Millions of fish flies coat southern Manitoba

Bug-beleaguered southern Manitoba are enduring yet another insect invasion — this time one of the worst infestations of fish flies seen in years.

Short-lived insect an indicator of healthier waterways

Fish flies typically live only a day or two in their adult, flying stage. ((CBC))
Bug-beleaguered southern Manitobans are enduring yet another insect invasion — this time one of the worst infestations of fish flies seen in years.

Plagues of cankerworms and mosquitoes seem to have subsided in most areas, but now fish flies are being seen in unusually high numbers in lake- and riverside communities across the province, including Winnipeg and the Lake Winnipeg cottage communities.

Fish flies — also known as sand flies, mayflies and shadflies — are winged aquatic insects about three centimetres long. They make brief, though messy, appearances in Manitoba every summer, hovering around lights and clinging to windows and walls; their flying, adult lifespan lasts less than two days — long enough to mate — then they die.

People in Gimli say the flies are the worst they've seen in five years, with deep piles of carcasses appearing along the beach and boardwalk.

"We're shovelling up garbage bags full of these things," said Braedan King, who cleans up the bodies of thousands of fish flies from Gimli's beaches and boardwalks each morning.

"It's disgusting. We might go through eight garbage bags."

Fish fly carcasses cover the ground in Gimli, Man. ((CBC))
Terry Galloway, an entomology professor at the University of Manitoba, said Winnipeg has also been inundated.

"We were driving down Pembina Highway and I had never seen so many in our part of the city at all," he said. "It's partly a function of the numbers, but it probably also has a little bit to do with the wind conditions."

Galloway said several possible explanations could be behind the plentiful flies, including stable water levels and the right temperatures.

Lake and river levels have been relatively stable for at least a year, so more of the insect's eggs have survived, Galloway said.

A fish fly takes a break on a CBC television camera. ((CBC) )
The greater numbers could also be a sign of healthier waterways. 

Fish fly eggs require oxygen on river and lake bottoms to survive until hatching, so increased populations could point to improved conditions, such as less algae.

"It is an indicator species of a less polluted ecosystem," said city entomologist Taz Stuart.

The fish fly infestation is good news for the fish that feed on them.

As for disgusted humans, Galloway said to take heart: We're almost through the peak of the infestation and they won't be around much longer.