Experts predict an excellent year for dragonflies

Eastern pondhawk dragonfly Photo by David Byron Keener/Shutterstock

Ontario cottagers who love dragonflies (and hate mosquitoes) have good news. Thanks to a late spring and a large supply of winged prey, veteran dragonfly watcher Bob Bowles is predicting an “excellent year” for lovers of the voracious, jewel-like predators.

Dragonflies were slow to launch in central and northern parts of the province this spring. Blame “the impact of a late spring, but also an early winter in 2018,” says Shannon McCauley, an assistant professor in biology at the University of Toronto. “Most of the dragonflies and a large fraction of damselflies overwinter in the water, with a fair amount of growth and development in the fall. Winter came early, so they didn’t get that development.”

The result is a compressed season, with spring-emerging dragonflies showing up late to the party and being joined by their summer cousins. Southern areas have already reported good dragonfly numbers. For the rest of Ontario, “we won’t be disappointed by mid-July. There will be lots of dragonflies,” predicts Bowles, who leads dragonfly counts on Pelee Island, the Minesing Wetland, and the Carden Alvar. Thanks to healthy numbers of mosquitoes and biting flies, dragonflies “will certainly have lots to eat.”

Dragonflies (and their associates, damselflies) are long-term evolutionary survivors. Almost 300 million years ago they took flight among the first winged insects. Some ancient species—benefiting from oxygen levels much higher than we’re breathing today—became giants with 70 cm wingspans. Today’s downsized dragonflies still do impressive things, including the green darner’s 1,450 km migration from the Gulf of Mexico to Canada. A subsequent generation does the return trip in autumn.

And in an era when other insects seem to be declining, the odonates—dragonflies and damselflies—are holding their own, more or less. Based on more than 20 years of counts on the Carden Plain, “I haven’t been able to establish a trend,” Bowles says. Unlike other insects that rely on limited food sources, “dragonflies are very adaptable. They’ll eat almost anything they can get into their jaws.”

But they’re not immune to climate change. In both British Columbia and Ontario, southern species seem to be moving north, and a warming climate could be part of the push. In the west, the California spreadwing has appeared in the southern Okanagan, while the twelve-spotted skimmer is appearing in the Kootenay and Columbia Valleys.

In Ontario, the bright-green or electric-blue eastern pondhawk seems more common, adds McCauley. The southern species “may have the genetic capacity to deal with higher temperatures,” she adds. Meanwhile, northern species such as the dot-tailed whiteface “seem to be more negatively affected.”

The odonates’ ultimate fate is bound up with wetlands and water quality, adds Bowles. Dragonflies and damselflies spend weeks or months as nymphs in the aquatic environment before they metamorphose into their winged stage. If climate change reduces wetlands, fewer dragonflies will be around to control biting insects. Pollution, including road salt and other contaminants, also affects the glistening flyers.

To keep dragonflies in our skies—and their cool names in the lexicon—“what we really need to do,” says Bowles, “is protect our water systems.”

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