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The Buzz on Brood XIX
Posted By kirkwoj On September 2, 2011 @ 2:10 pm In Bright Ideas, Summer 2011 | No Comments
This crop of cicadas, known as Brood XIX, operates on a 13-year cycle. Males are responsible for the noise, which they produce by vibrating ridged membranes on their abdomens.
Todd Ricketts, associate professor at the Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, measured the cicadas’ sound level at peaks of 85 to 88 decibels outside Vanderbilt University Medical Center on May 24. These levels are comparable to a motorcycle or subway at 25 feet. Stand too close for too long, and these vocal insects could damage your hearing, Ricketts says.
Cicadas caused problems with cooling systems across campus, says Mark Petty, assistant vice chancellor for plant operations. Most Vanderbilt buildings have cooling towers, which essentially push air over chilled water. Cooling-tower motors emit a frequency that amounts to a siren’s song for the insects.
“The cicadas end up dying in large numbers in and around the cooling towers, and their little carcasses plug up the strainers,” Petty explains. “We have to shut down the tower to clean it out, and while the tower is down, the building doesn’t receive any cooling.”
The cicadas’ appearance also gave new life to an urban legend that researchers were paying as much as $3,000 for specimens of rare blue-eyed cicadas. While most cicadas have bright red eyes, a very small percentage has blue or white eyes, confirms Patrick Abbot, associate professor of biological sciences, “but the idea of anyone paying for them is a recurrent myth.”
During the last cicada emergence in 1998, Glenn Webb, professor of mathematics, became interested in why cicadas emerge only at yearly intervals that are prime numbers. He created a model with periodic cicadas and hypothetical predators on two- and three-year life cycles, and found that by emerging every 13 or 17 years, the cicadas better ensured their survival.
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