Pale Morning Duns: Color Me Yellow, or What?
Okay, so the salmonflies and golden stones are almost done for the year. Don’t despair and think good dry fly fishing is over. In fact over the next month and a half some great hatches will be happening, hatches that produce as good or better surface activity as the big stoneflies. One of these hatches is the mayfly somewhat misleadingly called the pale morning duns or PMDs. I say misleading because they aren’t always pale and they don’t always show up in the morning. I guess that just proves you can never trust a common name.
Pale morning duns rank right up their with blue-winged olives in terms of characteristics that produce great fishing. They are abundant, widespread in all types of rivers from small spring creeks to big tailwater rivers, emerge slowly enticing trout to feed on them (more on that in a bit), and their hatches are fairly consistent for three to six weeks, which means if you miss them one day you should find them still hatching the next.
PMD nymphs are known as crawlers, and belong to the important family Ephemerellidae and genus Ephemerella. There’s been a bit of debate about just what species lives in western streams and taxonomists recently changed the species name from Ephemerella inermis to Ephemerella excrucians. This means nothing to the trout, or the flies you use to match them, so you can now forget it ever happened!
Though known as crawlers PMD nymphs swim surprisingly well, almost as well as the speedy little blue-winged olive nymphs. Thus, while they may crawl along the bottom they also move around and regularly get into stream drift where they are seen by trout. Nymphs prefer moderate to slow currents and find a wide range of substrate to their liking, with small to moderate gravel/cobble mix, to small gravel and sand, to beds of aquatic plants and moss all acceptable. This is one reason why PMDs are found in so many different types and sizes of streams. Because of PMD nymph abundance, widespread presence, and frequency in stream drift, I have found fishing nymph patterns that match them one of my most consistently successful patterns for nymph fishing. Ever wonder why a size 16 or 14 hare’s ear nymph works so well?
PMD hatches start right now, i.e. early June, and last well into the middle of July. That’s a long time, and it should give you plenty of opportunity to get on a stream while their hatches are coming off. The time of day you’ll find them emerging can be a bit unpredictable, however. If they hatch in the morning it will usually be late morning, say around 11 o’clock. But it is just as likely that their hatches won’t start until one in the afternoon or even later. Weather is the big driver of daily hatch timing. Hot weather will drive the hatches to late morning, while cooler weather will push it into the afternoon. Also cloudy overcast conditions generally create a daily hatch that lasts much longer - say two or three hours long - than you’ll find on a bright sunny day when the hatch will last just an hour or two at most. As a result it’s much easier to miss the hatch on a bright day, by not being in the right place at the right time. As they say, “timing is everything!”
One of the confusing yet most important aspects of success during a PMD hatch is understanding how they emerge. Most mayflies emerge from nymph to dun in the surface film. The nymph swims to the surface, its shuck splits open, and the dun wiggles free and pops up on top of the water. Some PMD nymphs do the same thing, but many don’t. Instead the dun actually escapes from the nymphal shuck underwater, often while the nymph is still clinging to the bottom. Therefore, the dun must rise up through the water column and break through the surface film, then dry its wings before flying away. Such behavior makes the duns sitting ducks to feeding trout, both underwater and on the surface. For the angler this means that when your dry flies fail, instead of cursing the trout God’s, put on a small subsurface pattern like a soft hackle that will match the dun rising up to the surface. It also means that cripples - duns that struggle and die in the surface - are quite common during PMD hatches. Sometimes it is much more effective to fish imitations of these crippled duns than that of a nice looking healthy dun with its wings held upright. Fish both emerger and cripple patterns dead drift just like a dry fly, but fish them just below the surface to as deep as a foot or two depending on how the fish are feeding. Understanding this aspect of PMD behavior can save you many hours of frustration during their hatches.
Also, don’t forget about PMD spinners. Those duns that make it off the water, fly to shoreline vegetation where they molt into spinners within about 12 hours. The spinners then form mating swarms over the water and the females lay their eggs by falling on to the stream’s surface. Once their eggs are laid they die on the surface with their wings flat out on the water making them very had to see. Always look for the easier to see mating swarms above the water. Then if you see little subtle rises fifteen or twenty minutes later, you will usually be dealing with trout taking spinners. PMD spinner falls can be in the morning, as early as 8 or 9 AM, or in the late afternoon/evening. This is again driven mostly by weather conditions, and can change day to day. Observation is the key.
One of the characteristics of PMDs that can be particularly maddening and confusing to fly fishers is color. That is, what color best matches the nymphs, duns, and spinners? Fly fishers, and especially fly tiers, spend a lot of time trying to match just the right color of the natural. But when you go into a fly shop there will be bins of PMD or other fly patterns of different colors. What gives? Well, if there’s one thing I’ve found from collecting aquatic insects for over forty years is that color is not a definite thing, even between individuals of the same species from the same stream, and PMDs seem to exhibit this color variability more than most. The photos of nymphs and duns shown here, where collected from the same stream, and even the same rock, yet you can see significant color differences. I have seen similar color differences for many other species. This shouldn’t be that surprising, since what other animals of the same species all come in the same color? Color variation between individuals is the norm not the exception, and that is true for insects as well.
So, what does this mean? To me it means that I don’t have to be so worried about color when selecting my fly pattern. I pay attention to color, but if my fly doesn’t seem just right, no big deal. I believe matching the size correctly is much more critical than matching color correctly, yet most angler’s pay way more attention to color than size. The bottom line is that over the next month or more you will want some nymph, emerger, dun, and spinner patterns for PMDs in your fly box ready to go. Sizes generally range from 18’s to 16’s, but check the local hatch carefully to get it right. Also look at the color of a half dozen or more naturals side by side and get a feel for just how variable it might be. Then make sure you to get a good presentation of you fly over the fish. When everything is right you’ll know it - the trout never lie!