16-07-2025
What the pesky swarm of mayflies say about the health of our lakes
They appear in massive, pesky, swarms striking an unusual reaction from anyone living near the water.
But before swatting them away or complaining about their creepy appearance and substantial presence it's worth asking: What are these insects good for?
Despite their name, mayflies or shadflies, these critters typically appear in late spring and summer especially around freshwater lakes and rivers. They gather in large numbers near cottages, hanging in clusters from street lights and swarming around boardwalks.
Though short-lived, their lives often begin underwater where they play an essential role in our local ecosystems.
According to the National Wildlife Federation, Mayfly larvae, spend up to a year beneath the water's surface, feeding on yummy plants and organic debris. They serve as food for fish, amphibians, and birds alike.
Mayflies
Pesky mayflies swarm Lake Simcoe. (Lake Simcoe Region Conservation Authority - LSRCA)
But surprisingly enough their value doesn't stop there.
'Mayflies are a natural bioindicator,' says the Lake Simcoe Region Conservation Authority in Newmarket. 'They thrive only in clean, oxygen-rich water. When we see them emerge in large numbers, we know the water is healthy.'
Lake Simcoe, specifically, sees massive mayfly emergences each year. Believe it or not, this swarm is actually an encouraging sign according to conservationists out of Newmarket.
These large-winged insects even inspired the name of the authority's research vessel.
'Their scientific name is the namesake of our research boat and reflects our ultimate goal of a healthy Lake Simcoe,' shared the local conservation authority. While they may seem like a nuisance to some, mayflies tell an important story about the water we swim in.
These oddly large bugs aren't just a summertime spectacle, they're a reminder that the ecosystem is functioning properly.
So the next time you are at the cottage or enjoying a day on the lake and you stumble across this odd critter that may cloud your headlights or cover your dock, just remember... their presence is actually a positive sign.
