It is time once again for the "17-year locusts" to hatch in the Mercer County area, posing a danger to young trees and sensitive eardrums.

The locusts -- more accurately called cicadas -- are spread widely over the eastern half of the United States, but are found nowhere else in the world, according to Tom Zundel, an agent with Mercer County Cooperative Extension.

In locust years, more than a dozen different broods of cicadas emerge from the ground, where they have spent 17 years as larvae.

"They have not been a big problem in Mercer County -- yet," Zundel said. "The cicadas have been coming out in the mountain areas, which is a surprise, but with warmer weather, I expect to see them hatch here by next week," he said.

After mating, the female cicada looks for pencil-sized twigs in which to lay eggs, Zundel said. That results in "slagging" or killing the branch. A single cicada can lay eggs in 50 or more locations with more than 100 eggs per laying, he said.

Small trees die upon slagging, he said, but trees that are 35 years or older should weather the wear.

"The branches of older trees will die with the egg laying, but the rest of the tree should be fine," Zundel said.

To protect young trees, Zundel suggests using sheets of cheese cloth.

"Wrap the cloth around the entire tree to the base of the trunk for small trunks," he said. "You need to do this when you start hearing them 'sing' and leave it on for two to three weeks until they die," he said.

During the few weeks that cicadas spend above ground before dying, they are consumed with mating. It is the male's high-pitched mating call that can be bothersome.

"They are quite loud, as I remember," Zundel said.

The high-pitched "scream" is created by the ribbed membranes on the insect's back and is amplified as it passes through the hollow of the abdomen.

"We are expecting many reports any time now of the broods hatching," Zundel said.

As these cicadas begin to bug the area, Mill Creek Metro Park, Youngstown, is planning two programs.

"Cicada Invasion" will be at 2 p.m. Saturday at the Ford Nature Center and "Periodical Cicadas: The Plague and the Puzzle" will be at 2 p.m. Sunday at the center.

Call (330) 740-7107 by Thursday to register.