Mayflies- A Sign of Good Times

June 9, 2002
by Laura Jones, a news release of the Ohio DNR

They are called many things (and a few of those names are polite): Canadian soldiers, June bugs, shadflies and a danged nuisance. The prolific and pesky family of aquatic insects known as mayflies may be the most sworn-at creatures in Ohio, but they're also clean-water barometers for our lakes and streams.

Bottom-dwelling insects for the first year or so of their lives, mayflies could never emerge in adulthood without clean, oxygen-rich sediment in the lakes and streams they call home.

About an inch in length, the mayfly can be identified by its elongated body and delicate, transparent wings. These harmless and attractive water lovers are found in nearly every major body of fresh water in the state, but are perhaps most closely associated with the western basin of Lake Erie, where they all but disappeared nearly 50 years ago.

"Mayflies were absent from Lake Erie for much of the 1950s and '60s when its waters were so much more polluted than they are today," said Randy Sanders, a wildlife biologist with the Ohio Department of Natural Resources. "They began reappearing in 1995, a sure sign that the lake was getting cleaner and healthier."

Along Ohio's North Coast, the species of mayflies called Hexagenia – by far the best known of 114 mayfly species in Ohio – are both a bane to shoreline residents and a boon to sport anglers who frequently try to emulate the fanciful bugs when tying artificial fishing lures.

As mayfly nymphs living under water, they breathe through gills located in their abdomens. During this aquatic phase, they shed their skins several times to accommodate their growing bodies.

Here’s a piece of trivia for bug lovers: mayflies are the only group of insects to have two life stages with wings: underwater during the nymph stage and as the adult mayfly. They are also the only insects that shed their skin after having wings.

Each June, like a scene from a horror film, millions of adult mayflies swarm from the lake's shallow waters and move inland for a short but spectacular shore leave. Mayflies mate in flight, after which the female flies back over the water and deposits as many as 8,000 eggs. There, her eggs sink into the sediment at the lake’s bottom. The entire process – from the time the mayfly nymph emerges from the water to molt, mate and die – takes only 24 to 72 hours.

Mayflies are a favorite delicacy for hungry Lake Erie fish, including the prized walleye, smallmouth bass and yellow perch. Referred to as the "lynchpin" species in the lake’s food chain, mayflies convert vegetation into palatable tidbits for fish and birds.

Biologists say there is a direct connection between the return of the mayfly after a 50-year absence and the resurgence in Lake Erie's walleye fishery. Along with bald eagles and walleyes, mayflies are a key indication of Lake Erie's overall good health.

About a dozen Canadian and American scientists are currently studying the lifecycle of Hexagenia in an effort to better understand the insects' total contribution to Lake Erie's complex ecosystem.

While their annual reproduction ritual is a nuisance for locals who must scrape swarming mayflies from windshields and shovel them off porches and roadways, it is a life-affirming sign for biologists who understand the insects' important role in Lake Erie's intricate food chain.

So, for lakeshore Ohioans who think the mayfly invasion is worse this year than last, here's some advice. Take a (careful) deep breath and think of it this way: the mayflies will be gone as suddenly as they appeared, but the clean water that gave them their start will be there for you and yours to enjoy for a long time to come.