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They may be late, but they have arrived!

'The timing of this annual event can be linked to seasonal temperature, so when we have cooler springs, shadfly emergence may be delayed'
Shad Flies cover a downtown flag on Main Street in North Bay Thursday morning. Photo by Chris Dawson/

The shadfly (mayfly) invasion was late for the Canada Day celebrations this year.  

Traditionally, the bugs come out of Lake Nipissing in droves in late June, many years causing challenges during Canada Day celebrations on the waterfront. 

This year, however, they just started to arrive in the downtown core this week.  

Weather may be the determining factor.

According to Helicopters Canada, the ice left Lake Nipissing officially on Monday, May 14th, 

Records indicate that is the fourth latest all-time ice-free date since records have been kept.  

Norm Dokis, Resource Liaison Specialist for the MNRF in North Bay, says the shadflies arrive when the water gets to the right temperature.  

“When the water reaches 20 degrees Celsius, juvenile shadflies (nymphs) emerge from the water and head to the shore to moult and find mates,” said Dokis. 

“The timing of this annual event can be linked to seasonal temperature, so when we have cooler springs, shadfly emergence may be delayed.” 

While many find the shadfly phenomenon disgusting, Dokis insists research shows they are an important part of Lake Nipissing’s environment.  

“They sequester nutrients from the lake (such as phosphorous and nitrogen) and transport these to shoreline environments during their emergence, which is where some of their ‘fishy’ smell may come from,” he said.  

“Shadflies are an indicator of ecosystem health. Their presence on Lake Nipissing is good as they support a number of ecological processes, such as nutrient cycling and providing a food resource to other aquatic species.” 

Dokis reminds local businesses that the shads are attracted to light.  

“Shad Flies use light to navigate through the air- thus, they are attracted to artificial lighting,” said Dokis.  

“Reducing the use of outdoor lighting during peak shadfly season may reduce the accumulation of these insects at private dwellings or other buildings.”  

While they are a nuisance, the major complaint most people talk about is the smell.  

“At the levels we normally experience, the major complaint that people can muster against them is that they find them annoying and somewhat smelly,” he said. 

And while annoying, shadflies don't bite and only live 24 hours.

Chris Dawson

About the Author: Chris Dawson

Chris Dawson has been with since 2004. He has provided up-to-the-minute sports coverage and has become a key member of the BayToday news team.
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