In the East they are known as Little Sulphurs, and across the West they are called Pale Morning Duns, but no matter what you label them, these closely related mayflies have the same life cycles, and require similar flies and strategies. Photo by Jay Nichols.
August 07, 2019
By Paul Weamer
When my wife and I moved to Paradise Valley five years ago to fulfill a dream of living in Montana, the Yellowstone River was a huge influencer, but there are spring creeks here too—DePuy, Armstrong, Nelson’s—and fishing them often reminds me of my formative days in Pennsylvania, especially during the small yellowish mayfly hatches that Western anglers call Pale Morning Duns (PMDs). Many Western spring creek aficionados place PMDs at the apex of summer mayfly hatches, the same way Eastern anglers envision another small yellowish mayfly, the Little Sulphur, as their summit.
There are good reasons these mayflies are important to both sets of fly fishers: They are closely related, and their appearance is one of the great events of spring and early summer.
Same but Different PMDs and Little Sulphurs are collectively grouped as a subspecies, and that’s why their taxonomic names are so similar: Ephemerella dorothea infrequens (PMD) and Ephemerella dorothea dorothea (Little Sulphur). Anglers with even a rudimentary understanding of aquatic entomology quickly notice that these two mayflies have unusual taxonomy because they are classified with three names instead of the standard two designated for most other mayflies.
These three names are called a trinomial and they denote a special relationship between PMDs and Little Sulphurs. In The Bug Book (Stackpole 2017), I describe this close relationship as “mayfly siblings” rather than the cousin-like relationship shared among all other mayflies in the Ephemerella genus. But I guess in colloquial language you could describe these two mayflies as “kissing cousins.” Though this trinomial taxonomy is unusual for most mayflies, it’s not that uncommon in our scientific understanding of other animals.
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White-tailed deer are a good example. There are currently at least 16 white-tailed subspecies in North America. I say currently because, just like mayflies, the science is always changing as new relationships are identified. White-tailed deer taxonomic names also include a trinomial, each one beginning with the genus and species Odocoileus virginianus; the subspecies Odocoileus virginianus texanus is common in Texas, and you’ll find Odocoileus virginianus virginianus in Pennsylvania. But most people would just call them all whitetails because they look and behave similarly. And it’s the same with Little Sulphurs and PMDs.
Because of this similarity, once you know how to identify and imitate PMD hatches in Western spring creeks, you can also tackle Little Sulphurs in Eastern spring creeks, and vice versa. But these important mayflies aren’t only found in spring creeks. Little Sulphurs or PMDs live just about everywhere there are trout, including freestone rivers and tailwaters.
Little Sulphurs and PMDs are so visually similar it’s nearly impossible for amateur entomologists to tell them apart. The yellowish duns exhibit wide varations in color from one watershed to the next, and some may have an olive, orange, or even pinkish hue in the thorax area. Males (left) have large red eyes that look like cherry tomatoes. (Paul Weamer photos) I’ve found no significant difference between Western spring creeks and Eastern spring creeks. They both ooze from caverns beneath the ground, rather than being formed by snowmelt or rainfall like freestone streams. Spring creeks also maintain more stable water temperatures, and they are less prone to runoff flooding. Perhaps the biggest difference between the spring creeks in Pennsylvania and the ones in Montana’s Paradise Valley are that you have to pay to fish the privately owned Montana spring creeks, while most of the Pennsylvania streams are public.
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But even the cost of fishing the Montana spring creeks gives a glimpse of the importance of PMD hatches: The fees in Paradise Valley are on a scale from $40 to $120 per rod, depending upon the time of year. And the highest fees occur during the PMD hatch, from mid-June through the end of July. Little Sulphur hatches begin earlier in the year on Eastern spring creeks, usually from mid to late May, and they generally extend until sometime in June.
Nymphs and Sunken Emergers Little Sulphurs and PMD nymphs are classified as crawlers, and they don’t swim very well. In general, PMDs can get a little larger (size 14 to 18) than Little Sulphurs (16 to 20). Both nymphs live along streambed cobbles, and in vegetation growing on the spring creek’s fertile mud bottom. These weeds are important for providing cover and safety to fish and aquatic insects, but they make it difficult to fish sunken flies, which are seemingly always getting snagged. However, there are a few ways to approach fishing subsurface flies for PMDs and Little Sulphurs before and during the hatch.
First, you can simply fish parts of the creek without weeds. Chutes and riffles often scour weeds from the stream bottom in some areas, but unless they contain large rocks to provide breaks from the current, it’s doubtful you’ll find many trout in these spots. Less turbulent adjacent areas—where calm water meets the heavy currents—are good places to find fish outside the weeds.
Some anglers attempt to nymph between the weed beds, and this is sometimes possible, but you generally have to wade very close to the weeds to make sure your flies are properly placed on the other side, and they are able to float drag-free for as long as possible. I have found that in most spring creeks you can wade much closer to the fish than you might realize as long as you do it slowly and quietly, and without sending fish-terrifying wakes as you proceed.
Spring creeks are popular places to find humans and animals, and trout get accustomed to having other creatures nearby, whether they are cows, deer, ranchers, or people with fly rods. I’ve watched Montana trout rise beside the banks while birds plucked mayflies from the surface a few inches from them. And I’ve seen trout taking mayfly duns in Pennsylvania’s Spring Creek so close to me that I could have netted them. But this isn’t necessarily true everywhere. If you’re lucky enough to have access to a private or seldom-fished spring creek, then you may need to take a more cautious approach and cast a little farther.
Fishing over and between weed beds often involves high-stick nymphing techniques with a long rod. I prefer a 10-foot rod to reach over one weed bed into the space between it and the next one. Use a short length of fly line to gently lead the flies. The leader should be near a 90-degree angle from the rod tip, and you should feel your way through the water column, using the rod tip to detect strikes.
I almost always nymph with two dissimilar flies, or at least with similar patterns of differing weights. This is an instance where a tungsten beadhead pattern in tandem with a non-bead version can be used to get both flies deep, quickly, and into the narrow slots between weeds.
If you have to (or choose to) fish from farther away, your best nymphing prospect is probably a tandem rig with a dry fly like a Parachute Adams to help suspend your nymph just above the weed beds. The length of the dropper beneath your dry should be determined by how much water is between the surface and the top of the weeds. You want your flies as close to the weeds as possible without getting snagged. I often use droppers that are approximately 10 to 12 inches long. Unweighted or lightly weighted nymphs are best for this setup. Once wet, they’ll sink just enough to where the trout can see them, but not so much to get constantly tangled in the weeds. If you’re still getting caught, trim the length of your dropper.
My nymph pattern selection for both PMDs and Little Sulphurs is pretty simple. Both nymphs turn shades of dark rusty brown before they emerge into duns. This is the exact color of a Pheasant-tail Nymph. Another one of my favorites is Joe Humphreys’s Sulphur Nymph. The fly looks a little too bright when it’s dry, but quickly darkens to a fish-fooling shade when wet.
When fish are "bulging" they appear to be rising to may fly duns, but are actually taking emergers wiggling just below the surface. In these situations, dead-drift an unweighted Pheasant-tail Nymph or Splitback Emerger. (Jay Nichols photo) Both PMD and Little Sulphur nymphs float, and weakly swim, toward the surface to emerge in the film. This is their most vulnerable stage as they wiggle to free themselves from their nymphal shuck, and trout key on them. Often, anglers notice trout bulging in the surface, and they believe the fish are eating duns.
But it’s vital to stop fishing and briefly watch what’s actually happening. If you see duns floating on the surface, are the fish really taking them? Are trout noses protruding from the surface to eat those duns? Or are the fish focusing on the wiggling emergers just beneath the surface, creating bulges with their backs or the tops of their heads? Close observation tells you if you need to fish an emerger or a dry fly.
If you see what looks like an emerger rise, an unweighted Flashback Pheasant-tail Nymph or Splitback Emerger drifting just below the surface works well. The Splitback Emerger is tied with or without a glass bead, depending upon how deep you want it to sink. It’s designed to give the impression of the yellow dun just splitting through its wing case. With these emergers drifting just below the surface, it’s often best to fish them in tandem with a Little Sulphur/PMD dry fly as a visual aid.
Emergers, Duns, & Spinners It’s critical to observe how the fish change behavior as the hatch progresses from active nymphs to emergers, and eventually to surface-riding duns. When they decide to feed on duns, trout often move from their holding lies deep in the weeds, or from undercut banks, to take up surface feeding positions. They also tend to move into tails of pools or the areas where riffles begin to smooth into glides. Fish that were previously hiding under floating weeds and in submerged woodpiles leisurely move just outside their protective lairs to reach those duns. When they change their feeding positions, that’s often your cue to change flies.
The tall, overhanging grass and other vegetation that commonly grow along spring creeks can make it difficult to present your fly drag-free to fish rising tight against the banks or other structure. In this situation, it’s again time to to move closer to the fish. I try to take one slow, cautious, sliding step toward a trout each time it rises. Patience is key.
Sometimes you’ll need to shorten your leader to make it easier to cast beneath overhanging tree branches and other obstructions. Long casts with long leaders are useful tools for dry-fly fishing, and I use them often, but they can be a hindrance if your casts are constantly snagging tree limbs. It’s better to make a good, but brief, drag-free presentation with a short leader than to struggle trying to make a longer one with a long leader. My standard tippet for Little Sulphur/PMD hatches is 6X, and I almost never use anything lighter.
Dry fly and emerger pattern options for Little Sulphurs/PMDs are legion. But I have a few favorites that work most of the time. A simple Parachute dry fly in the right size and color—tied with or without a trailing shuck—works very well. I’m also a big fan of Compara-duns and Sparkle Duns with deer-hair or CDC wings. CDC emerger patterns, tied on fine-wire scud hooks to imitate duns that haven’t quite freed themselves from their nymphal shucks, are another must-have.
There are a lot of shade variations when it comes to Little Sulphur and PMD duns. Hatch-matching legend Charlie Meck told me that he found more color variations with Sulphurs than any other mayfly species. Because of these inherent variations, I don’t believe that exact color imitation is vital for catching fish. I’ve used olive-tinted PMD patterns to fool Eastern spring creek trout, and pale orange Sulphur patterns in Montana’s spring creeks. The trout don’t seem to know the difference.
Little Sulphurs and PMDs are important early summer hatches on Eastern spring creeks like the Little Juniata (left) and also in Paradise Valley. But they are equally significant on larger trout streams like the Henry’s Fork, Missouri, and the Madison (right). (Jay Nichols photos) The final phase of the PMD/Little Sulphur hatch is the spinner fall. Most often, PMD emergences begin in late morning to early afternoon, while Little Sulphurs are an evening event. Air temperature is an important factor in determining when the female spinners lay their eggs and fall spent to the water. If it’s especially warm, they may fall at night or early in the morning. If it’s a cloudy or rainy day, you could see them in the afternoon.
Once again, the most important thing you can do to take advantage of the spinner fall is to be more observant. I’ve wasted a lot of time casting dun patterns to rising fish that wouldn’t take them, only to pause, look at the surface, and notice Little Sulphur or PMD spinners mixed with the duns. Trout often prefer these spent flies, forsaking the upright-winged duns and becoming super focused on spent spinner patterns.
Because Little Sulphurs and PMDs are long-lasting hatches often occurring for three weeks or more, trout can become acclimated to seeing the same dry flies day after day. They become picky about the ones they’ll eat. A downwing spinner imitation often inspires a take, even when the fish are obviously eating duns.
My final trick for catching difficult spring creek trout that have been eating these small, yellowish mayflies for weeks is to throw something completely different. As the Little Sulphur/ PMD hatch begins to wane, it’s time to officially declare the start of terrestrial season. Terrestrials are a vital food source for trout, and I’ve caught quite a few spring creek trout using floating ant or beetle imitations, while the fish were obviously eating Little Sulphurs or PMDs.
East vs. West If you’re a Western angler seeing your first Coffin Fly spinner fall in New York’s Beaverkill, you may not be accustomed to arriving streamside just before dark, and changing flies with a headlamp as you cast in the moonlight toward the sound of gulping trout. If you’re an Easterner making your first trip to the great trout waters of the West, you may feel a little out of your element casting oversize foam hoppers from a drift boat. But if you find yourself in a spring creek with yellowish PMDs or Little Sulphurs hatching, you can approach both with confidence. You’ve probably done this before.
Paul Weamer is the author of Fly-fishing Guide to the Upper Delaware River (Stackpole Books, 2011) and The Bug Book: A Fly Fisher’s Guide to Trout Stream Insects (Headwater Books, 2016). He is the owner/operator of Weamer Fly Fishing LLC and lives in Livingston, Montana, with his wife Ruthann and his English mastiff Olive.
