The Mayflies are coming – time to celebrate!

The annual Mayfly hatch not only tells us what season it is, but also confirms the quality of the water bodies from which they come.

Mayflies have an interesting life cycle and, depending on the species, live for only days or in some cases, mere hours. Photo credit: Todd Marsee, Michigan Sea Grant.
Mayflies have an interesting life cycle and, depending on the species, live for only days or in some cases, mere hours. Photo credit: Todd Marsee, Michigan Sea Grant.

It’s summer, so it’s time for the mayfly hatch! There are hundreds of species of mayflies (also commonly referred to as fish flies) in North America, representing a number of Families in the Order Ephemeroptera. Ephemeroptera comes from the Greek word for “short-lived” (as in “ephemeral”), and it’s a good name because as winged adults, mayflies only live a few days. The most widespread burrowing mayfly species in the Great Lakes is Hexagenia limbata, the Giant Mayfly.

Mayflies have a very interesting life cycle. They are the only insect to have two “adult” molts, and begin life as eggs laid on the surface of the water that sink to the bottom. The aquatic nymphs of mayflies are called naiads, and creep around rocks and vegetation. After months or years (depending on the species), they float to the surface and molt to a winged, but sexually immature, sub-adult. Often within hours, another molt occurs and the final stage emerges—the winged, reproductive adults, which possess only vestigial mouth parts and cannot eat or drink and, depending on the species, live for only days or, in some cases, mere hours.

Mayfly swarm on Doppler radar over wester Lake Erie image.One of the most obvious characteristics of the adults is their large numbers. They can emerge in huge numbers from a body of water. So huge, in fact, that their swarms can be seen on Doppler radar! This image is from June 14 showing a mayfly swarm over western Lake Erie, pushed ashore in Monroe County by an easterly breeze. Once ashore, mayflies tend to sit on upright objects and can completely cover the surfaces of posts, sheds, and light poles. At night, they are attracted to lights.

Some people think of mayfly hatches as a nuisance, and they can be a bit annoying when they are swarming. But mayflies are a good thing. They are rarely found in degraded bodies of water because their external gills in the nymph stage are very vulnerable to silting and pollution. Mayflies are, therefore, used as an indicator species when testing for environmental quality, and their presence reflects the good quality of the habitat from which they hatched. Michigan State University Extension and Michigan Sea Grant—through the Great Lakes Education Program, 4-H Great Lakes & Natural Resources Camp and Summer Discovery Cruises—focus on indicator species to highlight Great Lakes Literacy Principle #6—“the Great Lakes and humans in their watersheds are inextricably interconnected.” Mayflies are useful indicators because they are highly visible, relatively easy to sample, and provide "real proof" that lake restoration has been effective.

Mayflies are also the angler’s friend. Both immature stages and winged adult stages are favorite foods for fish such as trout, bass, yellow perch and many others, as well as smaller aquatic predators in the food chain. When appearing in swarms, mayflies usually cause fish to swarm as well, andBay-Rama Fish Fly Festival banner image anglers create fishing flies to resemble adult mayflies. Some coastal communities have even adopted the mayfly as a welcome harbinger of summer, and feature them in annual festivals such as the Bay-Rama Fish Fly Festival in New Baltimore, on the shores of Lake St. Clair.

As if more proof was needed to establish the “goodness” of mayflies, teachers find the mayfly an interesting topic for classroom instruction, and the TEACH Great Lakes curriculum includes the excellent “Mayflies on the Move” lesson for middle school students. The mayflies of Lake Erie are so popular that they enjoy their own official website—The Mayflies of Lake Erie!–-and even poets wax eloquent about the beloved mayfly, as in Douglas Florian’s “The Mayfly.” So this summer, enjoy the mayfly hatch—it’s a good thing!

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