Pale Morning Duns
This name used to refer to two now defunct species, Ephemerella inermis and Ephemerella infrequens. The inermis mayflies were discovered to be the same species as Ephemerella excrucians and now they bear that scientific name. The infrequens species was recently reclassified as a subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.) of Ephemerella dorothea.
Anglers usually shorten the Pale Morning Dun hatch to the PMD hatch. The PMD is one of the top mayflies referenced in fly shops and hatch charts across the West, although they occur in the Midwest as well. Given this popularity, it is surprising that so many fly patterns meant to imitate PMDs, and so many fly tying materials (especially body materials) designed around them, are the wrong color: yellow. Every Ephemerella excrucians specimen I've sampled has been a pale green that couldn't even slightly be mistaken for yellow. The only place I've seen this reflected in imitations was in dubbing sold under René Harrop's name for the PMDs on the Henry's Fork, which has a proper greenish tint.
Like most common names, "Pale Morning Dun" can refer to more than one taxon. They're previewed below, along with 6 specimens. For more detail click through to the scientific names.
These are pretty much always called Pale Morning Duns.
Ephemerella dorothea infrequens
(formerly Ephemerella infrequens
), together with its often smaller and later hatching sibling Ephemerella excrucians
, make up the most important Western hatches. They go by several common names but are best known as Pale Morning Duns (PMD's). They are rivaled only by the many baetid species that typically bookend them. In terms of availability, consistency and abundance (not to mention their convenient timing and preference for beautiful weather), they have no rival. They can run in size from a large 14 to a small 16 and various shades of illusive yellowish creams, sulfurs, and even yellowish greens, depending on the system they inhabit.
This taxon used to be considered the separate species Ephemerella infrequens
, but entomologists now regard it as a subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.)
together with the small eastern Pale Evening Dun hatch Ephemerella dorothea dorothea
. There is another related listing of significance common in California and the Southwest that has undergone revision. The large (often exceeding 10 mm) Ephemerella mollitia
is now considered synonymous with d. infrequens
While it is not the normal policy of TroutNut to list subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.)
as separate taxa, d. infrequens
and d. dorothea
are so important and distinct from each other in terms of geography, appearence, and angling tradition that they warrant an exception.
Ephemerella dorothea infrequens (Pale Morning Dun) Mayfly Nymph
View 2 PicturesHabitat: Shallow riffle over cobble; approx. 1 ft. deep
Size: 8.5 mm. Mature specimens have been captured as large as 10.5 mm.
Emergence schedule: Variable - starting as early as mid March and lasting as late as early June, depending on the year. Usual duration is at least several weeks or more.
Dun Association: Body is elusive pale creamy yellow w/ orange highlights, cream legs and tails, and dun wings
Specimen status in photo: Preserved
Collection method: Kick net
Comments: Extremely common in samples taken from this location. It's color in life was very close to as depicted in the photo; except for the gradual darkening of the abdominal segments as they progress posteriorly, which has been accentuated somewhat by the effects of preservation. Adult association is based upon capture of this taxon at various stages of emergence including: darkened wingcases, split thoraxic notums, and partially ecloded or ''stillborn (Stillborn: In fly fishing, a stillborn insect is one which got stuck in its nymphal or pupal shuck during emergence and floats helplessly on the surface instead of flying away. It is a specific class of cripple, although it is sometimes used interchangeably with that term.)'' specimens.
Collected March 21, 2011
from in Added to Troutnut.com by on November 1, 2011
These are pretty much always called Pale Morning Duns.
For trout (if not anglers), this single species is arguably the most important mayfly in North America. In terms of sheer numbers, breadth of distribution and hatch duration, it has a good argument.
or Pale Morning Dun usually follows its larger sibling Ephemerella dorothea infrequens
with which it shares the same common name. What it often lacks in size by comparison is made up for with it's duration, often lasting for months with intermittent peaks. This close relationship with infrequens
has led many anglers to confuse Pale Morning Dun biology with that of the multivoltine (Multivoltine: Having more than one generation per year.) Baetidae
species, having disparate broods that decrease in size as the season advances. Sharing the same common name has not helped to alleviate this misconception.
Until recently, Ephemerella excrucians
was considered primarily an upper MidWestern species of some regional importance commonly called Little Red Quill among other names. Recent work by entomologists determined that it is actually the same species as the important Western Pale Morning Dun (prev.Ephemerella inermis
), and the lake dwelling Sulphur Dun of the Yellowstone area, (prev.Ephemerella lacustris
). Since all three are considered variations of the same species, they have been combined into excrucians
, being the original name for the type species reported as far back as the Civil War. Angler speculation had simmered for some time that the stillwater loving Ephemerella lacustris
was much more widespread, inhabiting more water types then previously thought and could account for many large sulfurish ephemerellids found in still to very slow water locations throughout the West. With the revisions, this discussion is now moot.
variability in appearance, habitat preferences, and wide geographical distribution are cause for angler confusion with the changes in classification. They can be pale yellow 18's on a large Oregon river, creamy orange 14's on western lakes and feeder streams, large olive green on CA spring creeks as well as tiny sulfur ones in many Western watersheds. Then there's the little Red Quill on small streams in Wisconsin. Yet, all are the same species.
Female Ephemerella excrucians (Pale Morning Dun) Mayfly Dun
View 3 PicturesSize: 10mm. At emergence the specimen was a fairly bright olive green and there was obvious difference in color between the forewing (med. dun) and the hind-wing (pale cream). It was really noticeable as they floated by. You can just make these features out in the second photo, but not so much in the first that was taken 24 hours after capture. Total time from emergence to molting - approx. 48 hours.
Edit 2/25/13 - This specimen was originally posted to E. d. infrequens because of its size. It turns out large size doesn't hold up as a way to tell these two apart. This is because excrucians has much greater variability than previously understood. The assumption by anglers that excrucians is always the smaller of the two is apparently not supported by science. There is a lot left to sort out with western Ephemerella species. This may include new discoveries and/or synonyms (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) as well as reportage on new intraspecific variations broadening the descriptions of recognized species. Based on this specimen's Fall maturity, the best guess is that it is an unusual form of excrucians.
As to color, both species duns (nymphs too) demonstrate a tremendous amount of intraspecific variability from pale yellow to bright green with a multitude of sulfur shadings in between, ranging from pale amber, through orange to cinnamon and even dark brown. I've seen wings from pale cream through tannish and almost every shade of dun except the dark shades. Some have pigment stained leading edges matching their bodies, some don't. Most of these variations are undocumented except in angler references and periodicals. It seems a rare year that a new variation doesn't pop up to the notice of anglers.
Bottom line - size is only reliable if the specimens are smaller than size 16, pointing to excrucians. Otherwise, the only fairly dependable way to tell them apart (especially the females) is by timing as infrequens is the first of the two to appear, rarely lasting longer than a couple of weeks or later than the end of June most years. The problem with using timing for determination is it requires knowledge of the hatch sequences as they actually occurred for a given year on a given piece of water. Obviously, this kind of information is seldom available. Without it, determining between the two duns if they are larger than size 18 is speculative at best - at least until very late in the Summer.