Cicada Swarm Returns Underground

John Roach
for National Geographic News
August 2, 2004

Brood X is gone from sight, plotting underground for a return in 17 years.

This spring and early summer, billions of black, shrimp-size bugs with transparent wings and beady red eyes carpeted trees from the U.S. eastern seaboard west through Indiana and south to Tennessee. By the middle of July they were gone, not to be heard or seen from again for 17 years.

"I will miss the stars of Brood X (their air acrobatics, those pretty eyes, and friendliness) and hope their little ones make it safely back into the Earth," read a goodbye message posted June 30 by Deborah, from Wayne County, Michigan, on the Cicada Mania Web site message board.

The bugs belong to the largest group, or brood, of periodical cicadas—insects that spend most of their lives as nymphs, burrowed underground and sucking sap from tree roots. They emerge once every 17 years, transform into adults, do the business of reproduction, and then die.

The cacophony of their courtship ritual disturbs suburban tranquility, and their nests can kill young tree branches. Females make slits in the branches and deposit their eggs inside. The process leaves many treetops with brown, dangling limbs flapping in the wind.

In addition to being a nuisance, the mass emergence aerates the soil, provides a feast to thousands of animals, prunes the treetops, and provides a pulse of nutrients into the environment, scientists say.


There are at least 12 broods of 17-year cicadas, plus another three broods that emerge every 13 years. "A brood is a class-year, like the graduates of 2004," said Gene Kritsky, a biologist and cicada expert at the College of Mount St. Joseph in Cincinnati, Ohio.

A brood emerges almost every year somewhere, sometimes overlapping with others. But none of the emergences matches the pure size of Brood X, which includes three cicada species: Magicicada septendecim, Magicicada cassini, and Magicicada septendecula.

Keith Clay, a biologist at Indiana University in Bloomington is engaged in a long-term study of the Brood X cicadas. He said people's reaction to the 17-year phenomenon runs from disgust to awe.

"Some people leave town and go west, where there are no cicadas. Other people plan camping trips timed in the middle of the outbreak, because they want to experience it in its full intensity," he said.

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