Hot weather, rain invite those swarms of tiny flies, UdeM entomologist explains

These small, slender-bodied flies are called midges, and July is their prime season.

These small, slender-bodied flies are called midges, and July is their prime season

According to Etienne Normandin, an entomologist at Animature and at Université de Montréal, especially hot weather like we've experienced this year can mean more midges. (submitted by Gilles Arbour)

It's not uncommon to walk through swarms of tiny flies while strolling on the streets of Montreal on a hot July day — or to get one of those bugs stuck in your eye.

The small, slender-bodied flies are called midges, and July is their prime season.

According to Université de Montréal entomologist Étienne Normandin, especially hot weather like we've experienced this summer can mean more midges.

"For insects, when you have more heat, the metabolism is going to go faster," Normandin said.

One type of midge common to Quebec begins its life as larva at the bottom of a lake. When the weather is hot, the top few metres of the lake are warmer, causing the water to move around.

"Then the soil at the bottom gets lighter," Normandin said. "It can force the emergence of larvae."

According to Étienne​ Normandin, a Université de Montréal entomologist, especially hot weather like Montreal has experienced this year can mean more midges. (Claire Loewen/CBC)

But even though the heat can bring on more midges and help them reproduce more quickly, it can also shorten their already ephemeral lives — they normally live for just two or three days at the adult stage, Normandin says.

The heat hasn't gone away, but will the rain we've seen in Quebec over the past few days offer a respite from these swarms? Likely not, Normandin says.

Since rain is typically colder than the body of a lake, it also can cause movement in the water that has the same result as the heat.

What's happening inside the swarm?

When you walk through a swarm of flies, you might just be interrupting a round of speed dating.

"They're kind of mating," Normandin said.

The females are at the centre, and the males fly around them, fighting for their attention.

"They catch little prey, little insects, and when they find a female, they give their gifts to the female to be able to mate with her."

Although these midges are harmless to humans, one invasive species is compromising the biodiversity of some lakes.

The chaoborus, more commonly known as the glassworm, lives in the top layer of a lake and feeds on zooplankton, he says, depriving other native insects and minnows of their main food source.

With files from CBC Homerun