The PMD Comparadun in size 16 to 18 is listed on 72 of the 92 river pages on this site, more than any other single mayfly dry, and that tells you what the pale morning dun is: the summer mayfly that every Western trout river shares. Seventy-eight rivers carry PMDs in their hatch charts, from the desert tailwaters of Arizona to the cutthroat streams of Yellowstone, and the peak runs from June on the low, warm water to August in the high country. It is not the biggest mayfly and not the most exciting. It is the dependable one, the hatch you can plan a July trip around and expect to find, and the one that teaches more anglers about emergers and cripples than any other bug.
Ephemerella, and the two species behind one name
PMDs are Ephemerellidae, genus Ephemerella. Two species make up the Western hatch: Ephemerella excrucians (long known as Ephemerella inermis, and still called that in older books) and Ephemerella dorothea infrequens. They overlap in range and season and look alike on the water: a size 16 dun with a pale yellow to yellow-olive body, sometimes with a pinkish or orange cast on some rivers, and pale gray wings. The dorothea insect runs a size smaller, and the size 18 in the fly lists is for it. The spinner is rusty brown, which is why a Rusty Spinner belongs in the box even though the river pages here list only duns and emergers.
The nymph is a crawler, stout and dark, that lives in gravel and weed in moderate current. It is a poor swimmer, and when it emerges it drifts a long way, which is the key fact about fishing this hatch.
Why cripples and emergers outfish the dun
A PMD nymph rises to the surface and has to break through the film and shed its shuck, and a lot of them fail. They drift with the shuck stuck to the abdomen, wings half out, unable to fly, and trout learn very quickly that a stuck PMD is easier to catch than one that is about to leave. On a heavy hatch on the Missouri or the Henry's Fork, a perfect high-floating dun will be refused by fish after fish while a cripple is eaten on the first drift.
The fly lists reflect this. The Sparkle Dun PMD (33 rivers) is a Comparadun with a trailing shuck. The CDC PMD Emerger (19 rivers) rides in the film with a CDC wing. The PMD Cripple and the Harrop PMD patterns listed for the Henry's Fork, Silver Creek, Hat Creek, the Frying Pan, and the South Platte sit even lower. The No-Hackle PMD on Silver Creek and Hat Creek is a dun for the flattest water, where a hackled fly looks wrong. The Green lists a Split Case PMD, a nymph with the wing case opening, for fish taking emergers a foot under the surface. Carry all three stages: a Pheasant Tail or Hare's Ear in 16 for the nymph, an emerger or cripple, and the Comparadun for fish that are actually taking duns.
When in the day
The name is only half right. PMDs do hatch in the morning, but on most rivers the emergence runs from late morning into early afternoon, and on cool or overcast days it can go on all afternoon. On hot days in July and August the hatch shifts earlier, and on the tailwaters with cold releases it can be almost a midday event. The spinner fall comes in the evening, often around dusk, and the rusty spinners fall on the riffles and drift into the pools below. On rivers like the Missouri and Bighorn, the evening spinner fall can be better fishing than the morning hatch because the fish are less pressured.
Where and when: a peak-month map from the river charts
The 78 river matrices sort into three clear groups by water type and elevation:
| Peak months | Water type | Rivers on this site |
|---|---|---|
| June and July | Tailwaters and low-elevation rivers | Missouri, Bighorn, South Platte, Blue, Eagle, Provo, Middle Provo, Strawberry, Green (WY), Shoshone, Firehole, Boise, the California and Nevada rivers (Upper Sacramento, Truckee, Owens, East Walker), and the Oregon coastal rivers |
| June through August | Cold tailwaters and spring creeks with long seasons | Henry's Fork, Silver Creek, Frying Pan, Taylor, Gunnison, Colorado, Arkansas, Roaring Fork, Big Wood, Teton, Metolius, Yakima, Hat Creek |
| July and August | Freestones and high-elevation rivers | Madison, Big Hole, Yellowstone, Gallatin, Bitterroot, South Fork Snake, Snake (WY), Lamar, Gibbon, North Platte, the Utah freestones (Logan, Weber, Duchesne, Uinta), and the New Mexico mountain streams |
The Green River below Flaming Gorge peaks in July alone, and the two Arizona desert streams, Oak Creek and the Verde, get theirs in June before the water gets too warm.
Fishing the hatch
- Before rising starts, fish the nymph. A size 16 Pheasant Tail dead-drifted through the riffle above the flat water, with a light indicator or under a dry, takes fish that are eating nymphs drifting toward the surface.
- When the first noses show, fish the emerger, not the dun. Grease the leader to within a foot of the fly and let it hang in the film.
- Watch the rise form. A splashy rise with the fish's nose clearing the water is a dun eater; a slow bulge with just the back showing is an emerger eater; a barely visible sip in the slick is a cripple or spinner eater.
- Use 5X in the riffles, 6X on the flats of the Henry's Fork, Silver Creek, and the Missouri.
- Stay for the evening. Come back to the same water at dusk with a Rusty Spinner in 16 and fish the tailouts.
A practical PMD box for any Western river
A dozen PMD Comparaduns in 16, a half dozen in 18, a dozen Sparkle Dun PMDs in 16, six CDC PMD Emergers, six cripples, six Rusty Spinners, and a card of Pheasant Tails in 16. That covers every river above all summer. Most of the tailwaters and spring creeks in the table are special-regulation water, so check the state fish and game agency before you go. And if you are on the Henry's Fork or the Provo in June, the PMD hatch overlaps the green drake, which is the one insect the fish will drop a PMD for.