Pale Morning Duns
.............................Fly Fishing Yellowstone National Park
04/25/08


The Pale Morning Dun is considered by many anglers to be the most important mayfly
in the West. It certainly rivals the Blue-winged Olive species for that title. This is
primarily due to the fact that they emerge over such a long period of time and provide
fairly predictable hatches. These are species of the
Ephemerella genus, often just
called PMDs.
The
infrequens species may start emerging as soon as the water temperature gets into
the low fifty degrees Fahrenheit level. Hatches can begin taking place in the Firehole
River soon after the season first opens. This species can hatch for as long as a couple
of months on the same river.
The
inermis species start emerging later on in the year, usually July depending on the
stream, and can last as long as two months on the same stream. There are a couple of
other species that are not that prevalent. These two important species, the
inermis and
the
infrequens, are so similar that they cannot be distinguished without the aid of a
microscope. As far as I know, the trout in Yellowstone do not have microscopes.
They prefer streams with rooted vegetation but any of the streams with a stable flow of
water usually have consistent PMD hatches. I don't know of a stream in Yellowstone
National Park that does not have this mayfly.
This is certainly a mayfly that you need to become familiar with and have imitations of if
you plan on fishing Yellowstone. We will be dealing with the details of fishing this hatch
the next few days.

Coming Up Next:
Pale Morning Duns - Nymphs

Copyright 2008 James