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March Brown

Scientific Names: Rhithrogena morrisoni, R. hageni

Common Names: March brown, western March brown


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NYMPH SIZE: 8-12 mm (5/16 to 1/2 in)

NYMPH COLOR: Dark brown, sometimes olive-brown

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

DUN COLOR: Wing: 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 has two tails.


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About the March Brown

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 the far west, such as 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."

In the intermountain west, March browns begin hatching in mid- to late-March in almost any weather and anglers have a more rational attitude about the insect.

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, switch 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.

Articles About March Browns

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Fishing the March Brown Hatch On many rivers, March browns are the year's first hatch of big bugs. Mike Schoby


Nymph. (photo © 2006 Arlen Thomason. Used by permission.)


Dun. (photo © 2006 Arlen Thomason. Used by permission.)


Female dun (left) and male spinner (right). (photo © 2006 Arlen Thomason. Used by permission.)

Matching March Browns

Only standard fly patterns are shown. Click here for all matching flies in the database.







Hares Ear, A. P. Black, Pheasant Tail


Indicator, Tight line, Rising nymph

Near riffles


Soft Hackle


Surface swing

Near riffles, flats

Quigley Cripple

10-14/Tan to red-brown body, brown wing

Standard dry fly

Near riffles, flats


Comparadun, Sparkle Dun, Parachute Hares Ear

10-14/Tan to red-brown body, brown wing

Standard dry fly

Near riffles, flats

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