In 1495, the artist Albrecht Dürer made a famous engraving of the Holy Family that included a mayfly. Dürer meant it to suggest a link between heaven and earth, perhaps because of their brief 48 hours of life once hatched. In Michigan, swarms of mayflies, sometimes known as fish flies due to their fishy smells, can often signal the beginning of summer.
“Mayflies are cold-blooded, so what that means is that the higher the temperature, the faster they grow,” Richard Merritt, a former entomology professor at Michigan State University, told Stateside.
Up close, the mayfly is a light insect with very long legs that allow them to glide over the water’s surface without sinking. As they glide, they drop their eggs and take off without drowning — unless a fish grabs them.
“Which is often the case, especially in rivers like the Au Sable River in Michigan, and some of the premiere trout streams,” Merritt explained.
Once the mayfly egg reaches the lake floor, the larvae will begin searching for the perfect place to call home.
“They will search for a place in the sediments where… they are able to dig in the mud and create a J-shaped tube where they live in that entire time,” he said.
As the larvae settle into the sediment, they rapidly move their oversized gills to draw in particles from the surrounding floor, filtering them for food. The nymphs feed on these particles until they reach adulthood over the course of a year.
Once Michigan enters spring and temperatures warm up enough for the mayfly to reach adulthood, they swim away from their nests at the bottom of the lake. As they emerge from the water, the mayflies will intentionally not feed in order to save time and energy.
“Their whole sole purpose in life once they become an adult is to find a mate,” Merritt said “And they’ll fly around in these swarms, and the females fly through the swarm. And the male will grab them and copulate with them.”
All that flying forces the mayflies to have to rest in between mates, which is why you might often see many of them resting on houses or cars.
“They have to rest because they’re not going to live long, so they need to accumulate as much energy and save it for their mating and laying of eggs for the females before they die,” he added.
The entire process, Merritt said, lasts about two days. These days, it’s safe to say we can count on mayflies showing up year after year. But back in the 1960s, the pesky little insects — known to occasionally cause motor vehicle accidents — virtually disappeared from Lake Erie.
“All of a sudden, mayflies started disappearing, and people wondered why they weren't coming off,” Merritt said. “Because mayflies are a good sign of clean water, and they don’t breed in polluted water.”
Further investigations into the mayfly’s disappearance revealed that Lake Erie was becoming polluted by industrial waste being dumped into the water. Merritt said that discovery is part of what pushed the government to form the Environmental Protection Agency.
“A large part of it was based on mayflies. They knew something was wrong with the water, and so the EPA was formed to safeguard streams, lakes, and ponds, and everything from being polluted.”
According to a 2000 issue of Great Lakes Research Review, mayflies suddenly disappeared from Lake Erie in 1953 and remained absent for nearly 40 years, only reappearing in the 1990s. A 1968 Time article blamed smog for depleting the lake’s oxygen levels, making it unable to sustain life. Just a year later, President Richard Nixon established the Council on Environmental Quality, and soon after, Congress passed the National Environmental Policy Act.
So far this year, the mayflies haven’t yet appeared, which Merritt said, shouldn’t be a cause for concern.
“Normally there would be more mayflies coming off as adults, but the water temperature this past year, especially in the spring, has been cold and so it delays the hatching of this mass emergence of adults.”
Merritt predicts over the next couple of weeks, temperatures on the Great Lakes will reach the ideal point for the mayflies to come out of their year-long slumber.
