The infrequens species may start emerging as soon as the water temperature gets into the low fifty degrees Fahrenheit
level. This species can hatch for as long as a couple of months on the same river. The inermis species start emerging
later on in the year, usually early summer, depending on the stream. It can last as long as two months on the same
stream. There are a couple of other species that are not that prevalent. These two important species, the inermis and
the infrequens, are so similar that they cannot be distinguished without the aid of a microscope. As far as I know, trout do
not have microscopes and therefore, we have only one imitation for each stage of life of the two species.
Pale Morning Duns prefer streams with rooted vegetation, but many western streams with a stable flow of water have
consistent PMD hatches. For example, I don't know of a stream in Yellowstone National Park that doesn't have this
mayfly. It is certainly a common mayfly that you need to become familiar with and have imitations of if you plan on fishing
many western trout streams.
Pale Morning Duns are found in the slow to moderate flowing waters of the streams they inhabit. They are crawler
nymphs that live for a year. They can swim, although not very well. Like many other nymphs, their exact coloration is
somewhat a product of the stream they live in, and the color of the nymphs will vary depending upon the water. I would
think trout eat these nymphs on a regular basis since they are regularly exposed to them, or at least they don't tend to
stay underneath rocks like the clinger nymphs do. They do stay down between the cobble and gravel on the bottom of
the stream. Where there's a lots of vegetation, to some extent, they can probably avoid being eaten by hiding in the
plants. There's certainly no shortage of these nymphs, so there are always plenty of them that doesn't get eaten by the
Although the nymphs are found in slow to moderate moving water, don't overlook the fact that this can be in slower,
calmer areas of streams that consist mainly of fast, pocket water. For example, the Gallatin River in Montana, normally
referred to as a fast, pocket water trout stream, has a good population. You will find them in the slower sections of water
in pockets along the banks, and in pockets behind large rocks and boulders. They are also found at the ends of long
runs and riffles and the slower moving water on the inside of the river bends. Most streams have as many or more of
these nymphs as any mayfly nymph that inhibits the stream, so fishing an imitation of the PMD is always a good choice.
You can fish an imitation of the nymph on the bottom anytime during the season prior to the beginning of the long hatch.
That sometimes means you can fish the PMD nymph from the time the season opens until the PMD hatches have ended
on that stream. The hatches normally start mid-morning. During those days a hatch is occurring, you can start out with a
nymph imitation, and continue to fish it up until the hatch starts. The nymphs swim to the surface and hatch in the skim.
You may even want to continue to fish the nymph in the surface skim after the hatch is underway, although we have
emerger patterns that I think are much better for this stage of the hatch.
In pocket water prior to a hatch, I would fish the nymph imitation in the current seams and the through the long runs.
Weight it down and keep it on the bottom as much as possible. Use a very short, up and across cast and follow the
nymph downstream holding the rod tip high. Continue until the nymph is down and across and then make another cast a
couple of feet upstream of the previous one. You will have to approach the areas you are fishing carefully to avoid
spooking the trout when you are making this short of a cast.
In smooth water you will need to make a much longer, up and across presentation and keep the nymph on the bottom by
weighting the tippet a few inches above the fly and continuously mending the line. Smooth water can be very deceptive.
The current is usually very strong even though the water is smooth. In some cases, there is a lot of vegetation that your
fly will hang on unless you select the areas to drift your nymph through. It is also difficult to keep a drag free drift in the
swirling, smooth currents. I watch the end of my fly line to detect strikes but you may prefer to use a small strike indicator.
Fish the nymph until it is in the down and across position before making another cast.
Pale Morning Duns emerge, as their name implies, in the morning from 9 am to 11am as a general rule. Like many other
mayfly hatches the activity usually last only a short time, an hour or so, although it may go much longer on during cloudy,
overcast days. The PMD nymphs swim to just beneath the surface of the water and shed their nymphal casing. It is
during this time that the nymphs are suspended the trout has the best opportunity to feed on the emerging duns. PMDs
commonly have a large proportion of cripples and trout are well aware of it, feeding on them with ease.
Flies fished just under the surface of the water imitating the emerger are usually effective during a hatch. Normally PMD
nymphs migrate to hatch in calmer, slower moving water that is near their normal moderate to fast water habitat. A long
leader and tippet of 6x or even 7x will get far more results that something shorter and heavier. This type of water can
require a down stream, or cross-stream presentation that is made to an individual rising fish. Be sure to get the fly
beneath the surface film before it gets to the fish.
We don't suggest that you stick with the emerger patterns very long after the hatch begins. They are very effective flies
but you can catch plenty of trout on dun patterns, or the dry fly which most anglers prefer. Like the nymphs, the exact
color of the dun varies depending upon the location, but the differences, if any, are minor.
It is not uncommon for the fully emerged duns to float a long time on the surface before flying away. This is especially
true during the first part of the hatch when the water is still cold. We consider a long time to be a minute or two versus a
few seconds.Cripples or duns that are deformed are common with this hatch. The cripples will stay on the surface much
longer, of course.
A down-stream or cross-stream presentation will usually spook less fish although you can fish pockets of calm water with
an upstream presentation in certain waters. We fish upstream or slightly up and across anytime we can do so without
spooking fish. This is always the best way in streams with fast moving pocket water. In slower moving, slick or smooth
water, you may need to fish down and across. Keep in mind that even in streams with fast moving pocket water, the
PMDs will hatch in the calmer, smoother water such as pockets and the outside edges of fast currents.
It there are not a lot of fish rising to the emerging duns, then you may need to fish to an individual fish. This is a matter of
getting your fly to drift over the fish at the right time. In smooth, slick water, this is not exactly easy to do without spooking
the fish. The hatches generally take place earlier during the hottest days of the season. You may need to be on the
stream fishing by 9:00 o'clock in the morning which many anglers consider early, especially if they fished late the day
before. The hatch may be over by 10:30 to 11:00 am.
Look for the spinners to fall over ripples upstream from the calmer water from which they emerged. Warm, calm days are
the best for large spinner falls. Spinners fall both in the mornings and evenings. Generally, the spinner falls occur in the
mornings during warmer weather. After they mate over water, the males fall to the water and die. Later, the females
deposit their eggs by flying over the riffles and dipping slightly into the water. They then fall spent and die.
Like the duns, the colors of the spinners can vary a little from one stream to another. Spinners can be difficult to see
although the insects may cover the water. If you are not familiar with the spinner fall, it is possible to be on the water and
not even know it is happening. The trout tend to sip the spinners and although you may see the rises you may not have
a clue as to what the fish are eating. They are very difficult to see even when there are a lot of them on the water,
especially during the low light conditions they occur under. A skim net will quickly tell you if they are on the water and is
the best way to determine if the spinner fall is occurring. Look for areas where the spinners congregate in such as slow
water below riffles, seams of current and eddies.
Usually the females actually touch the water to deposit their eggs but sometimes they drop them from slightly above the
water. The trout may take them while they are depositing the eggs but they are more likely to eat them after they die and
fall spent into the water. The females die as soon as they have deposited their eggs. It is much easier for the trout to
position themselves downstream from the area they deposit their eggs to eat the spinners than it is to chase them
around the faster water where they deposit their eggs.
Use a very light tippet and make an upstream or downstream approach that best presents a drag free presentation for
the type water you are fishing. Generally, a down stream presentation is best for smooth, calmer water and an upstream
presentation is best for streams consisting mainly of pocket water. In rough water, you will want to concentrate on the
areas the spinners would congregate in such as the ends of riffles and runs and the heads of pools.
The Pale Morning Dun
Copyright 2015 James Marsh
July, 2015 Issue
he Pale Morning Dun is considered by many anglers to be the most important mayfly in the West. It certainly
rivals the Blue-winged Olive species for that title. This is primarily due to the fact that they emerge over such a
long period of time and provide fairly predictable hatches. These are species of the Ephemerella genus, often just called
PMDs. If you have only fished eastern trout streams, you may compare them with the Sulphurs, a somewhat similar mayfly.
Pale Morning Dun
Pale Morning Dun
Pale Morning Dun
Pale Morning Dun Spinner