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Mayfly

Pale Morning Dun

Ephemerella excrucians · species

A dependable mayfly match when trout key on pale nymphs, emergers, duns, and spent spinners.

Overview

About Pale Morning Dun

Pale Morning Dun refers here to Ephemerella excrucians, a spiny crawler mayfly in the family Ephemerellidae. It is found across Canada and the continental United States, making it a familiar hatch for Idaho anglers.

Also known as: PMD

Life Cycle

Eggs

Female mayflies lay hundreds to thousands of eggs either in or near the water. These eggs eventually sink to the stream bottom, where they will develop.

Nymph

Nymphs spend the majority of their lives on the stream bottom. They feed and grow, undergoing several molts as they mature.

Emerger

As the nymph matures, it rises to the water's surface. At this point, the adult form begins to hatch from its nymphal shuck.

Dun

The newly emerged adult, known as a dun, rests on or just above the water's surface. It allows its wings to dry and harden before further transformation.

Spinner

Mated adult mayflies, now in their spinner stage, ascend into the air. This aerial phase is primarily for mating and reproduction.

Egg Laying Spinner

After mating, the female spinner returns to the water's surface. She carefully deposits her eggs to ensure the continuation of the species.

Spent Spinner

Following egg-laying, adult mayflies die. Their spent bodies often float on the water's surface, becoming an easy meal for fish.

Stages: Anglers commonly fish the nymph, emerger, dun, and spinner stages. As a mayfly, it develops underwater before emerging to the winged dun stage, then molts again into a spinner.
Emergence cues: Look for activity during typical mayfly emergence periods in the warmer part of the fishing season, especially once flows and water temperatures stabilize; hatches are often most noticeable from late morning into afternoon, with spinner falls later in the day.
Behavior: Nymphs are active on the bottom and in the drift, emergers rise through the water column, duns ride the surface as they dry, and spinners return spent with flat wings after mating.

How to Tie Pale Morning Dun Patterns

Nymph

Fly Tying Tutorial: Hogan's Two Tone (Pale Morning Dun Nymph)

Loon Outdoors

Materials

Hook16Firehole 516 nymph jig hook
Bead3/32ndCopper slotted bead
Thread #18/0Rusty Brown
Thread #28/0Light Cahill
TailWood Duck Mallard Flank
RibRootbeer Midge Flash, Copper Brown small uni wire
Body8/0Rust Brown
TopPrince nymph brown Goose Biot
Abdomen8/0Light Cahill
Wing CasePrince Nymph Brown Goose Biot
LegsOlive Brown Antron/Poly Yarn

Emerger

Fly Tying Tutorial: Hogan's Simple PMD Emerger

Loon Outdoors

Materials

Hook16 or 18Tiemco 3761 Standard Wet Fly Hook
Bead3/32ndCopper
Thread #1Uni Thread - Rusty Brown
Thread #2Uni Thread - Light Cahill
TailPheasant Tail
Body #1Uni Wire - Small Copper Brown
Body #2Ice Dub - Pheasant Tail
LegsMallard Flank

Dun

PMD Trigger Point Usual

tightlinevideo

Materials

Hook#12-18Fulling Mill 5050
Thread10/0Pale yellow Veevus
DubbingPale Yellow beaver-fur
Medium Caddis Grey EP Trigger Point FibersTail & wing
DubbingBody - Pale Yellow beaver-fur

Egg Laying Spinner

Yellow PMD Spinner Dry Fly with Eric Austin

Traditional Flies and Dries

Materials

Standard dry fly hook TMC100#16-20or equivalent
ThreadYellow
Microfibbets4-6light dun, splayed; or 6-8 light dun hackle strands
CDC feathers2light dun, mounted back to back, posted up, and split semi-spent
PMD dubbing

Spent Spinner

Rusty Spinner Spent PMD Fly Tying Video

Caddis Fly Angling Shop

Materials

Tiemco 100#16Hook
Semperfli Yellow Nanosilk50DThread
Hareline CDLGinger SpeckledTails
Hareline Turkey Biot QuillBrownAbdomen
Hareline Micro Fine Dry Fly DubSulphur YellowAbdomen
Zap-A-GapAbdomen
Hareline Super Fine Dry Fly DubTanThorax

Where It Hatches

Pale Morning Dun

One species, multiple rivers.

River

Fly Patterns

Pheasant Tail Nymph#12-22
PMD Comparadun#16-20
PMD Emerger#16-20
PMD Sparkle Dun#16-20
Soft Hackle#12-18

Angler Notes

Why it matters: PMDs are a classic match-the-hatch bug because trout may feed on them in every phase, from drifting nymphs to vulnerable emergers, floating duns, and spent spinners.
Imitation tips: Carry a simple progression: a slim to slightly robust PMD nymph, a soft-hackle or cripple/emerger, a clean upright-wing dun, and a low-profile spinner. Keep colors in the pale yellow, cream, and light olive range, and adjust size before changing pattern style.
Key life stages: nymphemergerdunspinner
Presentation: Start below the surface with a dead-drift nymph through riffles and seams. When fish begin showing near the top, switch to an emerger or cripple in the film; move to a dun for steady surface takes, and finish with a flat-drifting spinner when trout key on spent adults.

Identification

Key features: A compact mayfly with a crawler-style nymph and pale-winged adult; anglers usually notice the slender profile, upright wings on duns, and spent-wing spinner silhouette.
Size: Typically imitated in moderate mayfly sizes, often around #14–18 depending on water and hatch.
Coloration: Usually pale yellow to creamy olive tones, with adults often showing light bodies and pale gray to yellowish wings.
Similar bugs: Flav / smaller PMDPale Evening DunBlue-Winged OliveLight Cahill-type mayflies

Habitat

Water types: RiversStreamsRiffle-to-run sections
Substrate: Commonly associated with rocky or mixed gravel-and-cobble bottoms where crawler nymphs can hold among substrate and current seams.
Conditions: Most relevant in moving water with good oxygen and a steady aquatic insect community; trout often key on them in clear to moderately stained conditions when mayflies are concentrated in the drift or on the surface.