Ask Sam: Is Global Warming Good For Dragonflies?

Aug 9, 2019

This guy is totally going to take over the world once we're gone.
Credit Flickr Creative Commons | dotun55

  Every other Friday on Morning Edition NHPR’s Sam Evans-Brown tracks down answers to questions about the environment and outdoors for our listeners in a segment we call “Ask Sam.”

Rich from Hudson, NH asks: “I’ve noticed that last summer I noticed an awful lot of dragonflies in my neighborhood. And they were beautiful and they were much larger. I really liked it, and I wonder if this has something to do with the global warming that we’re experiencing?”

I’m going to cut to the chase on this one, Rich. I put your question to noted dragonfly expert, New Hampshire Audubon’s Pam Hunt, and the answer she gave me was “No.”

But don’t stop reading! I promise this is interesting.

Pam says that what she believes you most likely witnessed a swarm. It’s a poorly understood phenomenon, but it tends to occur in August and into September, and tends to be larger dragonfly species, mosaic darners and emeralds.  

“It’s usually over people’s yard or on open hillsides,” says Hunt “You can have dozens or more of these large, often subtly beautiful, black dragonflies with green and blue spots on them, swarming around catching flying ants or usually something like that which we don’t necessarily see.”

How do they know to where and when congregate? We have no idea. “How they find individual ant hatches in people’s yards is beyond our knowledge,” she explains.

There was a brief-lived citizen science project trying to document these swarms, run by an entomologist at the North Carolina Museum of Natural Sciences, but it hasn’t been updated since 2012. So, the mystery lives on.

We Rarely Count Bugs

How can we so easily dismiss the explanation that last year a particularly big year for dragonflies? 

An article in the Washington Post cites a bunch of anecdotal evidence to claim that this was the case, but Bryan Pfiefer, president of the Dragonfly Society of the Americas wrote in with a point-by-point rebuttal of the article

In an email to me, Pfiefer wrote “We don’t really measure year-to-year status of insects that have been around 300 million years or more. Sure, there are some bigger trends. But there’s really no reliable, broad data on whether it’s a "good year" or not for dragonflies.”

In other words, is it possible that last year was a big year? Sure. But we have no way of knowing. And given Rich’s description (big dragonflies, during August) a much more likely explanation is a swarm. 

This does bring up another, deeper quandary, however. The fact that we don’t bother to count bug populations from year-to-year means that we really don’t have a good idea of what’s going on with most insect species ever. This is particularly a problem because the signs we’re getting few long-term data sets that exist ain’t good

Ultimately, the real answer we can give to Rich’s question is a shrug. 

But Think Big Picture

One thing that’s worth remembering is that dragonflies have been around for a very, very long time. Their lineage goes all the way back to before the dinosaurs, and back then they were the size of a seagull

There may be exceptions: species that are cold adapted, or specialized to live in dry places, spending their pre-flying stages in water bodies that occasionally dry up. But there’s little reason to think that a warmer world would be bad for dragonflies in general. 

“Because they’re ectotherms, temperature is great… they can grow faster,” says Hunt.  

Of the population trends that we have observed, the pattern is one that repeats itself across all living things in the Anthropocene, generalist species are doing relatively well and specialists are declining

Specialists struggle not so much because of climate change, but “because they live in very specific habitats like bogs,” explains Melissa Sanchez Herrera, a dragonfly researcher who’s wrapping up a PhD at Rutgers, “These habitats may be in danger because of construction or urbanization.” 

Final Thought: Dragonflies Are So Cool

If I really had to guess what the root of Rich’s question was, I’d say that it was simply marveling at how amazing dragonflies are. 

Put another way: “I think dragonflies are very charismatic insects,” says Sanchez Herrera. 

They’re precision predators, with nearly 360 degree vision, take advantage of incredibly complicated flight physics, and studies have shown that they capture their intended prey 95 percent of the time. As nymphs they’re just as nifty, thanks to jaws that shoot forward to catch their prey, and they also can move by shooting a stream of water out of their body, like a little jet boat. 

Whether there are more of them or not, they’re likely to be around after we’re gone, so they’re worth paying attention to. 

“We can learn so many things about how to deal with our current change in our world,” says Sanchez Herrera, “They have been very resilient across evolutionary time.”

Sam Evans-Brown, is host of NHPR’s Outside/In which you can subscribe to where-ever you get your podcasts. If you’d like to submit a question you can record it as a voice memo on your smartphone and send it to oustidein@nhpr.org, OR call the hotline, 1-844-GO-OTTER, OR submit it here.

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