Sept. 12 (UPI) -- The National Weather Service shared radar images showing massive swarms of migrating dragonflies over three states.
The NWS' Cleveland Office tweeted radar images showing the insects creating storm cloud-like shapes over Ohio, Indiana and Pennsylvania.
Norman Johnson, a professor of entomology at Ohio State University, said the dragonflies are likely green darners on their way south for the fall. He said large swarms of the insects are unusual, but can occur when local weather causes them to cluster.
"The big swarms have been recorded a lot over the years, but they're not regular," he told CNN.