Communities along the Great Lakes are preparing for the annual mayfly season, but water temperatures may not be warm enough quite yet for the fishflies to produce massive swarms.
“The timing of mayfly emergence from sediments is based on the water temperature. Mayflies emerge after the water temperature at depth reaches 20 degrees Celsius (68 degrees Fahrenheit),” Sea Grant Michigan, a Great Lakes research program said. “In the western Lake Erie basin and Lake St. Clair, water is shallow enough that the water temperature at the surface is only a few degrees different from the temperature at depth.”
Around mid- to late June is when mayflies typically emerge to breed.
As of June 10, Great Lakes’ surface water temperatures range from the 40s to upper 50s, with Lake Erie the warmest, according to National Oceanic Atmospheric Administration Great Lakes observations.
Lake Erie — the shallowest of the lakes — saw an average water temperature of 61 degrees according to Seatemperature.com. NOAA graphs shows the western end of the lake at or just above 60 degrees while the eastern end is cooler.
While water temperatures may be cool enough to keep massive swarms at bay a little longer, Toledo, Ohio-based meteorologist Chris Vickers this week said the bugs have been spotted already.
“HEADS UP!,” the WTOL weatherman posted on Facebook. “Swarms of mayflies moving inland off Lake Erie. I’ve spotted the first heavy mayfly infestation on Doppler Radar.”
While many residents plan to avoid mayflies some revel in their unique behavior. For instance, In Dundee, Michigan, the 24th annual Mayfly Music Festival will take place on June 20-21 at Wolverine Park. There will be music, fireworks food and (likely) mayflies.
Here’s how to reduce swarms of the aquatic species:
How can I keep mayflies away from my house?
While mayflies are not harmful, they can be annoying to waterfront community residents.
If you want to keep mayflies away, here are some tips from pestworld.org:
Turn off outdoor lighting. The insects are attracted to bright lights.
Replace white incandescent fluorescent bulbs with yellow bulbs.
Ensure all doors and widows are properly screened and secured, and seal holes and cracks.
If dead mayflies collect near your house or yard, Orkin, a pest control company, suggests using a vacuum with a HEPA filter (a high efficiency particulate air filter) to quickly remove them, or to use a broom and dustpan.
Why does my outdoor lighting attract mayflies?
Outdoor lighting often attracts bugs because they are drawn to the light’s UV output, according to Dodson Pest Control.
“Insects generally see three colors of light, ultraviolet (UV), blue and green. Bright white or bluish lights (mercury vapor, white incandescent and white florescent) are the most attractive to insects,” the pest company said, “Yellowish, pinkish, or orange (sodium vapor, halogen, dichroic yellow) are the least attractive to most insects.”
What are the Great Lakes’ water temperatures?
Because mayfly season is dependent on water temperature, here are the average water temperatures of the Great Lakes, as of June 10, according to Seatemperature.com:
Lake Michigan: 49.5 degrees
Lake Superior: 40.7 degrees
Lake Ontario: 53.2 degrees
As temperatures climb, residents can monitor water temperatures of the Great Lakes online.
What is a mayfly?
Mayflies are small (quarter-sized or larger) aquatic insects. They spend most of their life cycle in water then, as adults, they leave to mate, according to the National Wildlife Federation.
There are more than 600 different mayfly species in the U.S., with over 100 in Michigan.
Mayflies have four translucent wings (similar to a dragonfly), large eyes, a long segmented abdomen, two or three prominent tails, six legs and two antennae.
Adult mayflies don’t develop functional mouths, so don’t even feed during their brief lifespan, MSU Extension says. Though adult mayflies do not eat, but nymphs eat detritus, other plant material and some insects, the NWF said.
What it the lifespan of a mayfly?
“The mayfly crams its adulthood into a brief period. Within 48 hours, they develop wings, fly toward land, mate and die. If you reside near one of the Great Lakes, your garden or home and community may briefly be overwhelmed with up to 88 billion mayflies,” according to Michigan State University’s Extension.
Once they emerge from water, adult male mayflies can live for one to two days, according to the International Fund for Animal Welfare.
Female mayflies are said to only live for a mere five minutes.
“Although there are several species among many groups of insects that exist for only a few days as adults, the shortest adult reproductive life belongs to the female of the mayfly Dolania americana (Ephemeroptera) which lives for less than five minutes after its final molt,” according to the University of Florida’s Book of Insect Records.
More: When will the mayflies arrive? What to know
What’s the difference between a mayfly and a midge?
Mayflies and midges are look-a-likes due to their shared stringy, flappy and aquatic nature. To make the distinction, midges are often smaller, according to the Northeast Ohio Regional Sewer District.
Are mayflies dangerous?
No, mayflies are not considered dangerous. They can’t bite or sting, according to Birds&Blooms.
Seeing mayflies is a sign of a healthy environment, because they lay eggs in clean water.
“Mayflies are highly sensitive to pollution and other changes in their environment,” Stroud Water Research Center said. “When they are missing or few in number, it is a warning that a stream isn’t healthy enough for mayflies to live there.”
Contact Sarah Moore @ smoore@lsj.com
This article originally appeared on Lansing State Journal: Michigan mayflies 2025: Great Lakes near right temps for fishfly swarms