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

New KISS Bug Series - Part 22

Pale Morning Dun

I can start out telling you what you need to know about this mayfly with a very blunt statement. It's the
most important aquatic insect in Yellowstone National Park.
In fact, it's the most important insect in
most all of the trout streams in the Western United States.

There are two species of the mayfly called a Pale Morning Dun but they both are so similar to each other
you would need a magnifying glass to tell the difference even if you knew how to do that. I know the trout
can't tell the difference, other than they certainly recognize the different times they hatch. Put simple for the
KISS series, you don't need but one imitation of each of the Pale Morning Duns' stages of life to cover both
species. That brings up another important point. Trout eat these mayflies in every stage of their life except
as an egg. They eat the nymphs, duns and spinners and they usually represent a large part of their diet..

The nymphs accent to the surface and emerge in the skim. Trout eat them like popcorn when they are
emerging. Another thing that makes the Pale Morning Duns popular with anglers is the fact that they
usually ride the currents a relatively long time before departing the water. Dry fly fishing is generally very
good when they are hatching. The hatches take place in the early part of the season when the day is the
warmest. Hatches will begin as early as the opening day of the season on the Madison River and Firehole
Rivers some years. By the first or second week of June the hatches are usually in full swing on these two
rivers. If the weather is hot, they may emerge as early as 9:00 to 10:00 AM. Trout eat the spinners just as
well as the other stages of the PMDs. Spinners can fall in the morning and evenings depending on the

The best weather for a good Pale Morning Dun hatch is a light snow or a light misting rain. They seem to
hatch for a very long period of time under these adverse conditions. Bright clear days slows the hatches
down but they are usually some that hatch in spite of the conditions. In the Northeast corner of the park,
hatches may not begin until the first of July and last most of the month. These mayflies are in just about
every stream in the park if not all of them. It's one insect everyone that fly fishes for trout should become
very familiar  with if they expect to be consistently successful.
Copyright 2012 James Marsh
Pale Morning Dun: