Understanding the hatch: matching flies to the Pale Morning Dun

I. The Pale Morning Dun Life Cycle:

Mayflies undergo incomplete metamorphosis, meaning they have three distinct life stages: egg, nymph, and adult (with two sub-stages in the adult phase).

A. Egg Stage:

• Description: PMD eggs are typically small (around 0.3-0.5 mm), oval or slightly elongated, and range in color from pale yellow to light brown. They are usually deposited by the female adult either on the water's surface or just below it. Some species may crawl underwater to deposit eggs on submerged rocks or vegetation.

• Duration: The incubation period for PMD eggs varies significantly depending on water temperature. In warmer waters, hatching may occur in a few weeks, while in colder waters, it can take several months, often overwintering.

• Angling Significance: While anglers rarely directly target trout feeding on eggs, understanding where and when eggs are deposited can provide clues about upcoming nymph hatches. Heavy hatches the previous year can indicate a strong nymph population.

B. Nymph Stage (Subaquatic):

• Description: PMD nymphs are slender and agile, belonging to the "crawler" nymph classification. They possess the following key characteristics:

  • Size: Typically range from size 14 to 18 on standard fly hooks.

  • Color: Vary depending on the instar (growth stage) and water conditions, but generally range from pale yellow, cream, olive-yellow, to light tan. They often darken as they mature.

  • Gills: They have flattened, plate-like gills along the sides of their abdomen, usually seven pairs. These are crucial for oxygen uptake.

  • Tails: They possess three distinct tails, although the median tail may be shorter and less prominent in some species.

  • Wing Pads: As they mature, wing pads become increasingly visible on their thorax, indicating their impending emergence.

  • Behavior: PMD nymphs are often found clinging to the undersides of rocks in moderate to swift currents. They are detritivores and algae grazers.

• Duration: The nymph stage is the longest part of the PMD life cycle, lasting from several months to over a year, depending on the species and water temperature.

• Angling Significance: Nymphs are a constant food source for trout. Fishing nymph imitations effectively, especially during the pre-hatch period, can be highly productive.

C. Adult Stage (Terrestrial):

The adult stage is further divided into two sub-stages: the dun and the spinner.

1. Dun (Subimago):

Description: The dun is the first winged stage of the mayfly. It emerges from the nymphal shuck (exoskeleton) at the water's surface. Key characteristics include: Size: Typically matches the nymph size, ranging from size 14 to 18. Color: Generally duller than the spinner, with colors ranging from pale yellow, cream, olive, to light tan. Wing color is often a smoky gray or translucent with a milky or cloudy appearance. Wings: Possess upright, opaque wings with noticeable veination. They have two pairs of wings, although the hind wings are significantly smaller. Tails: Retain the three tails of the nymph, although they may be slightly shorter. Behavior: Duns are weak fliers and spend a period of time on the water's surface drying their wings before flying to streamside vegetation. This "drying" period makes them vulnerable to feeding trout.

Duration: The dun stage typically lasts from a few hours to a day, during which the mayfly's internal organs mature for reproduction. Angling Significance: The dun emergence is often the peak of dry fly fishing activity. Trout will actively feed on these vulnerable insects drifting on the surface.

2. Spinner (Imago):

Description: After molting from the dun, the mayfly becomes a spinner. This is the sexually mature adult stage. Key characteristics include: Size: Similar to the dun, size 14 to 18. Color: Typically more vibrant and translucent than the dun. Body colors can range from clear yellow, rusty orange, to reddish-brown. Wings become clear and glassy. Wings: Clear and translucent with less noticeable veination. The hind wings are significantly reduced or absent in some mayfly families, but PMDs retain two pairs, though the difference in size is still apparent. Tails: Usually longer and more delicate than the dun's tails. Behavior: Spinners gather in swarms over the water, often in the late afternoon or evening. Males perform elaborate mating flights, and females fly into the swarm to mate. After mating, the females return to the water to deposit their eggs, often fluttering on the surface or dipping their abdomens. Spent spinners (dead or dying after egg-laying) lie flat on the water's surface.

Duration: The spinner stage can last for a few days, but individual spinners will only be actively involved in mating and egg-laying for a shorter period. Angling Significance: Spinner falls can trigger intense feeding frenzies as trout gorge on the helpless insects on the surface. Matching the spinner color and profile is crucial during these events.

II. Choosing Flies to Match the PMD Life Cycle for Trout:

To effectively target trout feeding on PMDs, you need a selection of flies that accurately imitate each stage of their life cycle. Here's a breakdown of fly choices:

A. Matching the Nymph Stage:

• Key Characteristics to Imitate:

  • Size: 14-18

  • Color: Pale yellow, cream, olive-yellow, light tan

  • Profile: Slender, slightly flattened body

  • Movement: Subtle, crawling action

• Effective Nymph Patterns:

  • Pheasant Tail Nymph: A classic and versatile pattern that imitates the slender profile and coloration of many mayfly nymphs. Use variations with different bead colors (gold, copper) and body materials to match specific PMD shades.

  • Hare's Ear Nymph: Another excellent general mayfly nymph imitation with a buggy appearance that trout find appealing.

  • PMD Specific Nymphs: Patterns tied with specific PMD characteristics in mind:

    • Barr's Emerger: Can be fished as a nymph or a rising emerger.

    • Quill Nymph: Imitates the segmented body of a mayfly nymph.

    • Two-Bit Hooker: A weighted nymph that sinks quickly.

    • Juju Baetis (in PMD colors): While technically a Baetis imitation, the slender profile and coloration can work well for PMD nymphs.

  • Soft Hackle Nymphs: These patterns, when fished with a slight twitch, can imitate the movement of a drifting or emerging nymph.

• Fishing Techniques: Fish nymph patterns using various techniques, including:

  • Dead-drifting: Allowing the nymph to drift naturally with the current.

  • Indicator nymphing: Using a strike indicator to detect subtle takes.

  • Euro nymphing (tightline nymphing): A direct contact method for precise drift control.

  • Swinging nymphs: Presenting the nymph across the current.

B. Matching the Dun Stage:

• Key Characteristics to Imitate:

  • Size: 14-18

  • Color: Pale yellow, cream, olive, light tan

  • Profile: Low-riding on the water's surface

  • Wings: Upright, opaque, smoky gray or milky

  • Tails: Three distinct tails

• Effective Dry Fly Patterns (Dun Imitations):

  • Pale Morning Dun Comparadun: A highly effective pattern with a sparse deer hair wing that sits low on the water and imitates the dun's profile well.

  • Pale Morning Dun Quill Body: Utilizes stripped peacock herl or other quill materials for a segmented body.

  • Pale Morning Dun Sparkle Dun: Features a trailing shuck of Antron or Z-lon to imitate an emerging dun.

  • Pale Morning Dun Parachute: The parachute hackle provides excellent visibility and a good footprint on the water.

  • Pale Morning Dun Thorax Dun: A realistic pattern with hackle tied horizontally across the thorax.

  • CDC PMD Emerger: CDC (Cul de Canard) feathers create a very natural and buoyant fly that imitates a dun struggling to emerge.

• Fishing Techniques:

  • Dead-drifting: Present the dry fly with a drag-free drift over rising fish.

  • Upstream casts: Position yourself below rising fish and cast upstream, allowing the fly to drift naturally into their feeding lane.

  • Mending line: Adjust your line to eliminate drag and ensure a natural presentation.

C. Matching the Spinner Stage:

• Key Characteristics to Imitate:

  • Size: 14-18

  • Color: Clear yellow, rusty orange, reddish-brown (body); clear, glassy wings

  • Profile: Flat on the water (spent spinners) or upright wings (mating spinners)

  • Wings: Clear and translucent

  • Tails: Long and delicate

• Effective Dry Fly Patterns (Spinner Imitations):

  • Rusty Spinner: A classic pattern with a rusty brown or orange body and clear wings (often made of Zelon or CDC).

  • PMD Poly Wing Spinner: Uses a synthetic wing material that imitates the clear wings well.

  • CDC Spinner: CDC wings provide a delicate and realistic appearance.

  • No-Hackle Spinner: Relies on the body and tails for the silhouette, often very effective for picky fish.

  • Spent Partridge Spinner: Partridge hackle laid flat imitates the spent wings.

• Fishing Techniques:

  • Dead-drifting: Present the spinner imitation drag-free over fish feeding on spent spinners.

  • Targeting rising fish: Look for subtle rises during spinner falls, as trout often sip these low-floating insects.

  • Varying presentation: Experiment with different drifts and retrieves if fish are being selective.

III. Key Considerations for Fly Selection:

• Size Matters: Always try to match the size of the natural insects you observe on the water. Carry a range of sizes in your PMD imitations.

• Color Accuracy: While exact color matching isn't always critical, having flies in the general color range of the PMDs you see is important.

• Profile is Crucial: Trout are often very attuned to the silhouette of the insects. Choose flies that accurately represent the body shape and wing configuration of the natural.

• Emergence Patterns: Pay attention to how the PMDs are emerging. Are they struggling on the surface? Are they quickly flying away? This will influence your fly choice (emerger patterns vs. fully winged duns).

• Water Conditions: In faster, riffly water, trout may be less selective, and more general patterns can work. In slower, clearer water, precise imitations and delicate presentations are often necessary.

• Time of Day: Spinner falls often occur in the late afternoon or evening. Be prepared with spinner patterns during these times.

• Local Variations: PMD color and size can vary slightly from river to river. Observe the naturals on your local waters to fine-tune your fly selection.

IV. Tips for Success:

• Observation is Key: Before you even cast, spend time observing the water. Look for rising fish, emerging insects, and the behavior of the naturals.

• Start with Nymphs: If you don't see surface activity, try fishing nymph imitations in likely holding water.

• Match the Hatch: When you see duns emerging or spinners falling, switch to appropriate dry fly patterns.

• Presentation is Paramount: A drag-free drift is essential for fooling trout, especially with dry flies.

• Be Prepared: Carry a well-organized fly box with a variety of PMD imitations in different life stages, sizes, and colors.

• Don't Be Afraid to Experiment: If fish are refusing your initial offerings, try different patterns, sizes, and presentations.

By understanding the life cycle of the Pale Morning Dun mayfly and carefully selecting flies that imitate each stage, you'll significantly increase your chances of success when targeting trout during these important hatches. Remember that observation and adaptation are crucial elements of effective fly fishing. Good luck on the water!