(Part two of a series on cicadas)
By Marcia Anderson
Billions of flying bugs known as cicadas are currently sweeping over the East Coast. What were you doing in June of 1996? Do you remember the terrible sound they made? Cicadas are a true marvel of nature and one that should be enjoyed whenever possible. Once it starts, the emergence typically lasts only four to six weeks: long enough for the males to sing their mating song, the cicadas to mate, the females to lay their eggs, and then they all die, leaving their 2-inch corpses for us to clean up.
The song of the cicada was used to signify summer in Japanese cinematography. Standing near an especially loud chorus of cicadas can be like standing near a motorcycle, with a racket reaching up to 100 decibels. Because cicadas produce extremely loud noises while requiring very little power, they are being studied by the U.S. Navy. They are of particular interest in naval sonar research related to underwater exploration and communication.
How do the cicadas make that sound? First, only male cicadas make the sound. Males have organs that resemble drum-like plates, called tymbals, on both sides of their abdomen. The cicada moves his muscles to pop the tymbals in and out, which creates the sound we hear. These chirping and clicking noises can be heard by females up to a mile away.
The naval research facility in Newport, Rhode Island uses microcomputer tomography to image a cicada’s tymbal. This is like a CT scan that picks up details as small as a micron in size. The tymbal is made of a thin membrane connecting thicker sections known as ribs, each of which is thinner than a human hair. According to researchers, the male cicada pulls all the tymbal ribs inward and together. The ribs make a short, sharp noise when they draw together and again when they snap apart. The cicada repeats the action 300 to 400 times per second, creating the characteristic deafening chirp. Producing noise in this way is unusual in the insect world. For example, crickets, locusts, and katydids rub their legs to create their chirps.
Interestingly, the cicada’s left and right tymbals can act like two speakers that produce sound waves that combine. Imagine two water waves in the ocean, generated by separate storms converging toward each other. Where the peaks of the two waves perfectly overlap, they add together and spike much higher than the peak of either wave alone. We call this very large wave a rogue wave, which is known to have sunken many an unsuspecting ship in the deep sea. Similarly, if the waves are sound waves traveling through the air, the peaks would be spots where the volume is very high. The cicadas may use this effect to pump their volume to very high levels without expending as much energy as if a single tymbal had to do it alone.
Children and adults can experience this phenomenon by catching a male cicada and then gently closing their hands around it to feel the vibrations emitted by its chirping.
Warning: During cicada season they may land on you if you’re using a power tool or lawn mower. Why? Cicadas think the sounds made by power tools and lawn maintenance equipment are made by other cicadas. They get confused and will land on the people using the equipment! So either cut your lawn in the early morning or near dusk when the cicadas are less active, or let the grass grow a little longer for a few weeks.
For more cicada information: The scientific name for these cicadas is Magicicada. The National Geographic Society supports the Magicicada website: http://cicadiamania.com.
About the Author: Marcia is the bed bug and vector management specialist for the Pesticides Program in Edison. She has a BS in Biology from Monmouth, second degree in Environmental Design-Landscape Architecture from Rutgers, Masters in Instruction and Curriculum from Kean, and is a PhD in Environmental Management candidate from Montclair – specializing in Integrated Pest Management and Environmental Communications. Prior to EPA, and concurrently, she has been a professor of Earth and Environmental Studies, Geology and Oceanography at Kean University for 14 years.