Experts first thought they looked like a chain of late-summer rain showers appearing on doppler-radar scans from the National Weather Service.

By Zee Krstic
September 16, 2019
Chirag Sankaliya / Getty Images

If you happened to check online weather radars last week, you could have wondered if most parts of Virginia, Pennsylvania, Ohio, and Indiana were in for a bout of very wet weather—but as most meteorologists soon realized, radars weren't picking up storm systems. According to the National Weather Service, green blotches of inclement weather on national radars turned out to be rather large swarms of dragonflies, CNN reports. They appear to be green darner dragonflies, which head south for the winter every year; while dragonflies are known to be solitary creatures, a gradual change in weather systems may have led to the change in behavior. 

Norman Johnson, an entomology professor at Ohio State University, told CNN that nearly state-wide swarms like these are normally rare occurrences. He says that entomologists and other experts haven't worked out all the details of dragonfly migration patterns yet, but they do know that dragonflies can use their intricate wings to cover an average of eight miles each day, with some flying as far as 86 miles in the same period.

Related: The Best Places for Birdwatching in the United States 

Based on the radar that meteorologists saw last week, some social media users wondered if there was any danger; but CNN reports that experts believe locals in the region should expect a fascinating display of nature and nothing more. 

This isn't the first time that meteorologists have caught something other than thunderstorms on their radars; the National Weather Service often tracks the seasonal migration of birds across the country, as well as others, like bees. "We can now predict when we will see waves of birds all through radar and knowledge," Dr. Sara Kross, a master's program director in the department of ecology, evolution, and conservation biology at Columbia University, told the New York Times. "Right now, because of radar, we can see it happening in real time."

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