Mayflies hatch all over Michigan

Earlier this month, residents in northeast Michigan may have spotted small specks of mayflies (also called “fish flies”) near the water or in their porch light.

Although the swarm has become smaller since then, more are likely to appear later in the summer.

Mayfly season typically occurs between June and August near freshwater. During this time, the insects hatch, fly, and mate within 48 hours before dying. As the weather warms, swarms have appeared across the state.

David Lowenstein is a consumer horticulture educator at Michigan State University with a background in entomology. He said the insects’ short lifespans mean they stay relatively close to water and that hatching times and swarm sizes can vary widely.

“You really have to be close to a stream or a lake (to see them),” he said. “A mile or a mile and a half can make the difference between experiencing a lot of fish flies or it being business as usual and you having no idea there are fish flies active in the area at all.”

Lowenstein said the trigger that causes mayflies to hatch is water temperature. Once the water temperature reaches 20 degrees Celsius, the insects begin to hatch and enter the adult stage of their life cycle.

According to the National Weather Service, water temperatures on the Great Lakes vary. While Lake Erie and Lake St. Clair have already recorded water temperatures of up to 22 degrees Celsius, parts of Lake Michigan and Lake Huron are still only 11 degrees Celsius.

Data from the National Oceanic and Atmospheric Administration (NOAA) shows that average water temperatures in these northern lakes tend to remain below the limit until July or August.

Nevertheless, temperatures in smaller bodies of water in northeastern counties such as Alcona, Oscoda and Iosco are already near or above the required temperature for mayfly hatching, and swarms are already being reported in southeastern Michigan.

Lowenstein said that while the insects may be a nuisance to some, in communities surrounded by water they are actually a good sign because they indicate good water quality. He said areas with high oxygen levels and less agricultural runoff tend to have higher mayfly populations, while areas polluted by agricultural runoff tend to have more algal blooms.

“It’s good to experience fish flies,” he said. “If you don’t like fish flies and live near a lake, turn off the lights on your porch at night and keep the windows closed, but otherwise, that’s just part of summer in Michigan and living near water. I think it’s worth trading a few days of insects that some find annoying for a sign that our waterways are doing quite well.”

This story was produced by the Michigan News Group Internship Program, a collaboration between WCMU Public Media and local newspapers in central and northern Michigan. The program’s goal is to train the next generation of journalists and combat the creation of news deserts in rural areas.