Why Do Dragonflies Swarm?

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A dragonfly hovers among the reeds in France. (Christopher Furlong/Getty Images)
A dragonfly hovers among the reeds in France. (Christopher Furlong/Getty Images)

Christine Goforth calls herself the Dragonfly Woman, and for good reason.

The aquatic insect expert doesn’t just study solo dragonflies. She studies massive swarms of dragonflies that form when large groups of the colorful, aerial insects pause their migration to feed.

“Dragonfly swarms are big groups of dragonflies that are typically feeding on little prey insects,” says Goforth, head of citizen science at the North Carolina Museum of Natural Sciences. “So you can get anywhere from a dozen to millions or even billions of dragonflies flying together in these big groups.”

She’s searching for the root of this behavior through a study called The Dragonfly Swarm Project.

Last week, dragonfly swarms were spotted in Indiana, Ohio and Pennsylvania.

These swarms are so large they’re showing up on weather radars, which Goforth says isn’t unusual for these clusters of creatures.

Interview Highlights

On what causes dragonfly swarms
“This is the season of the year where the dragonflies are starting to migrate so the migratory species are starting to move from the more northern parts of North America southward. And so you have a whole lot of dragonflies that are on the move right now. And every time they stop flying they need to eat. And so they form these big groups wherever there's a lot of little insects in a local area to feed on. And that's why you're starting to get the swarms. They do this pretty much every fall. They can do it throughout the year but you see a lot more of them now than you would earlier in the year.

“The data that I've collected through my Dragonfly Swarm Project suggests that disturbances play a really important role in this behavior so that anytime you get fires or floods or big storms or even people mowing their lawns is enough to kind of kick up a bunch of little insects that the dragonflies will take advantage of.”

On why she loves dragonflies
“For me, it's that they look so beautiful and delicate but they're so impressive. I mean they are amazing predators. They can eat all kinds of giant things. They've been known to eat birds, like hummingbirds. Some species have been documented catching and eating hummingbirds. And I think anytime you get an insect that's big enough to turn the tides on birds, that's really pretty cool.”

On what she hopes to learn from The Dragonfly Swarm Project
“I'm hoping to learn several different things. I want to know where the behavior forms in the first place, how that swarming pattern occurs, what are they doing, why are they doing it and how it benefits our environment.”

On the best dragonfly swarm she’s ever seen
“I think the best swarm I've ever seen was the very first one that got me interested in this behavior in the first place. I was doing aquatic work in Arizona and was around a pond that didn't have any vegetation. So, we really never saw dragonflies. But one day my co-worker and I showed up and there were hundreds and hundreds of dragonflies there flying in a big swarm. And I got really excited about that, which is why I have my project in the first place.”

On whether climate change plays a role in the swarms
“It's possible that climate change is related but it's hard to say whether something is being impacted by climate change without a very large dataset. I think it's too early to say. But with a recent hurricane that came through, it's likely that the increase of rain, any sort of localized flooding increases the number of mosquitoes and other small insects. And the dragonflies are flying in and taking care of that while they're on the move southward.”

Lynn Menegon produced and edited this interview for broadcast with Todd MundtAllison Hagan adapted it for the web.

This segment aired on September 17, 2019.

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