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Spokane, Washington  Est. May 19, 1883
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Bugging the Northwest: The fascinating, fleeting and sometimes gross life of the mayfly

This adult mayfly was photographed by Angela Winner at Soos Creek southeast of Renton in early April. The presence of mayflies indicates the water is cool and clean.  (Courtesy: Angela Winner)
This adult mayfly was photographed by Angela Winner at Soos Creek southeast of Renton in early April. The presence of mayflies indicates the water is cool and clean. (Courtesy: Angela Winner)
By Linda Weiford The Spokesman-Review

With bugs, we’re never alone – especially this time of the year.

Visit a lake, pond or stream at dusk and you’ll likely see a display of the mayflies’ delicate wings frantically fluttering above the water.

Sporting glittery wings, long, slender abdomens and two or three wispy tails, large numbers of these insects can feel like an invasion. But seeing them is a good thing. They don’t bite or sting. And most importantly, because mayflies are sensitive to pollutants, large populations mean the water is clean.

Because most adult mayflies only live up to 24 hours, the bug in this column’s photograph from April 1 is long deceased.

Amazingly, if the insect managed to survive a full 24 hours, it led a long life. On the Savannah River in Georgia, the adult species Dolania americana lives just five minutes.

With such short lifespans, “mayflies are one of those insects that probably best survive by producing in great numbers,” said entomologist Richard Zack of Washington State University. During the insect’s remarkably short adult life, it must find a mate, copulate, and lay hundreds of eggs in the water from which it came, he explained.

Depending on the species and water conditions, the nymphs take anywhere from a few days to a few months to hatch. Residing in the bottom of the lake or riverbed, they quietly forage on algae and decomposing vegetation, shedding their skins before emerging as elegant flying adults.

“Only so many survive but the few that do, carry on the species,” Zack said. And it’s a good thing they do, since mayflies are a major food source for fish, birds, bats and other insects, he added.

Which is why anglers appreciate mayflies as much as entomologists do. Trout, salmon and bass devour them, so fishermen often tie imitation flies to fool the fish into biting.

There are roughly 500 different mayfly species in North America – 109 here in Washington state, according to “Mayflies of the Far Western United States,” published in Transactions of the American Entomological Society, 2007. Some of our resident adult species are just a few millimeters in length; others measure more than an inch-and-a-half long. While some typically emerge in spring, many more appear in summer, including the Light Cahill. Commonly found in Inland Northwest waterways is the Red Speckled Dun.

Epic mayfly emergences are more common east of the Rockies than in the Pacific Northwest. Sometimes their swarms get so massive and dense over Lake Erie and the Mississippi River that they show up on radar like storm systems.

“When mayflies emerge from the water, they do so at the same time, and with some species, there can literally be thousands and thousands of them coming out,” Zack said.

Unfortunately, the short-lived, flying adults so eager to mate and lay eggs get attracted to outdoor lights when it’s dark. Consequently, crunchy carcasses can coat bridges, boats and roads a day after a large emergence.

If you hate bugs, this might be one of the grossest columns you’ve read. Even so, Zack encourages a favorable perspective. After all, their presence means the water is clean, the weather is good and neighboring fish, birds and bats have lots of nutritious food to eat.

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