In this series, we'll be addressing some common questions from visitors and readers. Do you have a science question that has you stumped? Ask our museum scientists via our form here and we'll answer it on our blog!
How do cicadas make sound?
…and how are they so loud? Cicadas are the song of summer across the United States, Chicago included. Even just two miles from downtown the droning of cicadas in trees can be downright overwhelming in July and August afternoons. But cicadas are so small: how do they make such a powerful sound? With no vocal chords, no lungs, and no subwoofer it ought to be impossible to hear a cicada from a mile away and yet, it's not. The loudest cicadas can emit a sound at over 100 decibels, which can be heard over a mile and a half away.
If you suspect that cicadas make sound the same way that the cricket, that other noisy summer insect, does then you'd get points for effort, but no points for being correct. Crickets make sound by rubbing their wings together (not its legs!), and cicadas have a special organ called a tymbal that produces sound. The tymbal contains a series of ribs that buckle one after the other when the cicada flexes its muscles. Every time a rib buckles, the rib produces a click. Many clicks produce a buzzing sound. The action is like how a bendy straw makes sound: pulling and pushing the ribs of the bendy straw together makes a series of clicks. If you could push, pull, and twist a bendy straw hundreds of times a second the sound of the clicks would be so close together that you'd only hear a buzzing sound: this is how fast the cicada is able to vibrate its tymbal.
Chicagoans can hear several different species of cicada in the summer: the dog-day cicada, the Linne's cicada and the scissor-grinder cicada are all common. In fact, the author heard all three of these cicada calls through his window while writing this post. Click on the links above to hear the sound for each cicada and to learn more about each of these species.
Scissor-grinder cicada resting on a Chicago sidewalk. Photo by author.
And yes, some online sources will tell you that it's possible for a cicada to damage your hearing. This is technically true and at the same time, there’s no reason to worry. The very loudest cicada, at 108 decibels, would permanently damage your hearing if you held it up to your ear for two minutes straight. Chicago cicadas are not even close to being that loud. Even if we estimate them at 90 decibels, as loud as a motorcycle from 25 feet away, it would take 8 hours of continuous play time for it to damage your hearing. Cicadas are completely, absolutely harmless. Just loud. Very loud.
Nature Museum Volunteer
 Fleming, Nic. “The Loudest Insect in the World”. (2014, October 3). Retrieved August 8, 2017, from http://www.bbc.com/earth/story/20140929-the-loudest-insect-in-the-world
 Wolfram Alpha LLC. 2017. Wolfram|Alpha. Retrieved August 9, 2017 from https://m.wolframalpha.com/input/?i=furthest+distance+you+can+hear+100+dB&lk=3
 Young, D., and Bennet-Clark, H. C. “The Role of the Tymbal in Cicada Sound Production”. (1994, December 19). Retrieved August 7, 2017 from http://jeb.biologists.org/content/jexbio/198/4/1001.full.pdf
 The Song of Insects. 2017. Retrieved August 13, 2017 from http://songsofinsects.com/cicadas
 IAC Acoustics. “Comparative Examples of Noise Levels”. 2017. Retrieved August 8, 2017, from http://www.industrialnoisecontrol.com/comparative-noise-examples.htm
Do you have a science question that has you stumped? Ask our museum scientists via our form here and we'll answer it on our blog!