American March Brown

Lets start out making things real simple. Forget a mayfly called the Gray Fox. There is no
such thing. What anglers call the Gray Fox is the American March Brown. That said, now
consider that anglers that refer to the Gray Fox are not nuts. For years entomologist list
Stenonema fuscum species. During that same time period the scientific name for the
American March Brown was the
Stenonema vicarium. The fuscum, or Gray Fox, was
thought to be a different species. More studies proved the
fuscum was the same species
as the
vicarium. For other reasons with nothing to do with any of this, more recently, the
Stenonema vicarium was reclassified. It is now the Maccaffertium vicarium.

There was another reason for the Gray Fox name and the one that made sense. The
American March Browns hatch over such a long period of time they are available at one
time or another in various sizes depending on the time they hatched. What anglers call
the Gray Fox is really just a smaller size and a slightly different color of the American
March Brown. In other words, in terms of what is important to anglers - size, there is a
difference. There is nothing wrong with varying the size of the March Brown imitations to
match the ones on the stream at any given time.

Why is the name "American" added to the name March Brown? One reason is because
there are two March Browns - a Western March Brown and the American March Brown.
Are they similar? No, they are not similar. They don't even belong to the same genus. By
the way, this can be a factor when you are buying flies. You may purchase Western
March Brown imitations for American March Brown mayflies if you are not careful.

American March Brown:
The March Browns are large, beautiful mayflies that are very noticeable on the streams.
The nymphs are clingers that fare very well in fast moving pocket water. The March
Browns have a very long hatch period - as much as a couple of months. They hatch
sporadically and rarely in large quantities. They even hatch at various times during the
day. The hatch is usually not concentrated into a short period of time. About the only
heavy concentration of March Browns that you are likely to see is during the spinner
fall which occurs just before dark. The spinner fall occurs in a short time period and this
congregates the mayflies that have hatched.  

Another problem is that during the long hatch period, several other mayflies usually
hatch. The March Brown hatch normally does not occur in the month of March although it
may in certain locations. It is not a bi-brooded mayfly. It is a single hatch with a very long
duration. The "multiple" hatches that normally occur at the same time lessen the
importance of the March Brown. In the forthcoming articles we will cover the details of the
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American March Brown Mayfly
American March Brown Dun Mayfly