Hatches Made Easy:
American March Browns (Maccaffertium vicarium)
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.
Now those that question that for any reason can read on. Those that don't can
skip down to the American March Brown.
Anglers that refer to the Gray Fox are not nuts. For years entomologist list a
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
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. The colors also vary throughout the long hatch. What anglers call
the Gray Fox is really just a smaller size and slightly different color of
the American March Brown. In other words, in terms of what is important to
anglers, size and color, there is a difference. There is nothing wrong with varying
the size and color 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.
American March Brown:
The March Brown is one of the most plentiful mayflies in the Great
Smoky Mountain National Park. We have not yet found a stream that didn't
have them. They are large, beautiful mayflies that are very noticeable on the
streams. The nymphs are clingers that fare very well in the slightly acidic, fast
moving pocket water of the Smokies.
From what I said so far, you would think they would be the most important mayfly
in the park but that is far from being the case. 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 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
hatch. The March Brown hatch normally occurs from about the middle of April
until the middle of June. It is not a bi-brooded mayfly. It is a single hatch with a
very long duration. The "multiple" hatches lessen the importance of the March
Brown. In the forthcoming articles we will cover the details of the hatch.
Coming Up Next:
American March Brown Nymphs
Copyright 2008 James Marsh