Mayfly Numbers Down 50% In Midwest Since 2012; W. Lake Erie Species Down 84% 2015-19

Every summer, mayflies burst forth from lakes and rivers, taking to the skies of North America. These insects, which are particularly abundant in the northern Mississippi River Basin and Great Lakes, live in the water as nymphs before transforming into flying adults. they synchronize their emergence to form huge swarms of up to 80 billion individuals—so massive that, in waterside towns, they are sometimes scooped up with snowplows.

These insect explosions provide food for a wide variety of animals, from perch and other commercially important freshwater fish to birds and bats. But new research shows that mayflies are in decline. Since 2012, mayfly populations have declined by more than 50 percent throughout the northern Mississippi and Lake Erie, likely due to pollution and algal blooms, according to a study published today in Proceedings of the National Academy of Sciences. “We were really surprised to see that there was a decline year after year,” says lead author Phillip Stepanian, a bio-meteorologist at the University of Notre Dame. “That was really unexpected.”

These swarms are so big and thick that they appear on weather radar used to track rain and snow, and for a long time, meteorologists ignored these signals as a type of “noise,” he says. But Stepanian, who was trained as a meteorologist, realized these signals could provide useful information about populations and movements of animals like birds and insects, including mayflies.

in the paper, Stepanian and colleagues used radar to estimate mayfly populations, validating the method by comparing it with numbers of mayfly nymphs found in the sediment at the bottoms of rivers and lakes. The study revealed that between 2015 to 2019, populations of burrowing mayflies in the genus Hexagenia declined by an incredible 84 percent in western Lake Erie. In the nearby northern Mississippi River Basin, from 2012 to 2019, they declined by 52 percent. These dropping populations are significant because the insects are an important link in the food chain, serving as prey for a variety of predators. They also transfer tons of nutrients from the water to the land, a valuable ecological service.

EDIT

https://www.nationalgeographic.com/animals/2020/01/mayfly-insect-populations-in-decline/#close