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This summer, I had my own question: Why am I seeing so many dragonflies in Pittsburgh? In fact, recently when I was in the middle of the city, sitting in traffic, two were mating on my car windshield. I don’t remember seeing anything like it before.
LISTEN: What’s Up With All These Dragonflies?
So I consulted an expert: Dennis McNair, a retired biology professor from the University of Pittsburgh at Johnstown. He has studied a restored wetland in Bedford County for 20 years, where he’s documented over 60 species of dragonflies and smaller, more delicate damselflies. According to McNair, there are a lot of answers to my question.
“One of them is: When people start seeing things, no matter what it is—you know, smart cars or whatever—once you’ve seen one, you start seeing others,” he says.
OK. Sure. But he also said there could be some science behind it.
“The other thing is: This was a droughty summer. The dragonflies maybe had warmer water they were developing in.”
Now we’re getting somewhere. McNair explains to me that dragonflies actually spend most of their lives in the water in the larval stage. They even overwinter in the water—only leaving to mate. Dragonflies eat mosquitoes and other bugs, which have also done well this summer. So it’s possible the early spring and warm summer caused more of them to take flight. Maybe.
McNair says it’s not exactly surprising to see dragonflies in Pittsburgh, considering it’s surrounded by three major rivers. Plus, there are plenty of other places where dragonflies like to hang out.
“If you have a backyard pond, dragonflies will eventually find it and live there, as long as it’s six or eight feet across.”
The water just has to have some kind of surface where they can lay their eggs. He says different species have their own habitat needs. Some are pretty tough. They can even live on acid mine drainage treatment ponds.
Because I was in motion most times I saw the dragonflies, and they are swift fliers, I didn’t get a chance to snap photos or ID any of them. But McNair says the ones I’ve been spotting in parking lots or along streets could be wandering gliders, so named, he says, because “they wander around a lot.”
He says there are other possibilities. Meadowhawks also come out this time of year. They’re little and red and they “hawk” after their insect prey—capturing them over vegetation.
Some dragonflies even migrate.
“They will migrate in the fall, kind of like birds, especially along the coast,” McNair says. “They will aggregate in large numbers someplace, and then they’ll move as a group—sometimes hundreds of miles.”
McNair says scientists are still trying to figure out exactly where they go. And researchers are also starting to look at how climate change is affecting dragonflies. For instance, over the last several years, McNair says he’s seeing greater numbers of a couple species that are common in the south, but usually rare at his Bedford County location.
“Carolina saddlebags and mocha emeralds are usually found down in Virginia and the Carolinas,” he says. “But it will take many more years and many more observers before we know for sure that they’ve shifted their range.”
Researchers are more concerned with organisms that carry disease, like mosquitoes and ticks—which are moving their range north as a result of climate change.
McNair has loved insects since he was 10 years old, and says he remains a boy at heart. He’s attracted to dragonflies for the same reason they’re featured in paintings, stained glass and poetry—they’re beautiful.
Dragonflies are in the Odonata group, if you want to be technical about it. But if you want to get lyrical, their non-scientific, common names are just as intricate as their lacy wings: Azure bluet, citrine forktail, fawn darner.
“One of the reasons that they have a lay name like darner, or sewing needles, is if you watch the females, they’ll go along the surface of the water, and many species, they’ll stick their abdomen down into the water like an old sewing machine,” McNair says. “My grandmother told me when I was a little boy that if I told a lie, dragonflies would come and darn my mouth shut.”
While that’s a terrifying thought, McNair says there’s nothing to worry about. That long, slender abdomen doesn’t sting—though dragonflies will mimic bees or wasps if you try to hold onto one.
I keep McNair far longer than I should for my one little question. I said I’d only take up an hour of his time. But he seems happy to show me his framed, original drawings from Ed Lam’s book, Damselflies of the Northeast, and generously share one fascinating dragonfly fact after another.
Here are a few more for you:
There are about 170 different dragonfly and damselfly species in Pennsylvania, and around 450 in North America.
In the larval stage, dragonflies and damselflies have a large, claw-like lower lip. It juts out from their faces—almost like an elbowed arm, and they use it to catch their food. Then it folds back up against their mouths so they can eat. McNair says they look like monsters. They lose the lip as adults.
Adult dragonflies hunt on the wing, nabbing other insects by forming a basket with their legs. They’re quick and efficient. McNair says adult dragonflies are more than 90 percent successful in capturing their prey. Most predators are considered successful if they kill 20 percent of the animals they go for. He tells me a large dragonfly can eat up to 1,000 mosquitoes in a day.
A dragonfly’s head is all eyes. With them, they can see 280 degrees—and backwards— whereas humans can only see 180 degrees with our peripheral vision. McNair says old movies are shown at a projection speed of 55 still pictures per second and humans perceive it as a fluid, moving image. For dragonflies, that speed is super slow motion. Their “flicker fusion” is higher because of pigments in their eyes. That’s why they are hard to catch in a net, and can dart and zig-zag around at a pretty high speed.
This story is part of our partnership with iSeeChange—an online experiment in citizen science that let’s anyone investigate how weather and climate change is affecting the environment. Find out more at iseechange.org or check out NASA’s iSeeChange Tracker app on iTunes. Photo (top): A blue darter dragonfly. Credit: HdG Photography via Flickr