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Is the abundance of mayflies an indicator of high or low quality water in the Lake?

Mayflies are generally indicators of good habitat and water quality. The common mayfly in Lake Erie is called the "Burrowing Mayfly." It has a very interesting life cycle. After it hatches from an egg, the larvae spend 2 years living in the bottom of Lake Erie. It is approximately 1 inch long and has feather-like gills protruding from the sides of its abdomen. It digs a U-shaped burrow in the bottom of the lake with two openings. It then sits in the burrow and pumps water through it using its gills. It eats the organic material in the water that flows through the burrow. It is not tolerant of low oxygen levels. After 2 years it swims to the surface, sheds its exoskeleton, emerges as an adult, and flies toward lights on shore. It lives for 48 hours as an adult and has no mouth parts. It cannot bite or feed. Its sole purpose is to mate and lay its fertilized eggs over the water, where they sink to the bottom and the cycle starts again. Because they are not tolerant of low oxygen levels or contaminated sediments, they are generally considered to be indicators of good water quality.

Jeffrey Reutter, Ohio Sea Grant College Program