Mayflies fly as may flies by

Mayflies may seem like a one-day wonder, but theyre also a sure indicator of good water quality.

May marks the month when the mayfly species begin to emerge from the water. The insects begin life in the water and live as naiads (immature stage) for several months or several years, depending on the species, until they emerge from the water as winged adults. Adults live only but a day — just long enough to mate and lay eggs.

Mayfly is really a misnomer because various species emerge every month from May through September. They are also not flies, but belong to the order Ephemeroptera, from the Greek word ephemeros — short-lived, and pteron — wing, referring to the short life span of the winged adults. Flies belong to the order Diptera, meaning two wings. Anyone who fishes knows mayflies as excellent bait for fly-fishing. Others with lakeshore property may know them as a summer annoyance, as the insects can be quite abundant when they emerge.

But mayflies are harmless to humans and are a great indicator of water quality. There was cause for rejoicing in 1987 when mayflies returned to the Mississippi River in the Twin Cities after a 30-year absence. Their presence meant that the efforts to reduce pollutants (namely raw sewage) to the river had resulted in a definite improvement in the water quality.

More about mayflies

• Life cycle of mayflies at the US EPA web site
• Mayfly emergence chart at Minnesota Fly Fishing
• Mayflies as water quality indicators at the Minnesota Pollution Control Agency web site