Western March Brown Mayfly
The Western March Browns are species of the Rithrogena genus of the
Heptageniidae family of mayflies. They are among the first mayflies to hatch in
many western trout streams. The hatches depend greatly on the unpredictable
weather of the early season, but usually are fairly heavy and condensed into a
short period of time.  The “Western March Browns” inhibit the fast waters of riffles
and runs of the streams but are occasionally found in the slower to moderately
moving water.
The
morrisoni species is the first to hatch, and may be followed by the hageni
within a few weeks. The
morrisoni hatch can occur when some of the streams are
blown out from the runoff. The morrisoni is usually found in moderate to fast
moving water, but slower than the
hageni that prefers fast streams. The futilis
and undulata species usually hatch in the summer months and as late as early
Fall. These hatches are usually not very prolific and may be short and scattered.
The duns hatch off and on for a few hours and are rarely concentrated but the
spinner fall may be compacted into a shorter time and dense. It is usually the
best stage to fish. Both of these species can be found in moderate to slower
moving water than the other two species are usually found in.  

We have only found a very few occasions that we have been able to fish the
Western March Brown early season hatch. Most of those occasions occurred
during the spinner fall of those species that hatched in the summer and early fall.
We do not want to over state the importance of this hatch. We have only been
able to catch a few fish as a result of it. This may have been a product of just not
being at the right place at the right time. Part of the reason is that we rarely fish
the early season in the West. If you do, you want to have imitations of all stages
of this mayfly for the early season as well as the late season hatches.
Copyright 2014 James Marsh
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"Perfect Fly" Western March Brown Dun