More about Mayflies in Pittsburgh


Photo of adult mayfly Mayflies hatch from eggs that are deposited into the bottom sediment of fresh water bodies, then spend 1 to 3 years as nymphs underwater, burrowing in sediment and eating algae and other organic matter. When enough time has passed and conditions are right (primarily temperature conditions), these nymphs transform into sub-imagoes and ascend to the water surface. The sub-imago, also known as a dun, is not yet adult but is fully winged. The dun rests on the surface of the water until its wings are dry, then sets flight.
© Edward Ross

The adult lives less than 24 hours, and its sole purpose is to find partners and mate before it dies. The adults of many mayfly species don't even have mouths and digestive systems, because they don't live long enough to need them.

Mayflies fly in swarms, and mate in flight. The male dips up and down in the air, while the females fly straight through the swarms until caught by a male. After mating, the female lays up to 8000 eggs in the water, which then sink to the bottom and soon hatch into a nymph. After mating and laying eggs, mayfly adults die and fall back into the water, becoming food for fish, frogs, and other aquatic life.

View of Pittsburgh from Mount Washington

Since the dawn of the Industrial Revolution, Pittsburgh has gained a reputation as a dirty, polluted steel town--a reputation that, until the 1970's, was largely true. The city has made major efforts to clean up its environment, including the three major rivers that converge downtown. The return of the mayflies to urban Pittsburgh is indication that tremendous progress has been made.

A similar re-emergence of mayflies occurred on Lake Erie in 1999. Lake Erie had not seen large numbers of mayflies since the 1950's, when industry began to discharge massive amounts of organic pollutants into the lake. Mayflies are an important indicator not only of water quality, but also of the quality of bottom sediments, where organic and other pollutants often settle and remain for years.

For more information about mayflies, visit any of the links below.


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