Radar dragonflies

A typical image from a radar at the National Weather Service in Wakefield is shown on the left. On the right, an image captured Monday, Sept. 16, 2019, showing what meteorologists think was a cloud of dragonflies so massive it appeared on radar. 

Today’s forecast: Partly cloudy with a chance of dragonflies.

Lots and lots of dragonflies. So many, they’ve been showing up as pulsing clouds of blue and green on radars at the National Weather Service office in Wakefield.

At least that’s what’s believed to be causing the radar return.

As Wakefield meteorologist Mike Montefusco explained: “Obviously we’re not bug experts on our end, but there was a case like this in the Cleveland office last week where they did determine it was dragonflies. So that’s our running theory at this point.”

Wakefield started picking up the bug clutter Monday, from Richmond down into North Carolina, and tweeted about it.

Phillip Stepanian, an ecologist at the University of Notre Dame who specializes in interpreting the radar signatures of animals, says radar can recognize large swarms of winged creatures, especially as technology has improved.

For one thing, the individuals in a biomass aren’t shaped like raindrops. For another, they don’t fall to the ground like precipitation.

“But one of the problems is that while you have a good idea it’s insects, you don’t know if it’s butterflies or dragonflies or something else,” Stepanian said. “But when you have reports from people on the ground — and there have been tons of people reporting absolutely high numbers of dragonflies — suddenly this blob on the radar has an identity, and that sort of gets people excited.”

Montefusco, who’s been working in Wakefield for 13 years, has seen insect and bird signatures before.

“But this is a little more exaggerated,” he said. “What we’ve seen in the past couple of days here is pretty interesting. The volume of clutter evident on the radar — and not just our radar, multiple radars across the southeast are picking up the same signal — it’s kind of a curious phenomenon.”

So is the altitude.

“We were getting returns over 10,000 feet high,” Montefusco said. “Again, this is outside our area of expertise, but doesn’t seem like there’d be much reason for insects to be up that high. There’s just not much up there for them.”

It’s all about the ride, said Sally Entrekin, an aquatic entomologist at Virginia Tech. While it’s impossible to say if the dragonflies picked up on local radar are indeed local or just passing through, they’re all heading south ahead of winter, taking advantage of lofty winds that have recently shifted to blow that way.

"If they’re up that high, they’re on the move,” Entrekin said, searching for warmer places to lay eggs.

Dragonflies come in many species, though only about six types migrate, some for hundreds of miles. Apparently, conditions have been favorable enough this year to allow for a bumper crop of those kind.

A typical dragonfly lives about a year and spends most of that time as a nymph in water. As delicate-winged adults, they only last a month or less.

“But isn’t it great there’s so many this year?" Entrekin said. “They eat mosquitoes and other things that are pests for people. And they’re just beautiful, too.”

So how many dragonflies does it take to show up on a weather radar?



Stepanian only knew this for sure:

“A whole lot.”

Get our daily Headlines Newsletter

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Recommended for you

Load comments