What I knew about mayflies: They’re called mayflies and they molt. I could’ve put my knowledge in a thimble and had room for War and Peace.
What I thought about mayflies: They’re creepy looking, and the exoskeletons they shed are even creepier. I could’ve imagined them starring in a B movie titled, Return of the Giant Mayflies.
Then in June my almost-ten-year-old granddaughter asked, “Why are they called mayflies? I never see them until June.”
“I’m not sure,” I said. “We’re going to have to look that up.” (My standard refrain to cover up my embarrassment because I can’t answer one of her questions about the natural world around me.)
But I had a theory: If mayflies arrive in here in June, perhaps they appear in May in other parts of the Midwest. I live at the western tip of Lake Superior. Everything in spring arrives late because around here winter doesn’t like to pack its bags and leave.
It turned out my theory had holes. In the United States, mayflies hatch anywhere from May to September. Hatching usually starts near the end of May but peaks in June or July, depending on latitude and the current year’s weather. The name mayfly may be a misnomer. But I like the name, so even if they don’t appear around here until June, I’m not starting a movement to rename them juneflies. (Besides there are beetles called June bugs.) Depending on geography, mayflies are also called shadflies, sandflies, dayflies, fishflies, and drakes.
I learned more about mayflies than their aliases. They’re fascinating and useful insects. This shouldn’t have surprised me because our ecosystem is like an intricately woven tapestry of nature. Pull on one thread and the effect ripples through the whole landscape. I was ignorant to assume their only purpose was to gross me out every June.
After mayflies become adults, they molt once. Every year I’d see their exoskeletons stuck to my screen doors, siding, plants, and deck furniture, and I’d cringe. Filmy, cracked, and devoid of color, exoskeletons are eerie. But after learning about mayflies, I look at their abandoned outwear and think about their amazing lives.
Mayflies are adults for only one or two days, and on rare occasions three days, accounts vary. They begin life in the water as fertilized eggs. After they hatch they’re called nymphs and spend about a year (depending on the species) lounging at the bottom of riverbeds and lake bottoms. While not as beautiful as the water nymphs of Greek mythology known for protecting gods and humans who were in peril, the mayfly nymphs are important. They help clean water by eating algae and detritus. And scientists use the number of mayfly larvae present in a river or lake as a bioindicator to gauge the water’s health. So mayfly nymphs can protect humans by informing us if our water quality is in jeopardy–if we’re smart enough to listen.
Before mayflies leave their water homes, they shed their nymph skins, so they can take flight for the first time. At this point they’re called duns (or subimagos). After coming to the water’s surface, they rest and dry their wings. Waterfowl and fish dine on some of them. The duns that survive the predators fly away from the water and molt one last time, becoming adults called spinners (or imagos).
After emerging from the watery homes of their adolescence, mayflies have only one concern–to mate and produce eggs. They don’t have functioning mouths so they can’t eat. As adults they don’t have to worry about finding food or feeding their young. They don’t have to worry about a career path or a mortgage. They don’t have to worry about saving for retirement or signing up for Medicare. As adults they molt, mate, lay eggs if they’re female, and die, all in a day or two.
Of course, a mayfly’s adult life isn’t completely worry free. If spinners are to achieve their one adult ambition–reproduction–they must avoid becoming fresh meat for fish and birds. They also need to conserve energy for mating and laying eggs. This explains why the mayflies I see on my screen door or deck are so impervious to me: It’s risky for them to use up energy by fleeing from me.
After molting, adult males return to an imaginary dance floor above the water. Flying up and forward, then floating down, they beckon the female spinners to dance with them. The spinners pair up and mate in midair. All this looks nothing like my first seventh-grade dance, where boys and girls stood on opposite sides of the gym and gawked at each other. [Watch BBC’s Beautiful Video Clip About Mayflies to see the mayfly mating ritual.]
After the circle-of-life dance, the females descend to the water to lay fertilized eggs. Some females become food for fish before they deposit their eggs. In my research, I learned fly fishers use tied flies resembling duns then spinners during mayfly season. But many females do deposit their eggs, which drift to the bottom of a river or lake. Then most females die, but a few manage to mate again and lay another batch of eggs because they have extra energy reserves, most likely because of what they ate as larvae. (But I like to imagine they have extra energy because they danced a slow waltz instead of a hot-footed jig during their first tango with a male spinner.) Two weeks later the eggs hatch into nymphs.
Before my mayfly education, when I saw mayflies clinging to my door or siding or deck furniture, I left them alone. I didn’t touch them because they creeped me out. Now I can say I leave them alone because I understand they’re saving energy for their big dance. Now, I can appreciate mayflies for purifying rivers and lakes, for working as bioindicators, and for being part of the food chain. Now, I can answer my granddaughter’s question about why mayflies seem to be misnamed.
We need to cherish mayflies and protect them, and if their numbers decrease in our lakes and rivers, we need to figure out why.
[To read more about mayflies: Mayflies: National Wildlife Federation and Britannica: Mayfly. If you live where mayflies swarm, read How to Survive a Massive Mayfly Swarm by Leslie Mertz, Ph.D. Don’t worry it’s not as scary as my imaginary horror flick, Return of the Giant Mayflies.]