UI The Daily Iowan, IA
06-29-07
For cicadas, the buzz is gone
Stephen Schmidt - The Daily Iowan
Media Credit: Ben Roberts/The Daily Iowan
Nature lovers who visit woodlands in eastern Iowa during the next few weeks
may notice what seems to be disturbing signs in the trees - empty shells, piles of
dead insects, and gnarled tree twigs.
But they shouldn't worry- these are actually signs of life.
The last remnants of Brood XIII, a swarm of black-bodied, red-eyed periodical
cicadas last seen in eastern Iowa 17 years ago, are now dying off. What's left is
their offspring.
University of Connecticut entomologist John Cooley said that in four to six weeks,
the small, white, ant-like nymphs will hatch from eggs nestled in swollen tree
twigs and fall to the ground. They will then burrow underground and attach
themselves to the tree roots, where they will use their pointed proboscises to
drink tree sap, waiting 17 years to emerge again.
Cooley, a cicada specialist, has been tracking the insects across the country with
fellow Connecticut entomologist David Marshall since 1995, leaping from one
brood to another in an effort to learn more about the phenomenon.
"I guess we're the ultimate groupies," Cooley said.
The cross-country trips are necessary because the life cycle of periodical cicadas
- which can either be 13 or 17 years depending on the brood - does not lend itself
to easy study. Except for the three to six weeks they spend mating above
ground, the majority of their lives is spent buried several inches to a foot
underground.
After counting changes within the trees and feeling the appropriate ground
temperature, the insects emerge, molting and flying to the forest canopy, Cooley
said. The males then begin the search for mates, singing with sound-producing
structures called "tymbals" located on their abdomen. Receptive female cicadas
respond with the rhythmic clicking of their wings, Cooley said. Once the
reproduction cycle is completed, the cicadas quickly begin to die.
Brood XIII is one of three periodical cicada broods in Iowa; it will return in the
year 2024.
The U.S. Department of Agriculture estimates that a female cicada will lay
between 400-600 eggs. Of those, only 2 percent will live past the first two years.
Donald Lewis, an extension entomologist at Iowa State University, said he
has records of Brood XIII occupying 12 Iowa counties when they last appeared in
1990, and he expects them to be in the same counties when he takes a census
after July 4. He added, however, that earlier records showed Brood XIII cicadas
in up to 22 Iowa counties, indicating their number may have decreased over time.
Mark Vitosh, the district forester for the Iowa Department of Natural Resources,
said there seem to be fewer cicadas then there were in the last brood he
experienced in 1997 - Brood III, located in central Iowa. He said a loss of tree
cover in developed counties could be to blame. In Johnson and Linn Counties,
for example, long-standing, deciduous trees that cicadas favor can now only be
found in scattered locations.
"It's being pieced apart by one house here, one development there, so we're
slowly destroying the natural resources for these cicadas," Vitosh said. "I think it's
a big issue that [county officials] as a whole need to look at from the perspective
of where they want to develop."
E-mail DI reporter Stephen Schmidt at:
stephen-schmidt@uiowa.ed