What’s all that noise? Cicadas!

March 15th, 2011

Millions of those red-eyed bugs will come out of the ground this spring, but don’t worry

A swarm of critters that emerges from underground every 13 years will fill the air over much of the Southeast with their ear-splitting mating calls.

Scientist call them periodical cicadas, Brood 19. Writers often mislabel the red-eyed, 11/2-inch-long insects as locusts, as in biblical plagues.

As ground temperatures approach 64 degrees, the four species of 13-year cicadas will dig out at night from burrows where they have sucked sap from roots for more than a decade.

Cool – or yuck, depending on your sensibilities.

Entomologists don’t know exactly what triggers their emergence, but the date does not vary much among generations.

“Periodic cicadas are amazing in their ability to be synchronized,” said Clemson University entomologist Eric Benson. “Almost overnight, tens of thousands emerge in an area. It’s something to behold.”

He predicts the swarms will rise in late April or early May, based on spring weather and the behavior of the cicadas in 1998, the year of the most recent emergence.

Other species of smaller cicadas come around every year.

Concentrations of the 13-year variety have been known to reach 1.5million per acre in some places. But more commonly, the density is in the hundreds of thousands per acre, scientists say.

The Mecklenburg County parks department will conduct a citizen scientist project to see where and when the cicadas emerge.

“You only have a month to study something that happens every 13 years,” said J.C. Chong of the Pee Dee Research and Education Center in Florence, S.C.

A rural phenomenon

City slickers are less likely to notice the bugs. The cicadas stay where there are lots of trees and shrubs and the soil is undisturbed. They favor hardwoods and have a particular taste for oaks.

But country folk, hunters, hikers and other outdoorsy types will find them in woods across the Carolinas.

“I remember walking in Greenwood State Park,” said Andy Boone, a forest entomologist who worked at the South Carolina Forestry Commission during the 1998 event. “They were all over the place.”

Periodical cicadas aren’t beachcombers. They are not readily found in places where the soil is moist, as in the coastal plains.

Yet where they cruise for mates, their presence is unmistakable. Their crispy brown carcasses litter the ground after their short flings. They leave millions of eggs tucked into tender branches of young trees and plants.

Within weeks, the babies, which look like tiny ants, drop to the ground and start digging for a place to develop – for 13 years.

Besides their odd life cycle, the cicadas’ most memorable feature is their love song.

Males vibrate membranes on their bodies that emit calls to females. But the boys are choosy. Each species emits a specific song, and the sound lures only females in that species, scientists say.

The male cicada gets around. He mates several times, as do the females. But the boys are busier. Each female lays as many as 600 eggs.

Love-starved critters

When the sounds from four species combine, it’s a chorus of noises.

The tune is a shout. It can reach the 100-decible range from one love-starved bug. That’s about the same as the roar of a motorcycle or standing within 3 feet of a lawn mower.

Some scientists say periodical cicadas are the loudest insect in the world.

“If you’re not in a car, you can hear them from several miles away,” Boone said of his excursions into the South Carolina woods 13 years ago. “It sounded like a busy airport taxiway.”

He estimated the volume reached 80 to 90 decibels and compared the sound to churning ball bearings “that are not quite in synchronization.”

After a while, though, the noise fades into the background. Much as a homeowner grows accustomed to the passing train whistle near his house, “Your brain processes it and you don’t hear it,” Boone said. “It’s like white noise.”

Both genders of cicadas die when the mating cycle is complete, within six to 10 weeks.

The insects are relatively harmless, scientists say. They are not poisonous. They don’t transmit disease. They have few predators, other than pesky fungal parasites.

“They don’t bite,” said Tim Mousseau, an entomologist at the University of South Carolina. “They’re not interested in (garden) plants. They don’t eat crops.”

Only young trees and shrubs are vulnerable, and then only if they happen to be where the infestation is particularly intense, he said.

Too many young cicadas feeding on branches can damage or kill their host.

Entomologists recommend that growers either refrain from planting the year before an emergence or that targeted fauna be covered with screening material.

Meanwhile, the bugs sure are tasty to birds, spiders, snakes – even the family pet.

There are so many cicadas that nature allows hungry animals to feast until they’re full. But that still doesn’t significantly reduce the population.

Cool? Yuck.

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