A brood of cicadas that slumbered underground for nearly 17 years is emerging in parts of eastern Ohio — crawling, flying and hitting buildings and trees.

“Some people are creeped out,” said Eric Barrett, an assistant professor and Ohio State University Extension educator in Mahoning County, in a news release issued Tuesday by the Ohio State University College of Food, Agricultural and Environmental Sciences (CFAES).

“We’re trying to help people not overreact,” he said.

The 17-year cicadas — called periodical — arrive in the millions, coming out of the ground and maneuvering out of their shells. They go looking for a mate, with the males announcing their arrival with an incessant buzzing — their mating call.

The early sightings of this brood of 17-year cicadas in Ohio have been in five counties: Jefferson, Columbiana, Mahoning, Stark and Trumbull. A brood is a population of 17-year cicadas. Different broods emerge in different parts of the United States on their own cycles; a brood active in Summit County last emerged in 2016 and won't resurface until 2033.

Barrett said the cicadas don’t bite, don’t suck blood or do much harm to trees. But young shrubs or trees under 5 feet tall could benefit from having netting, such as cheesecloth, spread over them to keep the female cicadas from making slits into small branches in which they deposit eggs.

People can be citizen scientists and track, photograph and map the 17-year cicadas using a new mobile app developed at Mount St. Joseph University in Cincinnati.

“We developed this app because so many people are fascinated by cicadas,” Gene Kritsky, dean of behavioral and natural sciences at Mount St. Joseph said in a news release.

Kritsky said the periodical cicadas are “generational events,” used by many people to mark the passage of time and recall events in their lives.

People can use the app to help Mount St. Joseph map the cicadas to verify where they are emerging.

The app is available for free at the app store for download. People can then photograph the insects and submit pictures to be included on Mount St. Joseph’s cicada map.

The 17-year cicada differs from the annual cicada that arrives each summer in July and August, said the news release from Ohio State’s CFAES. The two types look and sound distinct.

Once they come out of the ground and shed their outer covering, 17-year cicadas become adults with red eyes, black bodies, and yellowish-orange wings. Annual cicadas have brown or green bodies, black or brown eyes, and black or green-tinged wings.

Far from the looks of the cicadas, what sets the 17-year cicadas apart is their mating call.

“It’s a remarkable thing. It can also get on your nerves,” said David Shetlar, a professor emeritus with CFAES.

He said it also “can be annoying for the cat or dog owner who watches his pet come in from the yard and upchuck some cicadas because he ate too many of them.” Shetlar said.