Mayfly season in Michigan: Two days of sex, bright lights for pesky bugs

• Mayflies will begin to appear near Lake St. Clair, Lake Erie and other bodies of water in the coming weeks 
• They spend at most two days out of the water as adults solely to mate
• The insect doesn’t bite or sting and are completely harmless to humans

Michigan is home to over 100 species of mayflies, and hundreds of thousands of them are expected to swarm lakeside communities like St. Clair Shores in the next few weeks.

Despite attempts to track them by radar, the emergency of the summer nuisance is tough to predict, but they are likely to appear in southeast Michigan communities around Lake St. Clair by early June, said David Lowenstein, consumer horticulture extension educator at Michigan State University.

Also called “fish flies,” the giant mayfly— or Hexagenia limbata — can arrive as late as July in the Great Lakes basin.

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While the insects can be frustrating, they are a good indicator of air and water quality. 

“Mayflies are only found in aquatic habitats that are healthy,” Lowenstein said. “So a strong mayfly emergence … is actually a sign that the waterways are doing quite well.” 

Here’s what to know

Mayflies spend most of their life in water as larvae. They take a year or two to hatch, and they only live for about a day or so once they emerge to surface water as an adult.  

“One of the reasons that they don’t live for long above ground is because they don’t have mouth parts, so they can’t actually feed once they come out of water,” Lowenstein said. 

Lots of mating 

Once an adult mayfly emerges from the water, they spend the rest of their life mating. 

Mayflies in places like Georgia and other parts of the Southeast hold the record for shortest lifespan: 30 to 60 minutes. 

Once they’ve mated, the female lays a number of eggs on the water surface and the cycle continues. A female can lay up to 4,000 eggs. 

“When they’re not feeding, they’re hanging out near lights … in trees or other structures near the water in the daytime,” Lowenstein said. “It’s dusk and dawn when they are most active.” 

How do you know it’s mayfly season?

It’s tough to miss.

Around Lake St. Clair communities, for instance, millions of them congregate around gas stations, grocery stores, parking lots, ATMs or anywhere with lights. 

Because they die soon after mating, groups of dead mayflies can be found in piles stacked on top of each other. They stink like dead fish and crunch when they’re stepped on.

The good news: They don’t bite or sting. They are just annoying.

What can be done?

Not much. 

Lowenstein suggests that people who live by lakes and rivers keep porch lights off during mating season. Sometimes birds will feed off their carcasses, but eventually homeowners will need to get rid of what the birds leave behind. 

Nicole Polizzi of Miller Marina in St. Clair Shores told Bridge Michigan that they install red light bulbs around the dock to try to keep them away. It only helps a little.

“There’s nothing really to deter them,” Polizzi said. “They’re a harmless nuisance.”

The solutions: Sweeping the carcasses into Lake St. Clair, where the dead mayflies are eaten by birds and fish, Polizzi said.