March Brown

Other Common Names: Western March brown
Scientific Names: Rhithrogena morrisoni, R. hageni

On many rivers, the March browns are the first large mayflies of the new year. After a winter of tiny blue-winged olives and even tinier midges--always fussy and unpredictable hatches--the March browns are the heralds of all the delights of the next eight months.

In Oregon's Willamette Valley they usually start about the first week of March, although they can be earlier or later depending on the warmth of the weather. On the Willamette, McKenzie, and other Oregon rivers, March browns are beloved by local anglers even though the bugs often hatch in godawful weather. Many ardent fly fishers will spend a March afternoon shivering in a driftboat as droplets of cold rain run down the sleeve of their casting arm. If you listen close, you can hear them mummering, "It just doesn't get any better than this."

Members of the clinger group of mayflies (family Heptageniidae), March brown nymphs live in riffles and fast, rocky runs. Nymphs are so well adapted to their habitat that they are seldom found in the drift until emergence time. As the nymphs near maturity, they migrate to slower (but not slow) water, usually within a hundred yards above or below a riffle.

Hatches usually start in the early afternoon. Just prior to the hatch, nymphs are often found drifting in the current, so it makes sense to present a nymph pattern near the bottom beginning a couple of hours before the hatch. As the nymphs hatch, they often drift a long distance before reaching the surface, so you find drifting nymphs anywhere from just below a riffle to runs that are well below them.

Duns usually emerge on the surface. As trout switch their focus to the duns and you see surface rises, change to a dry fly. Sometimes, however, emergence happens underwater and the dun floats to the surface. In this case a Soft Hackle or downwing wet fly works best.

Spinners return to lay eggs over the riffles, but they usually do so sporadically and rarely in a concentration that captures the interest of trout.

 

How to Match a March brown

Hatches are matched from Westfly's database of "standard" fly patterns.

Nymph
Size 10-14 Hares Ear, Pheasant Tail. Brown
Near riffles, flats: indicator, tight line, rising nymph
Emerger
Size 10-14 Soft Hackle. Tan to red-brown body, brown wing
Near riffles, flats: surface swing
Emerger
Size 10-14 Quigley Cripple, Film Critic, Hackle Stacker. Tan to red-brown body, brown wing
Near riffles, flats: standard dry fly
Dun
Size 10-14 Sparkle Dun, Hairwing Dun, Comparadun. Tan to red-brown body, brown wing
Near riffles, flats: standard dry fly

 

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Characteristics

NYMPH COLOR: Dark brown, sometimes olive-brown

DUN SIZE: 8-15 mm (5/16 to 5/8 in)

DUN COLOR: Wings--mottled brown and tan. Body--brown on top, tan below.

OTHER CHARACTERISTICS: Nymph--gills overlap under the abdomen; flattened appearance; three-tailed; head is wider than the abdomen. Dun--two tails.