Fly Fisherman Throwback: The Longest Hatch–II

Matching our major late-season mayflies.

August 29, 2023 By Ernest Schwiebert

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, John Voelker, 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 July 1977 issue of Fly Fisherman magazine. Click here for a PDF of the print version of "The Longest Hatch-II."

This is the second of two articles dealing with one of this country's most widely distributed and least-known mayflies. This portion deals with imitations and angling techniques. In our previous issue (Mid-Season), the author discussed the identification and life histories of the naturals. In that issue, the author also provided information on the distribution, emergence times and emergence dates of various species of this mayfly, which readers may wish to check when preparing to fish this hatch during the summer and fall. THE EDITORS.

Click here to read The Longest Hatch–I.

Thoughts of past Tricorythodes hatches lead to thoughts of many rivers, from the Otter and Battenkill and Lamoille in New England to the prolific spinner falls on the spring creeks of Oregon and northern California. There are boyhood memories of earlymorning hatches on the whippoorwill water of the Au Sable, and on the still flats of the Upper Pere Marquette. Other Michigan rivers such as the Manistee and Boardman and Rifle provided similar sport, and I remember late-summer mornings in the cottage at Wolf Lake, stealthily making breakfast while the others were still sleeping and the soft mirror of the lake was dark through the trees, waiting for the locust afternoons of August. Later there were early hatches at Ferdons and Wagon Tracks on the classic Beaverkill, and on the immense Delaware flats below Pepacton and Shinhopple. Sometimes we were baffled by the spinner falls, when we could see nothing on the water and were frustrated by the steady dimpling of the fish in the film. There was a boyhood morning when I stood waist-deep in Cairns Pool, surrounded by so many rising trout that I almost quit fishing in frustration, since we lacked the tiny hooks to match such hatches.

What are they taking? my father called.

They're taking those black-bodied mayflies, I shouted back, but it doesn't matter–we can't tie flies that small!

Smaller hooks were available in the years that followed, made largely for the circle of anglers that evolved on the limestone streams of central Pennsylvania, and we used them eagerly in imitating both terrestrials and the tiny Tricorythodes flies. These first hooks in sizes 22 and 24 were often brittle, but they allowed us to take selective fish that had frustrated us before, and fine hooks as small as sizes 26 and 28 are readily available now from first-rate shops.

It was fishing on the limestone streams of Pennsylvania that finally taught me the secrets of the Tricorythodes hatches, which, before those summer mornings with Ross Trimmer and Charles Fox, had produced a lot of frustrating moments. The mind sorts through a kaleidoscope of memories, remembering failures just at daylight on the willow-lined flats of the Upper Ausable in New York. Its fish bulged and dimpled softly in the film, and there were other trials on its sister river, the crystalline little East Branch below Keene Valley. Heavy spinner falls on the Little Lehigh in eastern Pennsylvania, and beautiful Falling Springs Run at Chambersburg, were the watercress classrooms where I had my first success with these diminutive mayflies. That led me to a Michigan pilgrimage, and our mixture of new fly patterns and cobweb-fine tippets helped to even the score for those boyhood failures in the cool mornings of July and August. Later I found excellent Tricorythodes hatches in northern Wisconsin, particularly in the Elodea shallows of the Namekagon and on the storied Brule at Cranberry Eddy. Although I seldom fish them, I have also encountered heavy spinner falls on the Pine and Loyalsock and Kettle in northern Pennsylvania, and on the still flats of the Paulinskill and Raritan and Musconetcong. Such Eastern rivers provide surprisingly good sport on the threshold of New York and Philadelphia.

But some of the best Tricorythodes fishing is unquestionably found on the lime-rich currents of Fall River in northern California, and on the remarkably fertile Henrys Fork of the Snake in Idaho. These streams are literally teeming with life, and their gently undulating weeds shelter vast populations of nymphs, crustaceans and larvae. Rich with dissolved oxygen, generated through photosynthesis by the rich growths of Elodea and fountain mosses and Chara, these streams are optimal habitat for the tiny Tricorythodes nymphs. Such nymphal populations clamber and forage in the root structures and subaquatic foliage of the weeds, and are principally herbivorous in their feeding.

A anatomical diagram of a trico nymph. — (Ernest Schwiebert illustration)

Before the early-morning emergence, the weeds are literally alive with these minute mayfly nymphs, and during the hatch they crawl toward the surface through their watery jungle-like habitat. The nymphs struggle clumsily, and a foraging trout can root them from the weeds while they clamber upward to hatch. The fish can gorge themselves on these minute insects, taking hundreds and hundreds of nymphs along a single growth of Ranunculus or Elodea, until their stomachs bulge like sausages.

Some nymphs reach the surface on the weeds themselves, while others drift to the surface after abandoning the shelter of the foliage. Since several species of Tricorythodes have been observed emerging from their nymphal skins before actually reaching the atmosphere, partially winged imitations of emerging nymphs are often effective during a hatch, although few anglers fish the nymphal stages.

Such neglect is partially due to the difficulty of fishing the nymph in the weedy habitat typical of Tricorythodes populations, and partially because of the skills needed to fish such tiny nymphs on fine tippets. Since the nymphs are incapable of swimming, they must be fished upstream with a dead-drift presentation. There are so many naturals available to the fish before and during a hatch that to fish such nymphs blind is pointless, and, as is the case in fishing the hatching duns or a subsequent fall of spinners, it is better to present a nymph imitation to a specific fish. Such trout can often be found working the borders of the weeds, flashing deep in the current when their bodies catch the light, or rooting in the weeds themselves. However, a fish taking the emerging nymphs just under the surface, or sipping them in the surface film itself, is much easier to take. The angler can fish to such trout in the same manner as a dry-fly presentation is made, placing his imitation of a hatching nymph just above the trout's feeding station. It is possible to sense the rate of drift of the tiny nymph, watch the fish that is working, and tighten when it rises again to take the artificial. Sometimes the fish is simply taking another natural, but sometimes you tighten and it is hooked. Fishing such minute nymphs in the film demands experience with tiny hooks and delicate tackle, and the development of a gentle touch.

More typical nymph-fishing tactics are possible on some Tricorythodes streams, particularly those that are more open with a stable bottom, or in spring-creek shallows where the fish are clearly visible. The tiny nymph is placed above a visibly feeding trout, and its rate of sink and drift is judged while watching the fish. When it moves to intercept something, and its open mouth shows white and closes, it is time to tighten. Such nymphing for fish that are clearly visible is both subtle and exciting.

During a typical Tricorythodes hatch, the male subimago flies emerge first. Once the hatches have fully started, the trout actually seem to anticipate their appearance at daylight. Before the first flies start coming, in the mist and dull light of early morning, the rivers seem lifeless. Yet it is possible to find a trout holding here and there in the growing light, almost waiting for the hatch and the spinner fall to follow. Such fish lie poised and obviously excited in their typical feeding lies, and they are easily frightened by a careless angler until the hatch begins.

The Tricorythodes flies have perhaps the most extensive period of emergence among the mayflies; fishable hatches may occur almost daily for as long as two to three months. Some observers have noted that hatches on our Eastern limestone streams usually occur at morning stream temperatures of 52-56° F. Summer hatches may occur earlier than normal so that the emergence is concentrated at optimal water temperatures, while hatching activity in the cooler months of September and October may come in late morning.

Once the tiny duns start coming well, the trout quickly lose their skittish character. Their feeding rhythms become remarkably steady as the numbers of hatching flies increase. Feeding activity may wane slightly as the swarm of mating adults gathers above the river, but then it waxes into gluttony with the spinner fall. Although soft riseforms are usually associated with such tiny insects, the brief character and incredible numbers of Tricorythodes flies often cause the fish to lose their typical caution. Their feeding rhythms grow urgent, until their greed makes them unaware of anything except the hatch, and they seemingly hang in the film to gobble the tiny flies. Sometimes a large fish will hold its mouth open and work upstream with its back visible above the current, greedily inhaling hundreds of the naturals.

The most dramatic example of this wanton feeding that I have seen took place on the Henrys Fork of the Snake. It was a bright August morning on the Harriman Ranch, and the early sunlight was alive with a blizzard of Tricorythodes flies. Their miniscule forms were everywhere, rising and falling for a half mile above the marshy islands, and the sun danced on their delicate wings. It was an unbelievable sight, and the river flowed smooth and still while the mating swarm continued its busy choreography above the weedy shallows.

The tiny spinners rose and fell in glittering swarms that hovered like mist over the Henrys Fork, and then they were gone and the morning sky was empty. There were millions and millions, I thought eagerly, and the fish should get started soon!

Suddenly, the river was alive with rising trout, and my waders were quickly encrusted with tiny spinners. There were several rainbows working against the grassy bank, and I took a half dozen so easily that I wondered why we considered the Henrys Fork a difficult river. Then I hooked a strong fish that took my entire fly line in a sullen run that fouled my leader in the Elodea, and broke the tippet like a cobweb.

The fish sure broke the spell, I thought.

While I retrieved the line, and patiently unraveled the leader from the Elodea, a huge trout started working in the channel downstream. Its behavior was surprising and I stopped to watch. The fish porpoised steadily, its dorsal and tail showing lazily while it prowled a backwater eddy. Soon it was taking the flies with a steady rhythm and rises that overlapped, its head projecting from the water and its white mouth showing. The fish ranged steadily along the bank, feeding greedily upstream for almost fifty feet, drifting back with an occasional rise to circle the backwater hungrily, and then turning back against the current for another feeding run. It was a big rainbow, perhaps six or seven pounds, and it ignored me completely.

He's got terrible table manners, I thought as I stood staring.

The trout repeated its feeding circuit for almost half an hour, taking hundreds and hundreds of tiny spinners that were pinioned in the surface film. Its jaws made a rolling wake, and its porpoising and bulging sent waves against the grass. Its final orgy carried it so close that I could see a heron soar behind its dorsal fin, and suddenly its feeding stopped, and the river flowed still and smooth.

Cover of the July 1977 issue of Fly Fisherman magazine; orange with a fly angler fishing a rocky stream. — This article originally appeared in the July (Late Season) 1977 issue of Fly Fisherman magazine.

You forgot to fish! I thought suddenly.

Vast swarms of mating spinners are common on the fertile rivers and spring creeks of our Western mountains. The entire winged life of these tiny mayflies is expended in the brief hours of a single morning. The subimago is hatched from the nymphs, the freshly emerged dun molts and becomes a fully adult spinner, the mating flight and egg laying in the river are completed, and the exhausted imago drops spent to the current in a spinner fall that can number in the millions. Rivers where the Tricorythodes flies are common hold enormous populations of nymphs, and a mating swarm that rises as much as thirty feet above the water can reach for miles along the stream. Looking into the early sun, the angler can see an astonishing sight–millions of wings catch the light, rising and falling restlessly in clouds that seem like microscopic bits of silvery confetti, and these clouds of spinners will ebb and undulate and flow with any delicate stirring of the wind.

Several factors in the feeding behavior of the fish are important in Tricorythodes season. There may be so many insects available that it can be difficult to get the fish to take an artificial, yet there are techniques for inducing such fish to rise.

Arriving well before the morning hatch is important, because a fisherman can observe the beginnings of the rise and pick the best fish to work on. The duns are relatively sparse when compared with the spinner fall to follow, and the fishing is still studied and calm. It seems foolish to waste time on a small fish. Experienced Tricorythodes regulars will watch the early stages of a hatch to locate a particularly good trout, and understand that the odds can be better in a secondary line of drift, since fewer insects crowd the currents there. It is profitable to fish out the entire hatching period, too, because the best fish are often found still feeding long after their lesser colleagues have gorged themselves and stopped.

But perhaps the best advice involves understanding that each fish will establish a feeding rhythm in Tricorythodes time, sipping and gobbling steadily in a timing dictated by its position, current speed, its sense of security, water temperature, the availability of the hatching flies or spinners, its size and agility and metabolic requirements, and its singular character. It is possible to observe its unique feeding rhythm and introduce an imitation into its line of drift so that the fly arrives at its taking point in sequence, perfectly timed to the rhythm of its riseforms. Such tactics will prove valuable through the full spectrum of the season, and are worth remembering on less prolific hatches than the Tricorythodes flies.

Early-morning rises to this hatch may occur on streams not usually associated with fishable populations of Tricorythodes flies. It should be remembered that all streams have small zones of microhabitat that can sustain these slow-water nymphs, and I have seen them on big Western rivers like the Snake and Yellowstone and Green. Their early-morning hatches often come from eddies and backwaters that shelter the Tricorythodes nymphs from their swift-flowing currents.

Several options are available in dressing imitations of the important Tricorythodes hatches. Male nymphs are active before daylight, and the male subimagoes are often found emerging in the last hour of the night. Since the duns often start to free their wings from the thoracic skin before reaching the atmosphere, tying imitations of these emerging duns can prove effective with hen-hackle points or a soft wing of smoky-dun marabou fibers.

Freshly hatched subimagoes are often slightly darker and duller in coloring than the spinners that follow, and display a smoky cast in their wings. Spinners are often partially spent when a mating swarm is finished, so both upright and fully spentwing patterns are useful on selective trout. Although there are parallels in the dressings designed to imitate the following species of Tricorythodes flies, different hook sizes are needed in such cases, since the naturals range from three to seven millimeters in length.

Conventional nymphs might be slightly weighted with a few turns of fine copper wire under the thorax, while emergers might be tied with a tiny tuft of gray marabou or down from the butt of a hackle feather instead of a typical wing case. Some fishermen prefer conventional hackle dressings to the no-hackle style, and others like hen-hackle spent wings instead of polypropylene. However, both the no-hackle dressing and spent poly-wing spinner have proved themselves.

An illustration of a trico mayfly, splayed out. — A T. stygiatus spinner, painted by the author, and shown here approximately fifteen times actual size. (Ernest Schwiebert illustration)

Trico Nymph Fly Recipes

Tricorythodes albilineatus

NYMPH (5.5 mm)

HOOK: Size 22 Mustad 94840.
NYLON: Dark brown.
TAILS: Brown partridge hackle fibers.
BODY: Dark brown with dorsal stripe of cream buttonhole twist.
RIBBING: Black goose-quill herl fiber.
GILLS: Medium-grayish wing quill sections coated with vinyl lacquer.
THORAX: Dark brown dubbing.
WING CASES: Dark blackish feather section with dorsal stripe of cream buttonhole twist.
LEGS: Brown partridge hackle fibers.
HEAD: Dark brown.

DUN (4 mm)