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They\'re Here - Cicada Cycle Fascinates US

13.05.2004  |  123× přečteno      vytisknout článek

They\'re Here - Cicada Cycle Fascinates US

WASHINGTON - The first cicada of the season sat on the doorstep like a mutant bumblebee, with red eyes and yellow legs.

But, apparently alarmed by the appearance of a human, it tumbled off the shallow step, landing helplessly on its back. Its yellow legs wiggled frantically to no effect.

How could anything so stupid and clumsy survive, and prosper in such huge numbers? Billions, probably trillions, of cicadas are emerging this month across the eastern United States in a monster swarm known as Brood X or brood 10.

Scientists plan to study the mass coming out of Brood X to find out. Did their bizarre 17-year cycle evolve because they are such easy prey, or did it allow them to evolve into the clumsy, noisy creatures that they are?

\"Brood X is likely to be the largest insect emergence on Earth,\" said Keith Clay, a cicada expert at Indiana University.

Starting this week, across much of the eastern United States, from Georgia north to southern New York and as far west as Illinois, the cicadas will emerge from their 17 years of sucking on tree roots underground to engage in a two-week orgy of calling, mating, laying eggs and then dying.

And things that eat cicadas, from fish and birds to dogs, will gorge on them in a mad frenzy.

If history is anything to go by, their noise will drive barbecues indoors, disrupt weddings and graduations and waken children. Then they will die en masse.

\"They rot very quickly and they smell really bad for a few days and will disappear on their own,\" Clay said.


Clay says cicadas can reach densities of up to a ton an acre, or 3,000 kg per hectare. He believes humans are altering the environment to make it more hospitable to cicadas, by creating little patches of forest that have lots of edges -- which the insects appear to prefer.

Understanding cicadas could help scientists understand other animals whose life cycles are affected by human activity, including white-tailed deer and the ticks that carry Lyme disease, Clay told a news conference at the National Science Foundation, which sponsors his work.

Cicadas are notable not only for their vast numbers, but also the noise they make. Different species have different calls, says University of Connecticut biologist Christine Simon.

\"(One species) sound like flying saucers from a 1950s science fiction film,\" Simon said. Another species sounds like \"somebody took water and threw it into hot fat. It is a loud, sizzling noise,\" she said.

The thumb-sized insects are found in many countries around the world but the dramatic periodical cicadas of the genus Magicicada are found only in eastern North America. There are seven known species with 17- and 13-year life cycles.

Simon believes the 17-year cicadas evolved when the 13-year cicadas, for whatever reason, developed a four-year dormancy period.

She also believes some dramatic climatic disturbance since the last Ice Age 10,000 years ago favored the development of the 17-year cycle. The cicadas locked in the behavior.

\"I think it\'s just an accident that they became periodical,\" Simon said.

Scientists agree the mass emergence of billions of bugs has allowed the cicadas to survive even though just about anything will eat them.

\"We prefer the term \'predator foolhardy\' to stupid,\" Simon said.

But she notes not all their behavior is overly bumbling. For instance, when a male calls a female his buzz takes one tone, and the female makes a flicking sound to answer during a lull. The male\'s call changes substantially after that.

\"He\'ll start pawing her front legs,\" she said. His mechanical-sounding whir will change again, to a kind of chuckling. \"While he\'s doing that, he\'ll mate with her,\" Simon said.

Story by Maggie Fox, Health and Science Correspondent


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