Mayflies swarm Oneida Lake after disappearing for decades—why are they back?

Oneida Lake’s annual mayfly hatch once looked like scenes from a 1950s B-movie.

Each June billions of the bugs would emerge from the muck on the bottom of the lake, shed their skins, and fly inland in swarms big enough to show up on weather radar.

The blizzard of bugs plastered lakeshore homes and businesses, accumulating in drifts more than a foot deep in many places. Vast, undulating windrows of dead mayflies stretched across the lake’s surface.

Sometimes the mayfly maelstrom was so intense you wouldn’t know Oneida Lake existed. In 1957, Cornell University scientists had to postpone electrofishing operations on the lake because it was impossible to see the water through the dense mat of mayflies.

“When I was a kid back in the sixties they were so thick that South Bay Road would get covered with them and cars would literally slide off the road if they ran over them,” said Al Daher, co-proprietor of Mickey’s Live Bait & Tackle in North Syracuse.

But by 1969, mayflies mysteriously disappeared from Oneida Lake.

Then, for equally mysterious reasons, mayflies started coming back about ten years ago. Some recent hatches have been as epic as ones from the old days. Week after week, wave after wave, mayflies molting, mating, and dying.

How could such bountiful bug vanish virtually overnight? Why did they suddenly reappear some 50 years later? And what does it mean for Central New York’s most popular fishing destination?

‘Their numbers are just astronomical’

Mayflies live two to three years as tiny larvae munching on plant material at the bottom of shallow lakes and streams. They enjoy merely one glorious day of adulthood above the surface before they die.

In 1999, three decades after mayflies disappeared from Oneida Lake, the director of Cornell’s Biological Field Station at Shackelton Point found a single Hexagenia limbata, or giant burrowing mayfly hiding in a sample of lake sediment.

Now, more than two decades after this momentous discovery, the mayfly’s contribution to Oneida Lake’s food web is significant enough to warrant special attention in Cornell’s annual report on the health of the fishery.

At an April meeting of the Oneida Lake Association, Tony VanDeValk, director of Cornell’s field station, called mayflies the “dark horse” factor impacting fish populations.

“Their numbers are just astronomical in the early summer and the fish are definitely taking advantage of that,” he said, noting that the mayfly resurgence has been accompanied by an uptick in growth rates for yellow perch, a popular sportfish prized by anglers for its delicate flavor.

“Yellow perch are doing great,” VanDeValk said. “Not only are there a lot of them, but they’re big.”

In their first few weeks of life, ninety-nine percent of yellow perch are eaten by predators such as walleye, VanDeValk explained. The reason perch are doing great today is because Oneida Lake’s menu has expanded significantly.

Walleyes typically feast on perch fry in the spring. But now they’re filling up on mayflies, too, as well as round gobies, an invasive fish that spread to Oneida Lake around the time mayflies returned.

In other words, gobies and mayflies provide a tasty buffer—an appetizer for predators—allowing more perch to survive into adulthood.

“I think it’s a very good thing especially from a fishery standpoint,” said VanDeValk. “Mayflies improve fish growth, and they improve fish survival. I don’t see any negative effects to speak of.”

‘Eel-fly plague’

Mayflies might be great for Oneida Lake’s fish populations, but they’re not always so great for Oneida Lake anglers. From a fish’s point of view, no manmade bait or lure tastes better than a mayfly.

Local outdoors writers for years regularly blamed the “eel-fly plague”—that’s what they used to call Oneida Lake’s mayflies—for slow fishing seasons. One columnist for the Syracuse Herald-American lamented in 1948 that “the fish were too well fed on a delicacy they like.”

This once common complaint amongst anglers has been revived along with the mayfly’s fortunes. Tony Buffa, an Oneida Lake charter captain for almost 50 years, experienced his first big mayfly hatch only a few years ago.

“I’ve had the pleasure of having extremely good fishing all the way through the season without having the brakes put on from a massive mayfly hatch,” Buffa said. “So this has been a learning experience for those of us who’ve never lived through it before.”

Buffa says this year’s hatch was moderate compared to the previous two years when he couldn’t buy a bite at times.

“It was fierce,” Buffa said. “It was nuts. It turns the bite off. You have to be a magician to get decent catches. It’s not like there’s a portion of the lake that’s free from the mayflies. No, it’s lake-wide.”

Many anglers simply choose to go elsewhere or stow their rods—not an option for Buffa—rather than compete with Oneida Lake mayflies during a big hatch.

Matt Gutchess fishes the lake almost every day and posts instructional videos to his YouTube channel, The Awakening Angler. He’s not convinced that mayflies suppress Oneida’s walleye bite.

When he sees clusters of mayfly nymphs on his sonar swimming toward the surface, it’s a signal for Gutchess to get more aggressive with his presentation. He’ll snap his jig harder and faster to trigger a reaction bite from walleyes already filled to the gills with mayfly nymphs.

“But sometimes the fish are just off no matter what you do,” Gutchess noted. “Nowadays most guys have only a day or two to get out and go fishing. As long as it’s not lightning out, I’m not going to let bugs or anything else bug me, literally.”

A messy nusiance

Mayflies historically have been a messy nuisance for Oneida Lake property owners. The bugs pile up faster than lake effect snow, and they stink if left to rot.

When Eddie Stewart Sr. leased a hotdog stand that would later become Eddie’s Restaurant, a beloved Sylvan Beach landmark since 1934, he used a snow shovel to clear the sidewalks of mayflies, recalled author and Oneida Lake historian Jack Henke, who once interviewed Stewart for a book.

“Eddie told me how, during big hatches in the evenings, cars made noticeable popping sounds as their tires crushed the flies,” Henke said.

In the 1950s, John Hadyk’s family put up screens in all the windows and turned off all the house lights at night so as not to attract mayflies. Since it was Hadyk’s job to clean up the bugs, he developed a technique.

“I’d let them dry out,” Hadyk said. “If you swept them while they were still alive, they’d smear. Now you can just blow them away with a leaf blower, makes it a lot easier.”

Hadyk still lives on the lake and owns Johnnie’s Pier 31 restaurant and marina in Canastota. The mayflies can be annoying, he said, but he’s glad they’re back.

“It messes up the fishing, and of course it’s messy,” Hadyk said. “But we don’t have it as bad as Sylvan Beach, we’re pretty lucky.”

A mayfly reniassance

Why did Oneida Lake’s mayflies disappear in the first place? Nobody knows for sure. But in the 30 years that they went missing, Oneida Lake became much cleaner.

Mayflies are a good indicator of water quality. They thrive only in clean water with the right balance of nutrients and oxygen. The absence of mayflies in an otherwise suitable body of water is a red flag that things are out of whack below the surface.

VanDeValk said it’s possible that mayfly populations took a severe blow following prolonged periods of “hot, calm weather” beginning in the late 1950s which reduced oxygen levels at the bottom of Oneida Lake.

“They’re pretty intolerant of low oxygen,” said Thomas Evans, an aquatic biologist and research associate in Cornell’s College of Agriculture and Life Sciences. “That’s probably why they disappeared.”

But mayflies never completely disappeared. They eked out a shadow existence in Oneida Lake’s murky bottom for decades, their meager hatches going unnoticed by those who still remembered the maximum mayfly mayhem of the old days.

Conditions for mayflies began to improve with passage of the 1972 Clean Water Act, and later, with the 1992 arrival of zebra mussels. The invasive filter feeders gobbled up massive quantities of oxygen-depleting algae and cleared the water.

The stage was set decades ago for a mayfly renaissance. So why is it only happening now?

A mayfly experiment

Evans and Logan Lee, a bio-engineering student at Cornell, hope to shed light on that question with a new experiment housed in a large metal shed at Cornell’s field station. Inside the shed are 48 plastic containers filled with bubbling lake water, quagga mussels, and mayfly nymphs.

The arrival of quagga mussels in Oneida Lake about 10 years ago coincides with the mayfly resurgence, Evans said. Unlike their zebra mussel cousins, quagga mussels will colonize areas of soft sediment where mayflies spend most of their lives.

The experiment will show if quagga mussels are helping mayflies flourish by functioning as a kind of pump, Evans said, pulling nutrients down to the bottom of the lake.

“If that’s the case it may open up a chance for mayflies to eat what they really can’t get access to in the water column,” Evans said. “Now that you’re pumping all this nutrient down, they’re doing really, really well and they take off.”

Two months ago, Lee, a Long Island native, had never even seen a mayfly.

“The first time I saw the shed,” said Lee, referring to the massive quantity of skins mayflies leave behind before getting their wings, “I didn’t know they were mayflies. I tried to get in a kayak and the thing was covered in mayflies.”

“It was kinda gross,” he added, “but it was cool to see there were so many.”

The experiment will wrap up by the end of summer. We may never get clear answers about what killed off Oneida Lake’s mayflies, or why they came back. But the people and critters that call the lake home have already adjusted to the bug’s relatively sudden, briefly overwhelming, and occasionally gross presence.

Al Daher, an avid trout angler, hopes Oneida Lake’s mayfly renaissance will spread to creeks and streams around the region. Over the years he’s noticed a worrying decline in mayflies and caddisflies that trout love to eat.

“We depend on hatches,” he said. “It’s quite the phenomenon we’re seeing them now. It’s a good sign.”

Steve Featherstone covers the outdoors for The Post Standard, syracuse.com and NYUP.com. Contact him at sfeatherstone@syracuse.com or on Twitter @featheroutdoors. You can also follow along with all of our outdoors content at newyorkupstate.com/outdoors/ or follow us on Facebook at facebook.com/upstatenyoutdoors.