"We've had people say they sound like an alien ship landing, a house alarm sounding and chain-saws cutting timber," said Kris Braman, an entomologist with the University of Georgia College of Agricultural and Environmental Sciences.

Thirteen-year cicadas definitely attract attention when they visit.

Out of sight most of their lives, 13-year cicadas appear as adults -- well, once every 13 years. When their numbers are high, their presence is unmistakable. As some may recall, 1985 was such a year. And as many rural residents can attest this year, they're baaaack.

Annual cicadas, typically seen in the summer, have brown-black bodies, black eyes and clear wings. The 13-year cicadas are much spookier. They have vivid red eyes, black bodies and clear wings with orange stripes.

"The 13-year cicadas normally appear in heavily wooded areas, especially where lakes or streams are nearby," Braman said. "What makes them so noticeable is their numbers and the unusual sound they make."

Dog-day or annual cicadas, much larger than their 13-year cousins, make noise, too. "But people are accustomed to it as background noise in trees on hot summer days," Braman said.

The good news for people living where 13-year cicada numbers are high is that cicadas work normal hours.

"The males' song begins in the morning and subsides in the evening," Braman said. The males create the noise, she said, to attract the females. (You can hear cicadas on the World Wide Web at <www.biohaven.com/gallery>.) They have to do that, since adult cicadas live just long enough to mate and produce eggs.

The 13-year female cicada lays her eggs inside tree branches. The nymphs fall from the trees and develop in the soil, feeding on roots. Finally, the adults emerge from the ground, shed their skins and search for a mate.

"This whole process takes 13 years, and the adults are active for only about a month," Braman said. "Their skins can be found easily on trees and fence posts in the country."

Periodical cicadas include three 13-year and three 17-year species. "This 13-year brood of adults came out in May 1985, so we were expecting them this May," said Braman. "These adults should die out by the middle of June. And the new adults should emerge in May of 2011."

Braman said this species is found in the Southeast. It has been seen as far west as Louisiana and as far north as Illinois and southern Iowa. The 17-year cicadas are normally found in northern states. But they've been seen in eastern Tennessee and northern Georgia.

Thirteen-year cicadas are annoying but not harmful to humans. But they can seriously damage young trees.

"The damage comes from the female's laying eggs in tree limbs," Braman said. "She literally rips back the bark to insert her eggs. This can distort small trees with small canopies but causes little damage to large trees."

Native to the eastern United States, 13-year cicadas were described by New England colonists in the 1600s. In "New England's Memoriall" in 1669, Nathaniel Moreton described "a numerous company of flies, which were like for bigness unto wasps or bumble-bees."

The cicadas "came out of little holes in the ground, and did eat up the green things," Morton wrote. And they "made such a constant yelling noise as made all the woods ring of them, and ready to deaf the hearers."