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Millions of cicadas that were dormant underground for 17 years will emerge in parts of Ohio

Periodical Cicada Pennsylvania
Posted at 8:00 AM, Jan 30, 2021
and last updated 2021-01-30 08:01:06-05

CLEVELAND — Billions of cicadas that have spent 17 years underground will emerge across most of the eastern part of the United States, including parts of Ohio, with their signature loud, ceaseless buzzing.

Brood X is scheduled to emerge in parts of western Ohio, including Cincinnati and Dayton, in mid-May and June, for the first time since 2004. A brood is a large population of cicadas that emerges from the soil at the same time.

The Brood X cicadas are a family of periodical cicadas that shouldn’t be confused with the annual cicadas typically known as the dog cicadas that are heard all over Ohio in late summer.

Dr. Gavin Svenson, director of research and collections and curator of Invertebrate Zoology at the Cleveland Museum of Natural History, said while we won’t see any cicadas of the Brood X in Northern Ohio, their presence in other parts of Ohio and the eastern part of the U.S. are worth following, calling it a biological phenomenon.

“This doesn't happen in other places. It's not like this is happening in Mexico or this is happening in other areas in the world. I mean, this is a really cool Eastern United States thing,” Svenson said.

Brood X is one of seven species of periodical cicadas that are distributed all over the eastern United States. The last time Northeast Ohio saw mass numbers of periodical cicadas was in 2016 when Brood V emerged after 17 years in the ground.

A map created by the USDA Forest Service shows the distribution of broods and years of emergence.

Svenson said in any particular year, one of these broods could emerge somewhere in the eastern part of the country, with each group of periodical cicadas on their own timetable.

“Nobody really knows why (it's) 17 years. There have been all sorts of ideas, like its predator avoidance, it’s an evolutionary strategy because they're a big food source, so a lot of things would target in on eating them,” he said.

When the Brood V caused a big ruckus in 2016, they all mated and laid eggs that were deposited into the ground, and the clock starts ticking again. That group will emerge in 2033.

So how do periodical cicadas count the years?

Essentially, it’s unknown. While underground, they are in their nymphal form, spending their entire time a couple of feet into the earth. While under the soil, they feed on the sap of tree roots. Researchers believe they are picking up on the chemical signals in deciduous trees as they go into dormancy and lose leaves.

"The idea is that these things [cicadas] have some sort of molecular clock that cues into the number of tree cycles that they've detected ... and some get it wrong. And they're called the laggers," he said. "Every area gets those kinds of circumstances where somebody finds a periodical cicada, and it's an off-year. It's like, what the heck happened here? They made a mistake. I mean, biology makes mistakes all the time, and it's not perfect."

Come summer, Svenson said the cicadas of Brood X are totally harmless, but their presence in large numbers can be annoying to anyone gathering outside.

A big part of why the periodical cicadas are emerging earlier and earlier is due to climate change. Svenson said museums have a collection of cicadas from over the last hundred years.

"If you look on the dates of the labels when these things were collected, it was typically in late May. But as the years click on, they're emerging earlier and earlier in the year, so you could actually see evidence of a change in climate because the ground temperature is getting warmer, you know, weeks earlier than it used to," Svenson said.