale may be something you have never experienced before. Being worried about something new is completely normal. Here are some things people may be uneasy about regarding the cicada emergence.

  • Diet: Cicadas only feed on plant-based liquids. They do not consume solid material. Cicada larvae suck sap from tree roots during their years underground. As adults, they suck liquids from woody shrubs and trees. 

  • Noise: Cicadas will be making quite the racket this spring. They make noise to communicate with each other, find a mate and even scare off potential predators. Even though cicadas are the world’s loudest insect, their chirping, buzzing sound will be about as loud as a lawnmower. 

  • Harmless: Cicadas don't bite. Cicadas don't sting. Cicadas are harmless to people and pets. 

Cicadas are beneficial!

A cicada on a blade of grass with two cicada exoskeletons on the other side.
A cicada and two cicada exoskeletons. (Photo via Shutterstock)

Cicadas are important for many reasons.

They prune mature trees. Some branches may fall to the ground after adult cicadas lay their eggs under the tree bark. 

Cicadas help aerate soil. Crawling around underground for 17 years, these cicadas make many tiny tunnels through the dirt. This helps tree roots grow and spread more freely. 

Cicadas fertilize. Adult cicadas live for only four to six weeks. At the end of their lives, their dead bodies serve another purpose. As they break down and decompose, the nutrients in their bodies become an important source of nitrogen for trees. 

They're great for the birds! Cicadas are an important part of the food chain and serve as a nutritious food source for humans and animals. Certain plants and animals have what we call a "mast year." This is when a species produces so many seeds or offspring that their predators could not possibly eat them all. This helps cicadas be resilient against predation. Even though many are eaten, there are many more that will survive long enough to mate and lay eggs. 

You can help future generations of cicadas

Because cicadas survive through masting (emerging in the billions), they are successful in the adult stage of their life. In their larval state, they are susceptible to harmful chemicals. Avoiding pesticides and chemicals on our lawns is one way to help protect these bugs that spend 17 or 13 years of their lives underground. 

Embrace this rare occurrence

Think about it. You won't get to experience periodical cicada Brood XIII for another 17 years! How old will you be for the next cicada emergence in Will County? Add 17 to your current age. Keep going and add 17 to that age. Depending on when you were born and where you live, you may only experience an emergence like this five times in your life! 

So this cicada season, do your best to coexist with these periodical pals and embrace this unique experience.


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