Mayfly Life Cycle

Mayfly Nymph Courtesy Robert Henricks, Photographer Found on Licensed through CC BY-SA
Mayfly Nymph
Courtesy Robert Henricks, Photographer
Found on
Licensed through CC BY-SA
It’s commonly believed that mayflies live for only one day. If you visit a cold, clear river in the spring or early summer, you might see what is known as a “mayfly hatch,” when millions of delicate, glassy insects suddenly appear on the surface of the water, take to the air, and then fall into the river later that day and apparently drown.

The truth is mayflies live for much longer than one day, but like many other aquatic insects, their life cycle consists of a long period during which almost nothing happens, followed by a sudden and dramatic burst of activity.

The mayfly begins life as an egg so tiny it’s nearly invisible to the naked eye. The egg sinks to the bottom of the river, and a couple weeks later a mayfly nymph hatches. Speckled and primitive-looking, the nymph simultaneously resembles a crab, shrimp, and troglodyte. For one entire year (and in the case of some species, two years), they grub around the streambed eating algae and hiding from trout. Lift a rock from a mountain stream and turn it over–if the stream is unimpaired by pollution or water quality problems, you’ll likely see a mayfly nymph doing what it does best: waiting in the mud for its birthday.

Mayfly Imago Courtesy J Schoen, Photographer Found on Licensed through CC BY-SA
Mayfly Imago
Courtesy J Schoen, Photographer
Found on
Licensed through CC BY-SA
In the spring, when its big day arrives, the nymph leaves the blackness of the streambed and heads for air and sunlight. But the nymph is so small and weak, the water’s surface is like a rubbery membrane that it must pierce and wriggle through. Then the nymph sheds its skin and emerges as a dull-colored and clumsy flying insect called a “sub-imago,” or what fly anglers call a “dun.” Practically weightless, they stand on the water, drifting downstream likes fleets of tiny sailboats as they wait for the UV light of the sun to harden their wings so they can fly away.

Mayfly Imago Courtesy Audrey Zharkikh,, Photographer Found on Licensed through CC BY-SA
Mayfly Imago
Courtesy Audrey Zharkikh,, Photographer
Found on
Licensed through CC BY-SA
It’s difficult to overstate how fragile and helpless a mayfly dun is. As the mayflies float up through the current, fight their way out of the water, and then surf along the waves, fish gorge themselves on them. When the mayflies get airborne, there are swallows and other birds to worry about. Even strong breezes and rough water can be catastrophic to duns. Luck is the only thing they can rely on.

But if the mayfly can escape the river and hole up in the bankside vegetation for just a couple hours, its skin will split open again, and a bolder, stronger creature will emerge. Now called the “imago” (fly anglers call them “spinners”), this stage can fly faster and more skillfully than before, and they use this agility to accomplish their final acts–find a partner, mate in mid-air over the stream, and deposit the seeds of a new generation in the water. Then, exhausted, the spinners die and fall back into the river, where the fish feed on them once again.

And so it’s easy to understand why some people mistakenly believe that mayflies live for only one day–by the time we see them emerging, they have only one day left to live. It’s almost as if, after a lifetime of staying home, the mayfly suddenly decides it’s time to get out and see the world, find love, and have a family, but they have to do it all that same day. Is there a lesson for us in the life cycle of a mayfly? Something about not waiting too long to do the things you want, or living every day as if it’s your last? The answer to this question, and possibly others, can be found by visiting cool, clear mountain streams in the springtime or early summer.

For Wild About Utah this is Chadd VanZanten.

Photo credit #1: henricksrobert via / CC BY-SA
Photo credit #2: jschoen2000 via / CC BY-SA
hoto credit #3: andrey_zharkikh via / CC BY-SA
Text: Chadd VanZanten

Additional Reading:

Craig Macadam, The mayfly’s lifecycle: a fascinating, fleeting story, The Freshwater Blog, May 16, 2011,

Biology 5445, Entomology (Feener),

Distribution of mayfly species in North America, List compiled from Randolph, Robert Patrick. 2002. Atlas and biogeographic review of the North American mayflies (Ephemeroptera). PhD Dissertation, Department of Entomology, Purdue University. 514 pages and information presented at Xerces Mayfly Festival, Moscow, Idaho June, 9-12 2005,

A “no-trouts-land” on the Logan River

Cutthroat Trout A no-trouts-land on the Logan River, Copyright (c) Chadd VanZanten, Photographer vanzanten-cutthroat_trout.250x184
Cutthroat Trout
Copyright © Chadd VanZanten, Photographer
Northern Utah’s Logan River is known for its solitude and grandeur. Drive just a few miles up Logan Canyon in Cache Valley and find yourself in a wild setting on the bank of a picturesque mountain stream. It would be difficult to find a place in Utah that is more accessible and yet so peaceful.

However, just a few inches beneath the riffles of the Logan River, a war rages.

This conflict has gone unresolved for more than a century. The combatants fight continuously all day, all night, and all year.

The indigenous defender is the Bonneville cutthroat trout, which migrated here hundreds of thousands of years ago from the west coast of America by way of the Snake and Columbia rivers. They’ve been here ever since, making this Logan River cutthroat army the largest wild and natural population of its kind. Presently, cutthroats hold the upper river, above Twin Bridges or thereabouts.

Invading from downstream is the brown trout, whose antecedents hail from Eurasia. The brown trout isn’t an intentional trespasser; they were stocked here in the 1880s by humans who wanted more fish to catch. However, brown trout are aggressive, and they don’t know or care that the Logan River used to belong to some other species. Brown trout dominate the lower river, especially in the neighborhood of Third Dam.

And so they fight.

The middle portion of the river is a “no-trouts-land,” where the two species meet to wage their desperate struggle. They contend for living space, compete for forage, and, when it’s convenient, they devour each other with gusto.

Which will prevail? Each species has its advantages.

The brown trout are indisputably stronger, tougher, and meaner. They tolerate low water quality and wide swings in water temperature. When brown trout encounter cutthroats of their same size, they aggressively drive out the more-docile cutthroats. Every year, the brown trout gain a little ground, pressing inch by inch upstream.

Cutthroats may not be great fighters, but they are resilient, having survived clear-cut logging, overgrazing, and the damming of the river. The cutthroats were here first, too, so they hold the high ground, and it’s much easier for fish to move downstream than up. And the cutthroats rule the upper tributaries of the Logan River, which they use to spawn and replenish their numbers. But perhaps most importantly, the cutthroats have an immensely powerful ally: humans.

That’s right. The race that brought the brown trout here in the first place now sides with the cutthroats. The humans could easily exterminate all brown trout in Logan River, from its headwaters to the confluence of the Bear River, but that’s not what’s happening. Instead, conservation measures, such as strategically placed barriers to fish passage and fishing regulations that protect cutthroats during their spawning season, give the natives a fighting chance against their fierce invaders.

Fly anglers, too, favor the cutthroat trout, which they fondly refer to as “cutties.” Fly anglers seem averse to harvesting cutties, releasing them instead unharmed after capture. Opinions vary among experts about how much catch-and-release practices actually help the Cutthroats, but this is war, and these natives, besieged by a relentless and superior foe, can use every advantage they can get.

For Wild About Utah I’m Chadd VanZanten.

Images: Courtesy and Copyright Chadd VanZanten, Photographer
Text:     Chadd VanZanten

Additional Reading:

The Cutthroat Trout, Anna Bengston, Wild About Utah, July 10, 2014,

Cutthroat Trout, Native trout of the interior west, Utah Division of Wildlife Resources,

Small Stream Cutthroat Trout, Matt McKell, May 10, 2016,