The life cycle of the mayfly is so vital to the aquatic ecosystem — especially in northwest Ohio and southeast Michigan — that it is one of the main indicators of freshwater health.
Most people think of the mayfly only at its worst — the annual rite of passage of spring into summer when the nightly cloud of the adult mayflies, or imago, are fluttering around outdoor house lights or clinging to the gas pumps under the service station lighting, making people grit their teeth as the insects fly into their hair or mouth or crunch under their feet.
Even though they are named for when the nymph’s winged metamorphosis typically comes out in May, they can emerge as early as April or even well into July and August, according to the Michigan State University Extension article in 2024.
GIVING LIGHT TO MAYFLIES• Mayflies are attracted to lights (phototaxis) because they are attracted to the moon; following moonlight is part of what helps them emerge from the lake en masse as they do.• Mayflies’ emergence is triggered by water temperature, oxygen levels, and light availability. The best predictor is when the Western Basin’s water temperature reaches 68 degrees at depth — meaning we cannot just look at water surface temperature, which is often a few degrees warmer than the bottom.• The most common are ephemeridae, flathead, and isonichydae, pictured, as well as baetidae, baetiscidae, and some others. The ones seen the most during the mass emergence are a species of burrowing mayfly, also in the Ephemeridae family.
And much like what triggers the walleye spawning run — a water temperature in the mid-40s Fahrenheit along with increasing daylight — the mayfly emerges when there is a streamlined temperature of 68 Fahrenheit from the sediments of the water to the surface…