Fly Fisherman Throwback: Pale Morning Duns: The Most Important Mayfly Hatch in the West

Editor's note: Flyfisherman.com will periodically be posting articles written and published before the Internet, from the Fly Fisherman magazine print archives. The wit and wisdom from legendary fly-fishing writers like Ernest Schwiebert, Gary LaFontaine, Lefty Kreh, Robert Traver, Dave Whitlock, Al Caucci & Bob Nastasi, Vince Marinaro, Doug Swisher & Carl Richards, Nick Lyons, and many more deserve a second life. These articles are reprinted here exactly as published in their day and may contain information, philosophies, or language that reveals a different time and age. This should be used for historical purposes only.

This article originally appeared in the June 1989 issue of Fly Fisherman magazine. Click here for a PDF of the print version of "Pale Morning Duns."

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The Pale Morning Dun is probably the most important mayfly hatch in western North America. You'll find them from the soft currents of Fall River in California to the bouncing riffles and runs of the Madison in Montana, from the wide expanses of the Henry's Fork in Idaho to the secret side channels of the Bow River in Canada, and from the gentle glides of the Frying Pan in Colorado to the great runs of the Green in Utah. Find a good trout stream in the West, and the odds are good that it sports a good hatch of Pale Morning Duns.

Their vast distribution is not the only factor that makes these olive-yellow mayflies so important. The peak of the Pale Morning Dun hatch occurs in midsummer, while most trout water in other parts of the continent sleeps through the dog days, waiting for the cool autumn nights to give new life to its treasures.

Pale Morning Duns belong to a large family of mayflies known as Ephemerella and three species: infrequens, inermis, and lacustris were initially identified as important to the trout fisher. Later studies indicated all three of these species may not be equally important. Identification of exact species is so difficult that some confusion about them still exists among the scientific fraternity. My own research indicates that inermis far outdistances the other species in angling importance. The most important point to realize is that all three species are virtually indistinguishable to the eyes of the trout fisher and, more importantly, to the trout.

My first experience with these insects goes back to before I even knew what a mayfly was. I spent many bright summer days fishing the soft, weed-lined flats of the upper Teton River near my home in Idaho and watched the big cutthroats feed softly on the tiny yellow mayflies. I hated them, because once they appeared on the surface, the big fish quickly lost interest in my wet-fly offerings. On rare occasions, using a Light Cahill I was rewarded with a token fish after the dreaded yellow flies appeared. I didn't know what they were, but I knew the trout loved them.

I discovered what the yellow insects were when I received a copy of the now classic book Selective Trout, by Doug Swisher and Carl Richards. I was amazed to read about water in my back yard, the Henry's Fork of the Snake. I read all I could about the little mayflies I had grown to know so well, the Pale Morning Duns.

Since those apprentice days I have fished magnificent hatches of Pale Morning Duns, also known here as PMDs, on the great trout streams of the West. A good morning hatch of them once saved an otherwise loser of a day for me on the Beaverhead near Dillon, Montana. Memorial Day often found me on the Firehole River in Yellowstone Park, looking for those first hatches of the yellow mayflies. I still eagerly anticipate each Opening Day of fishing on the Henry's Fork to meet the first hatches of the Pale Morning Duns.

Where To Find Them

Although most western trout streams support good populations of Pale Morning Duns, the greatest concentrations occur in streams with medium-velocity currents. The nymphs are sprawlers and thrive on rocky or gravel bottoms interspersed with good stands of aquatic vegetation. On some streams their population densities are astounding, with hundreds of nymphs per square foot of stream bottom. The nymphs are robust and vary greatly in color from a pale yellow-olive to a deep olive-brown.

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Pale Morning Duns range in size from 6mm to 9mm long, corresponding with #14 to #18 hooks. Like several other mayfly species, the flies get smaller as the season progresses. This phenomenon was first pointed out to me by Fred Arbona during his research on his book Mayflies, the Angler, and the Trout. Early in the season the Pale Morning Duns are best matched with size 14 and 16 hooks. Later, in August, the same species will be at least a full size smaller and are matched with size 16 or 18 hooks. This factor may account for the early confusion in species identification by angling entomologists. The differences in body coloration of the duns can also lead to confusion. The females run a pale yellow-olive to pale chartreuse, while the males often have a pronounced rusty color. The wings are light to medium gray and often show a distinct yellow on the leading edge, especially on the females.

Emergence is greatly influenced by a variety of conditions including water temperature, humidity, and light intensity. On spring-fed streams, the hatches may continue over a period of several months because of the constant water temperature. On freestone streams, where the water temperature varies throughout the season, the hatch may last only two weeks.

Because Pale Morning Dun hatches occur over a period of several weeks on most trout streams, the emergence of duns and spinner falls often vary in intensity and time of day, according to the influencing conditions. Since the hatches continue through the warmer months of the season, the best activity usually occurs on cool, humid, overcast days. Unlike many mayfly species, each stage of the life cycle of Ephemerella inermis is of considerable value to the fly fisher. To be successful, you should become familiar with each stage and learn to capitalize on each fishing opportunity.

Fishing the Hatch

I've had my best nymph fishing during and just prior to the hatch. The nymphs generate energy just before they emerge, and wiggle and twist as they ascend to the surface. The trout waste no time in taking advantage of this opportunity. In spite of the activity, nymph fishing during these conditions can be frustrating and unsuccessful. Since the nymphs are buoyed to the surface as their body processes change, they drift down the feeding lanes, where the trout hold to intercept them. Any unnatural drift will be ignored by all but the smaller fish. Fishing a small nymph with a drag-free drift can be much more difficult than fishing a dry fly on the surface. For that reason, blind casting the nymph randomly among the feeding fish usually brings little success.

Whenever possible, I like to cast my nymph imitation to a visible, sighted trout. This is impossible under many conditions, but on clear, spring-creek waters it can be an effective method. After you spot the fish, determine the drift lane from which he's picking his food. Cast the nymph a few feet above the fish and allow it to drift naturally through his feeding lane. You might need to grease most of your leader to keep the fly from sinking all the way to the bottom. Usually you won't feel anything or even see a slight twitch in the line or leader. You must have a "feel" for where your pattern is and look for the telltale white mouth as the fish opens to intercept your offering. Often the fish will just turn his head slightly as he takes the fly. This take can be one of the most exciting fly-fishing experiences.

Since many situations won't allow you to actually see the fish, an alternative method is to use a strike indicator. There are many types of indicators available, and all work, if they're fished correctly. Some of my own favorites are small, one-inch plastic sleeves, the pinch-on foam indicators, or a small piece of bright yarn tied with a clinch knot to the leader. I like to position the indicator according to the depth of the water I'm fishing, usually two to four feet above the fly. Although indicators are designed to help you determine the soft take, I find them even more valuable for maintaining a natural drift of the fly. Watching the indicator gives you a better idea of how the nymph is performing under the surface, and it allows you to mend and manipulate the line to correct the drift.

Several years ago I was fishing a favorite stretch of the Madison River. The Pale Morning Duns were starting to hatch when I arrived, but I saw few fish rising. I decided to try a nymph and knotted a #16 Pheasant-tail Nymph to my 5X tippet. I found a nice pocket where the current flowed between two large rocks and fed into a long slick below. I knew there had to be good fish working there on the emerging nymphs in the margin between the fast water and the slick.

I expected a strike on every cast, but my enthusiasm soon waned after dozens of fruitless casts. I sat on the bank and considered changing flies. I noticed some bright orange yarn in my vest, so I clipped a small section off and tied it to my leader with a clinch knot about three feet above the fly. I waded back out and took up my same position. The first cast saw the indicator go slicing through the current with unnatural drag. I knew that as the indicator went so went the nymph. My position made it impossible to accomplish a drag-free drift with the nymph. I found a better angle, and this time I watched the indicator drift down the slot in a natural, drag-free drift.

On the next cast the indicator hesitated; I tightened the line and was fast into a racing, high-jumping rainbow. I took several nice trout from the run and was equally successful at each of the next spots I fished. The indicator helped me detect the subtle takes, and it indicated the telltale imperfections of the drift that would surely lead to refusals.

I believe that presentation is much more critical than pattern when fishing the nymphs of the Pale Morning Dun. Usually a size 16 or 18 Pheasant-tail Nymph does the job. On occasion a pale olive nymph tied with natural fur and ostrich herl works well on selective trout, especially on clear Montana spring creeks.

Duns and Emergers

I've experienced my most frustrating moments fishing to the selective rainbows of the Henry's Fork during a midsummer hatch of Pale Morning Duns. The hatches are influenced by such a variety of climatic conditions that the angler must be prepared with a range of dry­fly patterns. The variety of the water fished also has a great influence on the most effective imitations.

Early in the season the duns usually start emerging at about 10 or 11 A.M. As the season progresses and the days get warmer, the duns begin earlier and last only a short time, and then begin again in late afternoon. On cloudy days the hatch can quickly become full­blown, and flies carpet the water. During prolonged dry weather, the duns hatch sporadically throughout the day. The type of water you fish dictates the requirements for the most effective imitation of the dun. Since good hatches of Pale Morning Duns occur on all types of water–including fast, medium, and slow currents–you should be prepared with fly patterns that are best suited to the stream configuration. As an example, it's hard to beat a delicate no-hackle for the softly flowing, weed-lined glides of a spring creek. But the same no-hackle would quickly be dashed under the surface of a brawling, fast-flowing river like the Gallatin. For fast-flowing streams where visibility and floatability are paramount, I like a fully hackled, standard pattern to imitate the dun. Another important pattern to help fill in the gap is a thorax or parachute.

Unfortunately, the correct fly pattern tied to represent the fully hatched dun at the peak of emergence is no guarantee of success. Pale Morning Duns drift a considerable distance after they break free of the nymphal shuck, and before they raise their wings to the upright position. I've observed the duns sitting in the surface of my aquarium for several minutes before they get their wings up to become airborne. During cool weather, the trout feed selectively on these emergers with wings folded in the clown position.

You must be prepared with a variety of emerger patterns to be successful in this downwing emerger situation. One of the best emerger patterns is the floating nymph. The clump of clubbing that forms the wing case represents the folded wing and provides visibility. The fly should be dressed, and it should be fished flush in the surface film.

Another effective pattern is the soft­hackle emerger, which incorporates a soft hackle, wound wet-fly style at the front of the fly. Although this fly works great on flat water, it's equally effective on broken water. It can be dressed and fished in the surface film like a floating nymph or fished wet, just under the surface.

My third emerger choice is the Quillwing Emerger designed by Rene Harrop. This pattern is tied with short, duck-quill wings and is a killing pattern when the selective trout are tuned into the slow-developing duns. I've never seen more selective trout than those that feed on the hapless duns that did not survive the ordeal of emergence.

The trout ignore some of the duns that drift over them and continue to rise to the cripples and drowned duns that seem to appear invisible to the angler. The riseforms are usually subtle, slow, and deliberate.

Several patterns to represent the dead and dying duns have proven effective for me. Harrop's Captive Dun represents the dun that didn't get its wings unfolded. The pattern trails a marabou tail to represent the still­attached nymphal shuck. This fly should be fished flush in the surface film. Another good pattern is the Drowned Dun, which is tied with duck-quill wings, like the No-hackle, but the wings are tied in the spent position. It also has a trailing nymphal shuck represented by sparse strands of yarn. I often cut one of the wings off on the stream, because many drowned duns drift downcurrent tipped over on one side.

Even with the correct pattern, the fishing can be difficult. Since the productive patterns are designed to drift flush in the film, they are impossible to see. In addition, you must carefully time the casts to coincide with the gentle rises of the trout, which usually have all day to leisurely feed.

PMD Spinners

The spinner fall of the Pale Morning Dun is as important to the Western fly fisher as the hatch itself. Mating flights usually occur both mornings and evenings. In June and early July I've had my most productive fishing to the spinner falls during the late evenings. I've often failed to notice the change from the greedy rises of a caddis emergence to the soft, gentle riseforms of the spinner fall during the last moments of daylight. Later in the season, especially during August when the days shorten and the evenings are cool, I find the best spinner falls occur during morning hours.

The spinners usually mate, lay their eggs, and die the day after they hatch. Sometimes they hit the water in unbelievable numbers, with several hundred crumpled bodies per square foot of surface area. I make a special effort to be on the water, armed with spinner imitations, the first bright, clear morning after days of cool, cloudy weather. As I've previously mentioned, the duns hatch in good concentrations on cloudy days, and the potential for a great spinner fall is excellent on a bright, warm day, preceded by a cloudy day.

The spinners like to drop their eggs where the current speeds up. You'll find some of the best fishing in and just downstream of a riffle area. The bigger trout take up the prime feeding locations in the margins of the riffles, in the pockets and slicks, and in front of large rocks.

With good numbers of insects, the largest fish quickly develop an intense feeding rhythm, rising several times in succession and then holding for a few moments before rising again. In addition, they often cruise back and forth across the feeding lanes, gulping the spinners by the mouthful. Coupled with low-light conditions, this situa­tion can be one of the most challenging in all of fly fishing.

I've stood in the Henry's Fork many evenings and watched as anglers all around could not catch the fish feeding on spinners. Precision casting is essential, and timing the rise is of the utmost importance. You can wade quite close to trout greedily stuffing themselves on Pale Morning Dun Spinners. Take advantage of this and work close enough to a feeding fish to get as many drifts as possible without false-casting.

It may take dozens of casts before a trout selects your pattern among the hundreds of naturals, and you don't want to waste casts by false-casting. Short casts greatly increase your accuracy and give you a better idea of where your fly is. Since spinners are virtually impossible to see, tighten the line each time you see a rise near where your fly should be. Usually you come up empty, but even a blind hog occasionally finds an acorn. It's hard to describe the excitement you'll feel when you tighten and the resistance is there.

Pale Morning Dun spinners come in two colors, and you'll find both varieties on the water at the same time. The females retain essentially the same pale yellow coloration they have as duns, while the males turn a rusty brown. Since virtually all the females end up on the water sooner or later to lay their eggs, you'll need patterns with pale yellow bodies. You'll also need rusty spinners to match the males. While I'm not saying that the trout always show a preference for color, it's wise to have patterns in both colors. I've usually found a pale yellow spinner to be more productive on bright, clear mornings. In the low light of dusk, a rusty spinner often outproduces a yellow one, because the dark body offers a better silhouette against a gray sky.

My favorite pattern is the simple Hen Spinner. I tie the wings in the spent position so the fly drifts flush in the surface film. Since the wings of the natural are clear, I like to use medium gray hen­hackle tips to blend with the sky. I believe wings that are too light in color show too much contrast to a trout viewing the fly against a bright blue sky. Sometimes I wind a dun hackle through the wings and clip it on bottom to add a little visibility.

While larger insects like the salmon flies or the Green Drakes have become legends to Western anglers, the hatches are often unpredictable. Even when larger insects like the Green Drakes are hatching in good numbers, trout often feed selectively on the smaller Pale Morning Duns.

Roy Palm, owner of the Frying Pan Angler in Basalt, Colorado, related an example on the Frying Pan River. Two large trout fed each day on Pale Morning Duns, a hatch that coincided with the Green Drake hatch. Whenever a large Green Drake dun drifted over either of the trout, they went down and stopped rising for a time. They reacted as though they were afraid of the larger mayflies.

Roy finally caught one of the fish on a Pale Morning Dun Emerger, and it had a Green Drake imitation stuck in its lip. The trout had reason to be more confident feeding on the smaller mayflies. The Pale Morning Duns are the real heroes of the West, even if they don't get the recognition they deserve.

Pale Morning Dun Fly Recipes

Pale Morning Dun Nymph

• HOOK: #16, Tiemco 3761 or Mustad 3906B.
• THREAD: Pale olive prewaxed 6/0.
• TAILS: Lemon woodduck flank.
• ABDOMEN: Hare's ear dyed light olive-brown, ribbed with fine gold wire.
• THORAX: Light olive-brown ostrich herl.
• WING CASE: Dark gray mallard quill segment.

Pale Morning Dun No-hackle

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0. TAILS: Light dun hackle fibers.
• BODY: Pale yellow-olive dubbing.
• WINGS: Medium gray mallard quill segments.

Pale Morning Dun Floating Nymph

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• TAILS: Light dun hackle fibers, flared to form a fan.
• BODY: Pale yellow-olive dubbing, ribbed with light olive monocord.
• WING CASE: Medium gray dubbing forming a clump over the thorax.

Harrop Captive Dun

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• BODY: Pale yellow-olive dubbing.
• TAIL: (Trailing shuck) Pale yellow-olive marabou.
• LEGS: Light gray partridge hackle fibers.
• WING CASE: Mallard quill segment pulled forward over the body.

Pale Morning Dun Soft-hackle Emerger

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• TAILS: Lemon woodduck flank feathers.
• BODY: Pale yellow-olive hare's ear dubbing, ribbed with light olive monocord.
• HACKLE: Medium gray hen hackle, wrapped wet-fly style.

Pale Morning Dun Spinner (Female)

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• BODY: Pale yellow-olive dubbing.
• TAILS: Medium dun hackle fibers, splayed.
• WINGS: Medium dun hackle tips, tied spent.

Pale Morning Dun Spinner (Male)

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Brown prewaxed 6/0.
• BODY: Rusty brown dubbing.
• TAILS: Medium dun hackle fibers, splayed.
• HACKLE: Medium dun hackle tips, tied spent.

Harrop Quill-wing Emerger

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0. BODY: Pale yellow-olive dubbing, ribbed with fine gold wire.
• WING: Mallard quill segments tied short, on the sides of the thorax.
• LEGS AND TAILS: Lemon woodduck flank fibers.

Drowned Pale Morning Dun

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• BODY: Pale yellow-olive dubbing.
• TAIL: (Trailing shuck) Pale yellow-olive sparkle yarn.
• WINGS: Mallard quill segments tied spent.

Pale Morning Dun Thorax

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• TAILS: Light dun hackle fibers.
• BODY: Pale yellow-olive dubbing.
• WING: Medium gray turkey flat feather.
• HACKLE: Light dun wound through the wing and clipped on the bottom.

Pale Morning Dun Standard Dry

• HOOK: #16-#18, Tiemco 100 or Tiemco 5210.
• THREAD: Pale olive prewaxed 6/0.
• TAILS: Light dun hackle fibers.
• BODY: Pale yellow-olive dubbing.
• WINGS: Medium dun hackle tips.
• HACKLE: At least six turns of light dun hackle.

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Mike Lawson is the owner of the Henry's Fork Angler, on the Henry's Fork River, in Last Chance, Idaho.