May 31, 2013
How Do Cicadas Make That Sound?
Lee Rannals for redOrbit.com - Your Universe Online
Scientists are looking into how cicadas are able to make those extraordinarily loud sounds that annoy us all throughout the summer.
A research team from the Naval Undersea Warfare Center (NUWC) looked into cicadas' unique ability to produce these loud noises, which paves the way to make devices that would mimic it for remote sensing underwater, ship-to-ship communications, rescue operations and other applications.
Scientists carefully analyzed the physical properties of the cicada using lasers to measure the vibration of the insect's "tymbal," which is the exoskeleton on the insect responsible for its sound. Their analysis shows that the insects manage to produce their unmistakable sound because they have a unique anatomy that combines a ribbed membrane on the torso that vibrates when they deform their bodies.
Derke Hughes, a researcher at the Naval Undersea Warfare Center, said that to understand how the cicada makes its sound, you would have to imagine pulling your ribs to the point of buckling collapse, releasing them and then repeating that cycle.
If humans had bodies like cicadas, then we would have a thick set of muscles on either side of our torso that would allow us to cave in our chests so far that all our ribs would buckle inward one at a time into a deformed position. When the muscles release, it would allow the ribs to snap back to their regular shape and then pulling the muscle again would repeat this. Cicadas repeat this cycle for its left and right sides about 300 to 400 times a second.
Replicating the cicada's sound is difficult because it involves multiple moving parts, the buckling is not a uniform process, and the tymbal surfaces vibrate out of phase with each other and then somehow combine to make a sound that drowns out even the noisiest summer barbecues.
Cicadas make this sound to attract nearby females, who respond by snapping their wings. When males hear the wings snapping, they move in closer. As the males approach the female, the sound gets softer. Hughes and colleagues were able to trick the male cicadas into creating this noise by making a snapping sound that mimics the female.
Billions of cicadas emerged to create a chorus throughout the east coast this month. The Brood II cicadas are one of seven different species of periodical cicadas. The group only emerges every 17 years to mate when the ground temperatures are just right. After mating is done, the offspring return back to the ground and will not reemerge until 2030.
Brood II cicadas tend to swarm more than other species, sometimes getting as dense as 1.5 million cicadas per square acre. Females of this species are able to lay as many as 600 eggs before they die. The cicada storm allowed scientists like Hughes the opportunity to further their research on these bizarre yet fascinating insects.