Toronto’s annual spring swarms of midges are back, but while the clouds of tiny flies may seem alarming, an expert says these insects play a crucial ecological role. Their presence means local freshwater ecosystems are functioning well.
Midges, which resemble mosquitoes but don’t bite, emerge each spring from bodies of water such as Lake Ontario and nearby ponds and rivers.
“They’re related to mosquitoes, but unlike mosquitoes, midges don’t bite. They will emerge from water in the springtime, and they form clouds that people probably have walked or bicycled through. And those clouds of flies usually last for a couple of days, but the adult flies don’t actually feed, and they only emerge for a few days at a time, and then they die,” Micah Freedman, an assistant professor in the Department of Ecology and Evolutionary Biology at the University of Toronto, told Now Toronto.
The midges seen swarming around Toronto at this time of year spent the fall and winter as larvae at the bottom of the lake.
As temperatures rise in April and May, they complete their development and emerge as adult midges. Once in the air, they take part in a mating ritual.
“Those big swarms you see are mostly male flies, and it’s part of a mating display that they do. The males will pick a certain spot, usually a couple of feet above the ground, and fly in clouds. And then females are attracted to those swarms of flies and will go to find a mate there,” Freedman said.
INDICATORS OF A HEALTHY ECOSYSTEM
While walking or biking through a swarm might be unpleasant to most, Freedman said it’s a good sign for the city’s aquatic health.
“Midges are indicators of water quality, and the fact that you see a lot of midge flies down along the Toronto waterfront is an indication that those waters aren’t terribly polluted, since they wouldn’t survive if there were tons of pesticide residues in the water or other things that would reduce water quality,” Freedman said.
“It’s maybe a small consolation for the people who are walking through a big cloud of them, but it’s at least an indication that the water quality along the lakefront is at least decent.”
Midges are also food for a wide range of species, and play a key role in decomposing plant material and algae in bodies of water.
“You can think of them similarly to caterpillars for a butterfly. They go through a complete metamorphosis where they totally transform, and that immature stage develops underwater, and they feed on decaying plant material and algae. They are sort of decomposers of this material that would otherwise accumulate in water bodies.”
“The other reason that they’re really important is that they’re a big first step in aquatic food chains. They take up biomass from this decline decaying plant material, but then they become food for a lot of other organisms like fish, salamanders, and then when they emerge as adult flies, there are a lot of other species, like birds and dragonflies that feed on them,” Freedman continued to say.
HOW LONG WILL THEY STAY?
Midge activity is most noticeable in the early spring, when warm temperatures trigger synchronized swarming.
By the time summer arrives, the swarms are less concentrated and harder to spot, though individual midges may still be present in smaller numbers throughout the season.
Freedman, who recently moved to Toronto, estimated the swarming period typically lasts a few weeks, peaking in late April and early May.
“It’s just these big swarms that are a springtime phenomenon,” he said.
TIPS FOR AVOIDING THE SWARMS
Freedman advised to wear a mask to avoid breathing them in, and also noted that checking the breeze before going near the water will help.
“My best advice would be — if you do want to go down by the water this time of year, any time that there’s a small breeze that can help dissipate the big clouds of them,” he explained.
He also recommends wearing sunglasses while biking or walking near the lake.
Midges are more active during calm, warm evenings, so visiting earlier in the day will also help, according to Freedman.
Though brief and a little bothersome, Toronto’s springtime ridges are doing exactly what they’re meant to do, and offering a sign that the city’s waters are still alive and well.
