The Secret Behind That Cicada Sound

Cicadas have a unique system of noise-making.

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Cicadas Have Been Around for a Long Time

Cicadas emit one of the most distinct sounds of the animal kingdom—of the insect group, anyway. The song of the cicada is a reverberating noise that's hard to describe and even harder to re-create. They belong to a superfamily, the Cicadoidea, and there are more than 3,000 known species of cicadas. Evolutionary biologists have determined that these exceptionally loud bugs have been present in North America for millions of years. Fossils of cicadas have also been discovered in Eurasia and South America, dating back to the Jurassic and Lower Cretaceous periods. Having been around for as long as they have, cicadas have served many purposes in various cultures—used as religious symbols, as a food source, for medicinal purposes, and as an indication of a change in weather and changing seasons. Cicadas even make an appearance in cultural mythologies, literature, and music.

Why Are Cicadas So Loud?

One of their defining features is the sheer volume of their singing, which can reach as much as 100 decibels. Such a volume is equivalent to the sound of a lawnmower, dirt bike, or tractor, according to The U.S. Department of Health & Human Services. So, where does it come from? "Secrets of the cicada's sound," 2013 research provided by the Acoustical Society of America and shared by ScienceDaily, describes the sound as well as the work that a team of U.S. Naval researchers has been doing to demystify the subject: "Their analysis shows that the insects manage to produce their incredibly large sound because they have a unique anatomy that combines a ribbed membrane on the torso that vibrates when they deform their bodies." In other words, it's not vocal cords making that cicada sound.

According to ScienceDaily, Derke Hughes, a research engineer at the Naval Undersea Warfare Center, describes this process as such:

"If your body were like that of a cicada, […] you 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. The cicada repeats this cycle for its left and right sides about 300 to 400 times a second."

It's a unique system of noise-making, and the result is a phenomenon we hear echoing across the landscape once the soil warms up and the cicadas emerge from the ground. This happens in routine intervals of either every 13 or 17 years, which usually occurs in May or June as they prefer warm, dry weather. Once they emerge, they spend about four to six weeks mating and laying eggs in the openings of the bark on tree trunks and branches. At least, this is true of periodical cicadas, a genus exclusive to North American regions known as Magicicada. Annual cicadas emerge every year, as the name suggests.

It's not just the droning, though. According to the U.S. Geological Survey, "Cicadas make a variety of sounds, including very loud buzzing sounds. The males have tymbal organs that include rib-like bands on a membrane that can be vibrated very rapidly by a special muscle. The sounds include courtship calls and squawking sounds when the cicada is handled or disturbed." If you're curious, you can hear an audio recording of the sounds of cicadas here.

Along with buzzing and squawking, cicadas are also known to produce rhythmic ticks, high-pitched whines, and even a more musical-sounding song. Despite the sometimes deafening sounds they produce and the fact that they descend upon us by the millions, cicadas are absolutely harmless, to both humans and our pets. They do not bite or sting and will do little more than "scream" if you disturb one. So, unless you just have an (understandable) insect phobia, you have nothing to be afraid of.

Cicada calls are hard to miss. They're the soundtrack of so many Southern evenings. You've likely been familiar with them for a long time, but now you know exactly how these insects make the sounds we associate with our Southern summers.

Have you ever wondered about the song of the cicada? Keep an ear out—you're sure to hear the telltale cicada drone if you step outside during the warm months.

Source: Acoustical Society of America (ASA). "Secrets of the cicada's sound." ScienceDaily. ScienceDaily, 30 May 2013.

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