Ed Bennett — a fan of myNoise — shares one of his most memorable audio memories with us: "It was the summer of 1987 in Chicago, Illinois, and we had a cicada emergence. It happens once every 17 years. That day, I walked deep into the forest to experience the event and stood surrounded by millions of singing insects. Waves of sound rose and fell as cicada groups synchronized into a huge chorus. It was overwhelming."
Ed never forgot that experience and looked forward to this year, as end of May/early June 2021 saw the resurgence of Brood X (Brood 10) — one of the 15 broods of periodical cicadas that appear regularly throughout the eastern United States. Ed even bought a surround-recording device for that special occasion and was kind enough to share his recordings will us.
Ed: "These recordings were made in locations near my current home in Ellicott City, Maryland, including my back and front yard, neighbors' trees, and the 300 wooded acres of Centennial Park — which had the densest concentrations of cicadas."
Thank you so much, Ed!
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It is fascinating how the cicadas of Brood X manage to emerge all at the same time, after spending 17 years underground! Why did they wait for so long? The answer might come from natural selection.
Cicadas' predators, creatures like birds and rodents, have a typical life cycle of two to six years. While these predators gorge themselves and reproduce like mad when cicadas emerge in huge numbers, their growth is limited in time, since a whole generation of predators will die before the next cicada emergence will arise. If cicadas had a shorter evolutionary cycle, they would constantly feed their predators, whose population would then become a threat to the cicada population.
Cicada cycles often coincide with prime numbers - say, every 13 or 17 years. This allows them to minimize the chance of two broods waking up simultaneously, which would carry the risk of both broods disappearing forever, if there were a large number of predators that year.
The noise you hear consists of two components: a narrow-band frequency distribution located at around 1.2 kHz and a wider band at 6 kHz. The lower distribution corresponds to thousands of males producing their mating call, which sounds like "eeeeeeeeeehooo" when you are close enough to hear an individual specimen. At large scale and from a distance, the superimposition of all these individual calls just produces noise, as illustrated by the first slider. The second frequency distribution is the regular cicada noise, which often comes in waves. These waves are illustrated in the right-most sliders.
Published on June 21st, 2021