CHICAGO (NewsNation Now) — They’re loud, they’re kind of creepy looking and they’re emerging again in areas across the country.

You may have seen or heard these cicadas near you. A periodical cicada brood is crawling out of the ground after 17 years.

“Brood X is the biggest part of the emergence is the western half of Ohio, all of Indiana, the eastern border states of Illinois and a little bit of northern Kentucky,” said David Shetlar, PhD. at Ohio State University.

Scientists use Roman numerals to number the broods, which Shetlar pointed out can lead to some confusion and lead people to think it’s “brood ex.”

While they may be loud, cicadas are completely harmless, according to Shetlar.

“The only thing that they would harm would be the roots of trees and shrubs as a nymph,” said Shetlar. “As adults, they do suck a little juice, mainly to get water and a little bit of sugar out of the tree branches and things like that. But the only damage that’s actually done is by the female when she lays her eggs. She lays her eggs in small, pencil-sized branches, and that will often kill that branch and cause what we call flagging — which is just that the branch turns brown on the tip of the tree.”

Watch the full interview with David Shetlar in the player above.