Behavioral Nymphing: Fishing Flies with Lifelike Action

This article was originally titled "Better Bug Behavior" in the March 2009 issue of Fly Fisherman magazine.

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When discussing nymphing, we usually consider fly size, shape, and color, as well as the best casts and rigs. An often overlooked—and important—element of nymphing is the behavior of the insects and the techniques needed to imitate them. Creating flies and fishing them so they behave more naturally is the premise behind what I call behavioral nymphing.

It’s been said many times that trout feed underwater 90 percent of the time, making nymphs, larvae, pupae, and crustaceans their largest food sources.

On many waters, trout feed heavily on mayfly nymphs, and anglers use a single fly, split-shot, and an indicator to present this food item. Anglers usually dead-drift the flies, wait for the indicator to pause or stop, and then set the hook.

Slack between the indicator and the fly in this situation can equal missed strikes. Furthermore, this approach lacks any imitation of life and movement in the fly.

Behavioral nymphing is more dynamic—the angler manipulates the nymph with rod movement and line control to swim the nymph, or to let it drift. With this subtle technique, you can simulate a living insect that is swimming, drifting helplessly, or rising and emerging. You can activate the nymph by twitching the rod tip, stripping line in quick or slow successions, and by stopping the rod during the drift to allow the fly to rise toward the surface.

Methods to slow and prolong the drift, or sink the nymph in a current seam, include stack mends and hump mends, while releasing line from your line hand. By varying and combining these techniques with standard dead-drift tactics, your nymphs appear more alive and dynamic.

Flies Alive

I prefer flies that look and behave naturally. On top of how you fish the fly, choosing the correct fly with the right materials is key. Ultra-buggy, impressionistic nymph designs are far more appealing to fish than realistic yet static and stiff patterns.

Natural furs like rabbit, hare’s mask, and squirrel work well because they produce bodies that undulate in the current. Soft-hackle collars—and palmered hackle to imitate legs, wings, and antennae—also increase movement in the fly.

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To make the materials move, sometimes I dead-drift the flies, and at other times I actively manipulate them, enhancing the current’s effect through both the line and rod action. Exactly how I manipulate the fly depends on water conditions, insect species and life stage, and how trout are feeding. Fished correctly, the flies come to life in front of the fish. Even when fish are not actively feeding, this tactic can trigger an “induced strike” or involuntary reaction.

In order to effectively imitate mayfly nymphs, it is important to understand the insect’s life cycle. After they hatch from eggs, mayfly nymphs increase in size until they reach maturity. Just before they emerge, their wingpads darken and the nymphs become more active. They emerge into adult mayflies underwater (anywhere from the streambed to the surface), on top of the water through the surface film, or out of the water on streamside rocks or vegetation. Many nymphs ascend to the surface by filling their abdomens with internal gases. This is often accompanied by the nymph swimming vigorously. These body undulations attract the attention of trout.

Versa Nymph

The Versa Nymph matches all mayfly species by merely altering the body, tail, and hackle color to match the naturals. I tie it in both half-dress (half-hackled collar) and full-dress (full-hackled collar) versions. The two-tone body suggests a nymph in transition, similar to the natural’s thorax that darkens as it reaches maturity and emergence.

The half-dress version has a partridge soft-hackle collar covering the sides and bottom of the fly but is open on the top. This adds soft-hackle action while making the color shades of the abdomen and thorax clearly noticeable.

I use the half-dress Versa Nymph in slower water where fish have more time to inspect a fly for exactness. The full-dress Versa Nymph is best in riffles and more turbulent water.

For mayfly emergers, I tie my Transition Flymph with a full hackle collar and with adult mayfly body coloring in the thorax to imitate the dun’s body, legs, and unfurling wings—it’s half nymph, half dun. These three life cycle patterns can be adapted by altering the hook size, color, weight, and behavior (how you fish them) to match any and all mayfly species.

Wet your rabbit fur dubbing to check the desired color as it will darken when you fish it. Also, match the hackle color, and hook size, to the natural.

Weighting

Fish nymphs that imitate specific stages of the mayfly life cycle at the appropriate depth. Your fly must be in the strike zone to be pursued by the fish, so the weight of the nymph is often as important as the size, shape, and color.

I prefer to weight my nymphs progressively, which means varying the weight based on the insect life stage; the depth and speed at which you want the fly to drift or rise; and the water’s depth, speed, and clarity. Unweighted or lightly weighted mayfly emergers drift just under the surface. For these flies I use fine copper wire underbodies wrapped around the base of the hook. For heavier nymphs, tie lead-free wire underbodies followed by brass and then tungsten bead thoraxes or heads. Split-shot is beneficial but not always necessary if proper mending techniques are employed with weighted nymphs.

Point Fly Dropper

Fishing two or three nymphs at one time gives you a distinct advantage because it allows you to imitate two or more nymph stages simultaneously. For example, a three-fly nymph rig could imitate an immature streambed nymph, a mature rising nymph, and an emerger—all in the same cast. In this setup, use a weighted middle nymph so all three nymphs ride at their intended depths in the water column.  However, don’t feel as though you have to fish multiple nymphs if you can’t control them. It’s far better to control one fly well.

Fishing a single nymph allows maximum control of the fly, while mixing drag-free presentations with active presentations directed at only one life stage. Two- or three-fly rigs allow you to counterbalance the flies, and cover all the nymph life stages with multiple patterns.

Naked Nymphing

I like to vary the action of the nymphs I’m fishing. And I find that fishing without a strike indicator gives me better control of my flies. An indicator acts as a buoy, allowing you to fish only a predetermined depth. Also, a fish may take the fly and release it without the indicator moving. By fishing without an indicator, you have better contact with the fly, sense the fly’s position, and react to strikes instantaneously.

I use a handling technique that allows a slight amount of slack line when my nymphs are drifting, but also lets me feel the strike. In order to detect strikes, I fish the nymphs three ways: tight through the drift, nearly tight, or with varying degrees of slack from mending—but always under control.

I use hump or stack mends for dead-drifting. Then I activate, swim, and manipulate the fly with line strips or lifts and drops of the rod tip. If the fly begins dragging, I mend to prolong the drift. This causes the fly to slow and drop momentarily until the line begins to tighten up again. In appearance, this line mending and checking causes the fly to drop and rise at will, giving your nymphs a swimming action.

Some of the methods for actively fishing mayfly nymphs include swinging the fly from deep to shallow, sinking the fly with mends, and active retrieves. Examples of active retrieves include: stripping line, raising the rod tip to lift the fly (the Leisenring lift), rod tip twitches, and combinations of all of these. The idea is that, through conscious combinations of mending, dead-drifting, swinging, and active retrievals, your fly reaches fish in the most natural and attractive way.

On the Stream

Knowing how individual species emerge is important, but you must also consider the trout’s reaction to the natural flies on the stream. Elements such as weather and water temperature play a large part in the speed of emergence during the hatch. Fish your flies more slowly when wet, cold days stiffen the nymphal exoskeleton, delaying the emergence of the dun. Warm weather promotes quick emergences, and flies can be fished more actively.

Life Cycle Nymph Rig

Know Your Mayfly Nymphs

Different nymph species have unique habitats and emergence behaviors. Understanding them can help you fish them realistically.

Swimmers

Baetis. Baetis nymphs are quick swimmers, and they undulate to propel themselves toward the surface. Use some action to swim your nymphs toward the surface during the emergence. Behavioral drift (dead-drift) occurs early and late in the day. Baetis are available year-round on stable streams and exhibit particularly good emergences on wet, cool days.

Gray Drakes. Gray Drake duns emerge near streambanks. Swim your nymph imitations toward the streambank with aggressive movement, like a streamer. The Western species hatches during the summer through September.

Crawlers

PMDs and Sulphurs. Western Pale Morning Duns and Eastern Sulphurs are both considered crawlers, although they swim to the surface to hatch. Fish the nymphs aggressively—with a fast-swimming presentation—if the trout are rising. Otherwise, use a slow, natural rise to entice the fish. These species hatch from June through September.

Western Green Drakes. Fish lightweight Versa Nymphs or Transition Flymphs as the duns emerge, because the natural nymphs often swim from the stream bottom to the surface several times before the hatch begins. Duns emerge from mid-June to August, and into September.

Flavilinea. Flav nymphs are typically available from midsummer through October. Hatches occur in calm water, such as pools and eddies. Use a lightweight nymph or emerger pattern fished smoothly toward the surface.

Clingers

March Browns. These clingers swim to the surface to emerge. The nymphs are especially important because they become active days before the hatch begins, usually in mid to late May as water temperatures increase. In the weeks prior to the hatch, fish your nymphs deep. As the hatch progresses, fish your nymphs shallower in the water column.

Light Cahills. Usually these nymphs are productive only shortly before the hatch begins, as the naturals are protected by clinging to streambed rocks. Eastern hatches occur from late June through July.

Epeorus (Quill Gordons). Epeorus nymphs are among the first large mayflies of the year to hatch. They emerge from their nymphal shucks on the stream bottom and ascend to the surface as adult duns. A Transition Flymph fished from deep water to the surface imitates this emergence.

Burrowers

Hexagenia. Hex nymphs spend most of their lives burrowed into the mud where the trout can’t get them. During emergence—usually at sunset and through the night—the large nymphs swim actively toward the surface, and swimming flies are just as effective (at times) as emergers and drys. In the dark, tight-lined nymphs are easier to fish than drys. The nymphs are slow swimmers and make large, cumbersome movements. Fish them toward the surface with a slow but constant rise of the rod tip and periodic twitches. Hatches occur May through June in the West and Midwest, and can last up to two months.

Brown Drakes. Like Hexagenia, these nymphs swim strongly to the surface to emerge. Use the same swimming presentations in the late evening. Emergences occur from late May through early June in the West.

Eastern Green Drake. Green Drakes emerge in late May through early June in Pennsylvania and New York. In the evening, before the hatch begins, fish your nymph deep. As the hatch approaches, add some action as the naturals become more active. Try a stack-and-slack swing from deep up to a foot or so below the surface. This works best at dusk. During the peak of the emergence, fish a Green Drake Transition Flymph inches below the surface with rod tip twitches or short strips to imitate the nymph struggling to free itself from the shuck.

Stack-and-Slack Swing

Make a straight-line cast across and upstream of the trout. When the line lands on the water, immediately make two stack mends on either the right or left side of the line, and then drop the rod tip to the water to create slack and allow the fly to sink. When the line tightens, the fly will swing and rise in front of the fish. Also experiment with small line strips or twitches of the rod tip to impart more action to the fly.

Guaranteed Hook-Down Knot

A little-discussed, but highly important matter is the fly’s position underwater. A nymph attached with a clinch knot either hangs vertically from the knot, or rides upside down (hook point up) because of the weight of the hook shank. This is fine for a nymph tied “in the round” because the fly looks the same from all angles, but for nymphs that have a designated top and bottom, the fly should ride appropriately. Real nymphs, particularly swimming nymphs, swim right-side up. To achieve a hook-down drift, use the guaranteed hook-down knot advocated by Fox Statler.

PMD/Sulphur Nymph Life Cycle

Transition Flymph (emerger)

HOOK: #14-18 1XL nymph.
THREAD: Light yellow 8/0.
TAIL: Pheasant tail.
RIB: Copper wire.
ABDOMEN: Pheasant tail.
THORAX: Pale yellow Hareline dubbing.
HACKLE: Light tan partridge.

Versa Nymph (deep)

HOOK: #14-18 1XL nymph.
HEAD: Gold bead.
THREAD: Brown 8/0.
TAIL: Brown partridge.
RIB: Yellow wire.
ABDOMEN: Tan Hareline dubbing.
THORAX: Rusty brown Hareline dubbing.
HACKLE: Brown partridge.

Versa Nymph

HOOK: #14-18 1XL nymph.
THREAD: Brown 8/0.
UNDERBODY: Small wire.
TAIL: Brown partridge.
RIB: Yellow wire.
ABDOMEN: Tan Hareline dubbing.
THORAX: Brown Hareline dubbing.
HACKLE: Brown partridge.

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Allen McGee is the author of Tying & Fishing Soft-Hackled Nymphs (Frank Amato Publications, 2007). He lives in Atlanta, Georgia.