Marching Orders: Unlocking the Secrets of Eastern March Browns

Eastern March Browns are found predominately from the Eastern United States to the Upper Midwest. Western March Browns (Rhithrogena morrisoni), which populate rivers and streams from the Pacific Coast to the Rocky Mountains, belong to an unrelated, though similar-appearing mayfly species.

Eastern March Browns constitute an important mayfly hatch on most of the East's best trout waters. Anglers who fish the Elk River in West Virginia, or Elk Creek in central Pennsylvania, are all familiar with this species. I've been fortunate to live and fish along several of the famous streams of New York's Catskill Mountains. And the March Brown hatches along the Neversink, Willowemoc, Beaverkill, and the branches of the upper Delaware River are all worth scheduling time to fish. Central Pennsylvania's Big Fishing Creek and my current home stream, Penns Creek, also have excellent populations of March Browns.

Water temperature near the mid-50s is necessary for triggering March Brown emergences. But because these mayflies occupy such a vast region, emergence dates often vary widely from one stream to the next. March Browns appear in the mountain freestone streams of western North Carolina nearly a month before those in the Ausable River in New York's Adirondack Mountains, or Connecticut's Housatonic River.

The Internet is your best source for finding information about March Brown hatches and the rivers and streams that have them, and fly shops and guide services are useful contacts for timing the hatch. Local weather patterns heavily influence all mayfly emergences, so it's best to contact people who are on the stream every day for the timeliest information.

Living in the East, I've witnessed phenomenal mayfly hatches. Many of them have faded into the murkiness of memory, and I'm sure that many more have been entirely forgotten. But the hatch I best remember occurred on the Beaverkill's most heavily fished water, Cairns Pool.

It was a rare spring day that provided a break from managing the fly shop and I desperately wanted to find mayflies and rising trout. But the weather was not cooperating. Melting snow and heavy spring rains had swollen the local rivers to near flood stage. So I was out for a drive, hoping that just being near the water would mitigate the longing for trout fishing that a hard Catskill winter fosters in its residents.

I steered my car into the pull-off at the head of Cairns Pool, and as I stepped out for a look, I saw large mayflies struggling in the heavy currents, flopping and falling as they attempted to escape the roiling water. Potentially drowning in the swollen river wasn't the emerging March Brown duns' only concern; several acrobatic brown trout were forcefully slashing through the currents, ravenously grabbing flies before the water swept them beyond reach.

Though the high water kept me from fishing, I'll never forget how enthusiastically the trout pursued those March Browns.

Misinformation

March Brown emergence is one of the East's best hatches, yet a great deal of misinformation and controversy surrounds it. Angling writers often include the Eastern March Brown on their lists of "super hatches."

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This lofty status could give some anglers the impression that March Browns appear in the same water-blanketing numbers as some other spring mayflies. They do not. March Browns usually emerge in a trickle through the day, often beginning in late morning and continuing through the afternoon. Once trout notice the hatch, they become keenly aware and pursue this mayfly through all its lifecycle stages.

This amplified trout awareness, combined with a relatively sporadic hatch, creates perfect conditions for blind-casting drys to likely trout holding spots. In fact, blind casting drys and emergers is often the most productive technique during, and for a brief time after, a March Brown emergence.

Although finding trout rhythmically feeding on March Brown duns is rare, it does happen. I had a wonderful, rainy afternoon this past spring when the fish actively fed on March Brown duns. But you should never expect that kind of trout activity with this hatch. Be prepared to blind-cast your flies, or wait for the mythical March Brown spinner fall.

The hype surrounding its super hatch status isn't the only misleading March Brown information. Even the common name, "March" Brown, is a misnomer, considering they usually hatch in May.

So how did they get their name? Fly-fishing experiences in Europe helped pioneering American fly fishers understand the new insects and trout they encountered in North America. Eastern March Browns (Maccaffertium vicarium) closely resemble the European species Rhitrogena germanica. These brownish European mayflies hatch in March, so anglers there gave them the common name March Browns. When anglers in the New World encountered the similar-looking M. vicarium, they adopted the same name.

But as American entomologists expanded their studies at home, new ideas and opinions were formed. For many years, March Brown taxonomy was Stenonema vicarium. Another mayfly, commonly called Grey Fox by anglers, was listed as a separate species, Stenonema fuscum. Today, science tells us that March Browns and Grey Foxes are actually minor variations of the same species commonly separated by size. And the mayfly once known as the Grey Fox (S. fuscum) has now been reclassified out of existence.

The former March Brown genus, Stenonema, has also been replaced by Maccaffertium, named after Purdue University's professor of aquatic entomology, Patrick McCafferty. McCafferty recently sent me an e-mail stating, "M. vicarium has been a major source of taxonomic confusion because of the range of variability in both nymph and adults." So if professional entomologists have struggled with the differences and similarities between March Browns and Grey Foxes, it's not surprising that fly fishers are also confused.

Prominent Penn State University entomologist Greg Hoover has his own strong opinions on the Grey Fox/March Brown debate. Hoover says that many of the mayflies anglers call Grey Foxes aren't really March Browns (M. vicarium) at all, but rather Maccaffertium ithaca, or Light Cahills.

The March Brown/Grey Fox debate, though important, is largely a scientific exercise. Some amateur angler-entomologists still argue that the two species should be separated. But professional entomologists' classifications stick. Nonetheless, there are angler-important differences between mid-May March Brown hatches and emergences of the smaller, March Brown-looking mayflies that hatch from late May through mid-July.

Early and Late

By the time the March Browns arrive, anglers have already been fishing hatches of small- to medium-size mayflies such as Hendricksons and Blue-winged Olives for up to two months. But the first March Browns of the year are huge in comparison. March Browns in fertile waters can easily fill #8, 2X-long hooks and the small ones are #10.

Early March Browns begin hatching in mid-May when the water is often still cold, and they appear during the warmest part of the day, usually from late morning through the afternoon. These mayflies continue hatching through the end of May and often overlap with big Sulphurs (Ephemerella invaria), the beginning of the Green Drakes (E. guttulata), and the insects fly fishers call Grey Foxes.

Grey Foxes begin hatching near the end of May and can continue sporadically until mid-July. The flies–nearly identical to their earlier arriving brethren look like shrunken, sun-bleached, #12-14 versions of the larger mid-May flies. The name Grey Fox implies that the flies are gray, and many tiers use light gray materials for the wings or body. But I've never encountered a Grey Fox that actually looked gray. Most of them range from pale tan to cream, with light brown markings on their legs and backs. Grey Foxes usually emerge in the coolness of the evening because the water has warmed, similar to emergences of the various Cahill species. Grey Fox hatches often overlap with Slate Drakes (Isonychia bicolor), little Sulphurs (E. dorothea dorothea), big Blue-winged Olives (Drunella cornuta), and Light and Cream Cahills (Stenonema interpunctatum interpunctatum and M. modestum) during their long emergence period. [Aquatic insect body coloration can vary greatly from stream to stream, so the color descriptions given here for the nymphs, duns, and spinners are basic guidelines. Examine March Browns from your own waters to find the colors that most appropriately match the hatch. The Editor.] 

Eastern March Brown Nymphs

March Brown nymphs are in the family of clingers. They are usually found holding on to the bottoms of rocks in riffles and swift-moving glides. Nymphs have three tails and reddish-brown to dark, blackish-brown bodies, with darkly ribbed amber abdomens. Their wingpads and legs are also dark brown, but lighter-colored mottling on the legs is prominent.

March Brown nymphs have wide, flat bodies. Use a flattened tungsten or lead wire underbody to make your nymphs appear like the naturals. March Brown nymphs migrate from fast water to slack areas around boulders and near the shore, or even slow pools, to emerge during high-water conditions. But if the stream flow is low, it's common to find them emerging in riffles.

You don't need to wait until you see the first March Browns hatch to fish the nymphs. Trout start feeding on them in early May about a week or so before the hatch commences, when the bugs begin migrating to emergence areas.

Dead-drifting #8-10 nymphs in the riffles is productive, but slowly stripping the flies toward shore, like a streamer, can be better, particularly if the water is high.

I've also caught a lot of trout with March Brown wets [see recipe]. Fish these flies with a traditional down-and-across swing, or dead-drifted on a leader weighted with split-shot. From late May through mid-July, fish smaller nymphs and wets (#12-14) to imitate Grey Foxes.

Emergers and Duns

The early March Brown duns are strikingly beautiful. The color of their thoraxes and abdomens ranges from creamy tan to pale yellow, significantly lighter than the bold, dark brown markings on their backs and legs. Many March Brown dry-fly patterns are tied with bodies too dark to properly match the naturals.

The fly's belly is most obvious to a rising trout, so it's important to properly imitate the belly color.

March Brown wings are usually tannish-yellow and heavily mottled with dark brown to black venations. The wings are swept back toward the tail in a somewhat exaggerated position compared to other mayflies.

March Brown duns have two tails ranging in color from amber to dark brown. Legs are cream, with areas of dark brown banding on the femurs. March Browns have slightly wider abdomens and thoraxes than most mayflies, and their legs extend out from their bodies, creating a wider, beefier stance. 

Duns emerge in, or just beneath, the surface film, making Antron or Z-Lon trailing shucks effective additions to your emerger and dry-fly patterns. Because the flies are large and highly visible, fish subtler, flush-floating drys like parachutes, Sparkle Duns, and Truform flies for trout rising in slow pools. The flush-floating, yet easy-to-spot, deer-hair emerger is also one of my favorites for this hatch.

March Browns often flap their wings and move on the surface while attempting to fly. So if your dead-drifted drys aren't producing, try skittering or twitching a standard Catskill-style pattern in front of the fish.

Blind casting drys during the March Brown emergence works particularly well during low or average flows. The lower water places the insects closer to the trout, and the fish eat them readily. I prefer standard Catskill-style March Browns and Ginger Quill Variants when I blind-cast, because they float well and they're highly visible.

Spinner Theory

March Brown spinners have two dark brown tails banded with lighter areas. Their bodies are reddish-tan and ribbed dark brown. Their wings are clear with brown venations and an area of brownish edging along the front (closest to the head). Legs are amber, with dark brown banding along the femurs.

Male March brown spinners have unusually large eyes that can be powdery shades of blue, cream, or light gray. Imitating the spinners is not difficult. Just about any big (#8-10, 2X-long) Rusty Spinner in your fly box will probably work. The problem is actually being streamside when the bugs hit the water.

Timing an Eastern March Brown spinner fall is one of fly fishing's greatest quests, sort of like searching for the mayfly Holy Grail. Almost every hatch-matching angler has seen spinners, passing overhead in waves, dropping occasionally to eye level, teasing their fall. But then darkness hits. And as you stand there in the twilight, sure that the fall is imminent, the bugs just disappear, returning to the streamside foliage to wait another evening. Why?

Mayflies have few opportunities to make choices during their short lives. When the water reaches a specific temperature for a specific period of time, their bodies begin changing, and they must emerge.

But once they become sexually mature adults, or spinners, their options increase. If air temperature is too cold or a gusting wind or inclement weather suddenly appears, the bugs can choose to complete the cycle another day.

Though it's easy to blame the weather any evening the March Brown spinners do not reach the water, there could be other reasons.

I was watching a March Brown spinner flight in front of my home on Penns Creek last year when I noticed something strange. As darkness approached, and it become obvious that the spinner fall wouldn't happen that night, a few of the bugs began mating and falling spent to the water. I stayed streamside for a long time after, but the bulk of the spinners did not fall. But if air temperature, humidity level, or some other weather ingredient was the determining factor, why did a few flies complete their cycle when hundreds of others did not?

Another reason for the often unreliable March Brown spinner fall is perhaps an inequity in the male-to-female ratio. This may be caused by the peculiar manner by which March Browns emerge. Most mayfly emergences begin slowly with only a few insects, then quickly build, producing large numbers of flies until they peak and then diminish to a few final remaining stragglers.

When these populations emerge simultaneously, it creates an even distribution of males to females. Not the case with March Browns.

March Brown hatches produce relatively smaller numbers of insects daily. March Browns can live for extended periods once they become spinners most mayflies can. That's why it's common to see thousands of spinners at night, when the bugs seem to emerge in much smaller numbers during the day. All those spinners are the result of days of accumulation. It's common for initial emergences of many mayflies to include mostly males. So perhaps March Brown spinners have the same problem I encountered at parties when I was in high school: too many dudes and not enough girls in attendance. Slowly, as the March Brown hatch runs its course, enough females emerge to match the males in number, and mating occurs. But it often happens just as the emergence does, in a trickle.

Keep it Super

It's possible to experience a heavy March Brown spinner fall. Perhaps a change in water temperature induces all the flies to hatch simultaneously in a shortened window. Or perhaps it occurs for reasons known only to the March Browns. I've been fishing these hatches with dry flies religiously for a long time. And I can count on one hand the number of times I hit the March Brown spinner fall perfectly. You want to be streamside when this occurs. The fishing is great, every time.

Anglers visiting me at the TCO Fly Shop in State College often seem to be disappointed by March Browns. They expect more bugs or more rising fish. But if you understand the hatch and how to fish it, you can find some of the most exciting angling opportunities of the year. For me, March Browns are a super hatch because trout love them. And I anxiously await their return with the advent of each new fishing season.

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Paul Weamer is Fly Fisherman's Eastern field editor. He and his wife, Ruthann, live in Coburn, Pennsylvania, on the banks of Penns Creek.