What do cicadas sound like, and why are they so loud?

CHICAGO (CBS) -- The periodical cicada broods are coming – and while harmless, they're famously quite noisy and loud.

The noise will be hard to miss. But it won't all even be the same noise – as there are several different species of cicadas coming that each have a distinct song, or screech.

There are two groups of periodical cicadas — those that emerge every 13 years and those that emerge every 17 years. Both are coming this year for the first time since 1803, but the 17-year cicadas will be prevalent in the Chicago area – while the 13-year brood will be seen in the southern half of the state.

3 cicada species, 3 cicada noises

There are three different species of 17-year cicada – with similar counterparts in the 13-year brood. They are known taxonomically as Magicicada cassini, Magicicada septendecula, and Magicicada septendecim.

Each of these species has a slightly different appearance, and a different noise it makes. As explained by the "Songs of Insects" guide, Magicicada cassini has a loud, high-pitched noise that features "numerous clicks, followed by a quickly rising buzz." Ohio nature blogger Lisa Rainsong compared cassini's buzz to "an electric string trimmer or weed whacker."

Rainsong also noted that cassini's buzz "swells and ebbs, then swells again – almost like an inhale and exhale."

Magicicada septendecula also buzzes, but the pattern is different. The Songs of Insects guide said compared with cassini, septendecula's songs are "not as loud, high-pitched, raspy, and feature a series of buzzes that become more rapid and transition into lisps."

Their steady, rhythmic buzzing, one might argue, might evoke the sound of a Pac-Man game.

Septendecim is the outlier of the group – it doesn't buzz so much as howl in a tone that might even evoke a whistling tea kettle. As Rainsong notes, the pattern of septendecim's howl makes it sound like it is saying, "pharaoh."

"PHA… raoh!" "PHA… raoh!"

But with billions of cicadas coming, the noise for someone walking past a grove of trees will be a massive cacophony of buzzing and howling.

How do cicadas make their noise?

As explained in Science Daily, cicadas make their sounds with a corrugated exoskeletal structure in the thorax called a tymbal. The tymbal is an organ with the specific purpose of producing sound, a category it shares like a rattlesnake's rattle – which some say sounds not unlike a cicada.

But while rattlesnakes rattle their tails as a warning when threatened, cicadas have no such ominous intent. Only the males make the noise, and they are calling out to attract a female mate.

Cicadas go through some fairly complex contortions to make their tymbals produce such sounds. Derke Hughes of the Naval Undersea Warfare Center told Science Daily that if a human body were like that of a cicada, it "would have a thick set of muscles on either side of your torso that would allow you to cave in your chest so far that all your ribs would buckle inward one at a time into a deformed position. Releasing the muscle would allow your ribs to snap back to their regular shape and then pulling the muscle again would repeat this."

Crickets – which tend to come out once the cicadas have said goodnight – operate similarly, as their chirp is also produced by males trying to woo female mates. But crickets make their sound by rubbing specialized body parts on their wings together – they do not have tymbals.

The "It's a Noisy Planet" program from the National Institutes of Health says cicadas can reach the volume of a lawnmower, a motorcycle, or a tractor.

Why are cicadas so loud?

Cicadas are very loud indeed. Extension entomologist P.J. Liesch of the University of Wisconsin-Madison told CBS 58 in Milwaukee that a grove of trees with a bunch of singing and screeching cicadas could reach 70 to 80 decibels – a similar volume to a vacuum cleaner.

Come closer, and it could be more like 90 to 100 decibels, Liesch told the station.

If the noise level for a mass of cicadas reaches 100 dB, that would place it louder than a food blender at 85 dB and a lawnmower at 94 dB.

Why are they so loud? A explained by Britannica, cicadas have air sacs that have resonant frequencies to amplify the sound they make with their tymbals, so their mating calls can be heard far and wide.

What about those other cicadas later in the summer?

After this year, the 17-year cicadas won't be back until 2041. But as any Chicagoan who has been around between July and October knows well, other kinds of cicadas – annual cicadas – are around every summer. And they're pretty noisy too.

Linne's cicada (Neotibicen linnei) comes around every summer and has been spotted from mid-June to mid-October, according to a 2021 guide to singing insects in the Chicago region. Among cicadas, their sound might be the one most evocative of a rattlesnake – the Songs of Insects guide describes it as "a steady pulsating rattle sounding like a saltshaker, before ending abruptly."

The dog-day cicada (Neotibicen canicularis) also comes out during summer days each year, peaking in mid-August, according the guide. It produces a high-pitched tone that sounds almost like an electrical hum up in the trees.

The lyric cicada (Neotibicen lyricen) also comes around every year between about July and September. It has a droning sound like the dog-day cicada, but with more vibration to resemble a power saw, the guide noted.

And what about that cicada that provides that pleasant twilight song for Chicago from about July to October? "Ee-oowee-oowee-oowee-ooweeeeeeee." That's the scissor-grinder cicada (Neotibicen pruinosa), and his sound is a sound of summer in Chicago right up there with the organ at Wrigley Field, jazz at the Museum of Contemporary Art, or a Grant Park Symphony Orchestra at Millennium Park. In fact, it may just chime right in during such concerts.

The Linne's, dog-day, lyric, and scissor-grinder cicadas will be coming to the Chicago area as usual, along with several other species, this summer after the 17-year cicadas have gone.