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The science of the sound of cicadas and their shrill songs

Weather shut down cicada chorusing over the weekend, but their shrieking has returned

Capital Weather Gang’s Kevin Ambrose measures the decibel level generated by cicadas in Oakton, Va. on May 27. (Video: Kevin Ambrose)

The noise level of cicadas in our area has been deafening at times, particularly during warm, sunny afternoons. The bugs have reached 90 decibels in places; it’s like standing next to a food blender spinning at top speed or a gas-powered lawn mower.

The sound we are hearing is chorusing, and it’s produced when male cicadas vibrate their tymbals, a noise-producing organ on the side of their abdomen, in the hope of attracting females to mate.

But this past weekend, when temperatures fell into the 40s and 50s with rain, the cicadas suddenly went silent. And they stopped flying. It seemed like they had mysteriously disappeared.

Cicadas feel the chill and have shut down, but they’ll bounce back

However, by Monday and Tuesday, when the sun appeared and the temperature rose back into the 70s, the cicadas became as active and loud as they were the previous week. It’s apparent cicadas don’t like to mate when it’s cold, dark and wet outside.

Brood X comprises three species of cicadas, and each has a different sound

Brood X cicadas that have emerged in the D.C. area are from three separate species — Magicicada septendecim, Magicicada cassini, and Magicicada septendecula — and each species has a distinct sound.

Paula Shrewsbury, a professor of entomology at the University of Maryland, described in an email the various sounds of the cicada species:

  • “The higher pitched 'pulsers’ are Magicicada cassini.”
  • “The almost background 'whir’ sound is from Magiciada septendecim.”
  • “The third species (Magicicada) septendecula is less common and (is) more of repeated chirp call.”

The highest noise level often occurs under a tree that has collected many Magicicada cassini males that pulse loudly every few seconds. Away from individual trees, the sound of cicada chorusing blends into a constant hum.

“[A] few males of a species start singing in a tree and attract other males of the same species all with the ultimate goal to attract females to share their genes with,” Shrewsbury explained. “You end up with lots of males of a species ‘chorusing’ in a tree.”

How cicadas make their noise

Daniel Gruner, also a professor of entomology at the University of Maryland, wrote in an email that only males can make the vibrational sounds you hear outside.

“The tymbal organs are like a pair of drums stretched across either side of the space between the thorax and abdomen. The male abdomen is hollow and acts as a resonance chamber to amplify their songs,” he wrote. “The females lack the tymbals, while their abdomens contain the machinery for egg production and oviposition.”

Cicadas make distress calls

Besides chorusing, cicadas make distress calls when they are disturbed. It’s a loud, shrill sound. “If the cicada raises a ruckus when you handle it, it must be a hysterical male,” Gruner wrote. “By comparison, the females are calm, stoic, and silent.”

Male cicadas also make distress calls when animals eat them. Two days ago, one of my two dachshunds, Peanut, ate a cicada that was screeching as it was swallowed. That cicada continued its distress calls from inside my dog for 20+ seconds. Finally, I picked up Peanut, and the sound was quite clear and distinct, projecting from inside her stomach. It was sad but fascinating.

My name is Max, and I have a cicada problem

How much longer should we expect to hear cicada chorusing?

“Since we still have cicadas emerging, I would estimate a good two weeks,” wrote Shrewsbury in an email. “Weather may influence this timeline.”

And Gruner responded, “I would expect at least 1-2 weeks given their expected life span and the fact that I am still seeing nymphs and a few emerging individuals from the cooler forest nearby. I do think we are near the peak, either just passing it or just approaching it, given the adult mortality starting to accumulate.”