.......................  ......Fly Fishing Yellowstone National Park

07/14/09

Fly Fishing Yellowstone - Pale Morning Duns

It occurred to me that I haven't written about the most important hatch in
Yellowstone Country and that is the Pale Morning Dun. There are a few anglers
that would argue the BWOs are more important. I wouldn't want to defend either
insect as being the most important. I think I mentioned the PMDs a few times
when writing about the Firehole and Madison Rivers back in the spring but I
didn't cover the hatch.

Pale Morning Duns are species of the
Ephemerella genus. There are two
species in the park that are found in large quantities. They are the
infrequens
and the
inermis. The facts about these mayflies stand out. The hatches are very
predictable and they last a long time. The
infrequens can start hatching as soon
as the water temperature stabilizes around fifty to fifty five degrees. The
inermis
species usually hatch later or anywhere from two weeks to a month after the
infrequens start. The only reason I even mention these species of the PMDs is
just to point out they hatch at different times. You cannot tell them apart without
a microscope so their appearance isn't a factor. Many streams have both
species. Both species can continue to hatch for as long as two months and even
longer in some streams. Hatches started on the Firehole River and the Madison
around the first week of June.

These mayflies can vary some in size from stream to stream. Most of them are
closer to a hook size 18 than a 16 but they range within those sizes depending
on the stream. You guys from the East would be far ahead in learning about this
hatch if you first started considering it to be a Sulphur. They are similar in many
respects and they are in the same family of mayflies. During the next few days I
will be dealing with this little mayfly. If you plan on fishing Yellowstone anytime
soon, you certainly need to become familiar with it.






Copyright 2009 James Marsh