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The Buzz

Sounds of Summer: 17-Year Cicadas Emerging, Making Presence Known




A periodical cicada. (Photo by Suzy Lyttle)

Cicadas are emerging in many areas of Will County right now, but the sound display they put on this summer is just a warm up to the main act, which won't be for a few years yet.

The cicadas people are seeing now are periodical cicadas, the bugs that are well-known for emerging from underground every 17 years and making their presence known with their loud buzzing sound. The ones emerging this year are a subbrood of the northern Illinois brood of cicadas, according to the University of Illinois Extension.

Both the 2020 subbrood and the main brood, which will emerge in 2024, are periodical cicadas that follow the 17-year life cycle. These bugs have been underground for 17 years, and now they are emerging and climbing into trees, where they will shed their exoskeletons. Once shed, their wings will be functional, and they'll begin looking for mates to start the life cycle all over again. 

All the time underground isn't spent in dormancy. The cicadas remain active, tunneling through the soil and feeding on roots from plants and trees. While their presence isn't noticeable while living underground, that changes in a big — and loud — way once they emerge.

That loud buzzing sound we associate with cicadas is an important part of their life cycle, because it is how the males attract female mates, according to National Geographic. And while the buzz of cicadas may just sound like a big racket to you, each species of cicada has its own call, and the insects can differentiate between them.

If you've ever said to yourself that the buzzing of cicadas sounds louder than a freight train, you wouldn't be that far from the truth. Some cicada species create buzzing sounds of more than 100 decibels, which is louder than an approaching subway train, National Geographic reports. The buzzing of cicadas can sometimes be heard more than a mile and a half away.

So how do small insects create such a big racket? The males have an organ called a tymbal that produces sound. The tymbal has a series of ribs that can buckle onto one another when the cicada flexes its muscles, the Peggy Notebaert Nature Museum reports. As each rib buckles, it creates a clicking noise, and the combined effect of the clicks is the buzzing sound we are all too familiar with. 

These periodical cicadas are one of two kinds of the insect that live in Illinois. Later this summer people also may see dog day cicadas, also called annual cicadas. Like their periodical counterparts, dog day cicadas also have life cycles that last multiple years — typically between two to eight years depending on the particular species — but their life cycles are not synchronized, so some emerge each year rather than all in the same year, making their arrival less noticeable. Dog day cicadas typically emerge from underground between July and September, according to the Morton Arboretum.

 

While annual cicadas are found all over the world, the periodical cicadas we are seeing now are unique to parts of the United States, National Geographic reports. These cicadas emerge and make their presence known only in parts of the eastern and central United States. While the periodical cicadas in northern Illinois emerge every 17 years, in some other places, including southern Illinois, they emerge every 13 years.

The varied life cycles aren't the only difference between periodical and dog day cicadas. They look different too. The dog day cicadas we see every year are green or black in color, and they have black eyes and transparent wings, according to the Morton Arboretum. Periodical cicadas have black bodies with orange wings and red eyes. Dog day cicadas also have bigger wings, typically about twice as long as the periodical cicadas.

If you're enjoying the display put on by this year's cicadas, the 2024 emergence could be a real show-stopper. That brood has a reputation for being the largest emergence anywhere, according to the University of Illinois Extension. The brood last emerged to much fanfare in 2007. In their emergence before that, in 1990, there were reports of people in the Chicago area having to shovel sidewalks of dead cicadas because they had piled up in such large quantities. 

Cicadas are often mistakenly referred to as locusts, but the terms are not interchangeable. Locusts are actually a type of grasshopper, while cicadas are unrelated to grasshoppers. Both locusts and cicadas do emerge in masses, but cicadas are not typically destructive, while locusts can eat all of the vegetation in their path, National Geographic reports. 

Cicadas don't eat plant matter as locusts do. They drink the sap from tree branches, limbs and roots. The adult cicadas — the ones that emerge from underground — live only four to six weeks, which limits their ability to cause destruction of plant matter, according to National Geographic. 

Among their environmental benefits, cicadas serve as a perennial food source for their many predators and the nymphs help to aerate the soil.

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