Mayflies, which form swarms in the billions that are visible on weather radar, are in steep decline, mirroring the plight of insects worldwide. 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, according to a study published today in Proceedings of the National Academy of Sciences. Levels of neonicotinoid pesticides have risen in recent years in Lake Erie and many freshwater systems in the Midwest. The chemicals, which are toxic to many insects, have been measured in Great Lakes tributaries at levels 40 times greater than protective levels set by the U.S. Environmental Protection Agency’s Aquatic Life Benchmark, according to a 2018 study.
Source: National Geographic, Jan 20, 2020
https://www.nationalgeographic.com/animals/2020/01/mayfly-insect-popula…
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