Mayflies of Yellowstone National Park

Baetis Nymphs are plentiful in
most of the streams of
Yellowstone. Notice the tiny,
short center tail. These are
swimmer nymphs.

This spinner is one of the
Heptagenia Group of mayflies
sometimes called Pale Evening
Duns. It was found in the
Yellowstone River during the
month of September.

Mayflies of Yellowstone:

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

The "Flav" is one of the more
common mayflies in the park. It is
a Drunella species commonly
called a Small Western Green
Drake or more often, a Flav.

A Green Drake Nymph is a large
crawler nymph. They are available
for trout throughout the season.

A wide variety of mayfly nymphs
exist in most of the streams in
Yellowstone National Park.

Several families of mayflies are plentiful in
Yellowstone National Park. Imitations of mayflies
are over fished by most anglers that fish the
park's streams and everywhere else for that
matter. They often tie a mayfly dun pattern on
when there isn't a hatch. Caddisflies and
stoneflies are also very important in Yellowstone.
That said, however, it is certainly not an insect to
ignore by any means.

Brown Duns:
Ameletus species, called Brown Duns exist but
are really not that plentiful. They hatch out of the
water and the nymphs are the only stage that
could be important to anglers. We don't consider
it of major importance. These swimming nymphs
look very similar to the Slate Drake nymphs which
are more prevalent. An imitation of it would work
for either mayfly nymph. For that reason, we think
it is worth imitating the combination at times.
Blue-winged Olives:
Baetis, species, called Blue-winged Olives are
fairly common in the park. The most important
species is probably the Baetis tricaudatus but
they are others. The Baetis tricaudatus and other
Baetis species are bi-brooded, meaning they
hatch twice a year. There is a late spring, early
summer hatch and then a fall hatch.
Some anglers think the nymphs are not very
important but we think differently. The nymphs are
eaten by trout to a large extent and especially just
prior to a hatch. To make it more complex, the
trout also eat the emerging nymphs, duns and
spinners. These mayflies usually hatch in the
early afternoons. Cloudy, overcast days are by far
the best types of days for this hatch. Most spinner
falls occur in the late afternoon but they can occur
early in the morning depending on the species
and weather. Some species of these dive to
deposit their eggs.
Little Blue-Winged Olives:
These are the Diphetor and Plauditus species
also called Blue-Winged Olives. We prefer to call
them the Little Blue-Winged Olives. These range
in a hook size from 18 to 24. There are also
some Acentrella species we categorize in this
group. These are usually a hook size 20 to 26.
They prefer the slower or moderate water. They
can be important where water flows out of a lake.
These mayflies can be bi-brooded and even
tri-brooded in some cases.
Small Blue Winged Olives:
Attenella margarita or Small Blue-Winged Olives
are found in a few streams in Yellowstone. They
prefer slow to moderate water. It appears they
like streams with aquatic vegetation but we are
not sure that is a requirement. They can be
important because they are a late season hatch.
These look a lot like baetis mayflies but these
have three tails and are therefore fairly easy to
distinguish. The nymphs, emergers and duns
can be important is the hatch is intense enough
to warrant it. We have not seen a spinner fall and
assume it occurs during the night. You may find
the duns and spinners both on the water in the
mornings. The hatch usually occurs during the
late morning.
Pale Morning Duns:
There are two Ephemerella species, the inermis
and infrequens, or Pale Morning Duns are found
in just about every, if not all of the streams in
Yellowstone National Park. These are crawler
nymphs and prefer slower to moderate water.
They are usually found in very plentiful quantities
in most streams. These range from a 16 to 18
hook size. This is the most important species of
mayfly in the West. They not only are plentiful they
also hatch over a long period of time. All of the
stages of life are important. We suggest that you
have nymphs, emergers, duns and spinner
imitations of this mayfly. The spinners can fall
both in the mornings and afternoons.
Great Blue-Winged Red Quills:
The Timpanoga hecuba hecuba, or Great
Blue-Winged Red Quill is found in a few streams
of Yellowstone. This is a large mayfly that can
easily be confused with the Green Drake. In fact,
that is what most anglers probably think it is if
they don't closely examine it. They occupy slow to
moderate water that usually has a soft or silty
bottom. Slough Creek is one of the locations for
this mayfly although there are others.
The nymphs, emergers, and duns can be
important stages to imitate. We have not seen a
spinner fall of these mayflies and assume that it
occurs after dark.
Small Western Dark Hendricksons:
There are some Serratella tibialis, or Small
Western Dark Hendricksons that can be found in
some of the park's streams. This is a late
summer hatch that may be important because
other hatches have ended. All stages of life can
be important to imitate.
This mayfly usually hatches in the middle of the
day. The spinner fall occurs late in the day, just
before dark.
Speckle Wings:
Callibaetis species called Speckle-wings, hatch
in calm water, mostly lakes. There are certain
locations in a few of the park's streams where
this mayfly can be found but all in all, it is only
important in the lakes. There it is the most
important mayfly. Every stage of this mayflies life
can be important to imitate. Trout eat the nymphs,
emerging nymphs, duns and spinners. The hatch
usually occurs in the late morning. The spinner
fall often occurs at the same time.
Tricos:
Tricos or Tricorythodes species can be found
only be found in one stream - the Madison River,
just inside the park as far as we know. This is
because this section of the river is the upper part
of Hebgen Lake. Every stage of life of the Trico
can be important but the morning spinner fall is
usually the best time to fish this hatch.
Western Green Drakes:
The Western Green Drake or Ephemerella
grandis is one of the larger mayflies that is
available in most of the park's streams. They can
get the trout going big time. They are available in
most of the streams in the park. You can find this
mayfly from July to September in the park
depending on the stream. All stages of life are
important to imitate. They prefer cold, fast flowing
water. The hatch usually occurs mid-day,
depending on many factors and the spinner fall
usually occurs near dark but can occur in the
early morning, sometimes before daylight.
Brown Drakes:
We have also spotted an occasional Brown
Drake, or Ephemera simulans in the meadow
sections of the Gibbon River. They prefer smooth
water. They are not that prevalent anywhere else.
The nymphs are burrowers. We do not think the
nymphs are very important until it is time for the
hatch. Then they can be important to imitate. They
emerge and the spinners fall is low light
conditions, usually after dark. This sometimes
occurs during the late afternoon (especially if the
sky is cloudy) and early evenings.
Small Western Green Drakes (Flavs)l:
The Small Western Green Drake, or Drunella
flavilinea, usually called Flav is common in
Yellowstone Park. This is a crawler nymph like
the big Western Green Drake just much smaller.
It usually follows the Green Drake hatch. All
stages of the mayflies life is important to imitate.
The hatch usually occurs during the late
afternoon and is usually short unless the sky is
overcast or cloudy. The spinner fall also occurs in
the late afternoons.
Slate Cream Dun / Pink Lady:
The Epeorus albertae, is one of the park's clinger
nymph mayflies. The female of this species is
called the Pink Lady. This hatch is best imitated
with a wet fly because the duns hatch on the
bottom or between the bottom and the surface.
They do not hatch on the surface. They will float
down the streams in the cold water for a few feet
before departing the water and they trout will take
some from the surface very aggressively even in
the colder water. Most anglers prefer a dry fly
imitation and the dry imitation of the dun will work
most of the time, just not as effectively as the wet
fly. These mayflies usually hatch in the late
afternoon.
Great Western Leadwongs or Slate Drakes:
The Isonychia species or Slate Drakes are fairly
plentiful in many of the streams of Yellowstone.
These are large swimming nymphs. The duns
hatch out of the water on the bank and rocks and
is not a productive stage to match. They do not
hatch in any concentration, rather periodically
throughout the day. The spinner fall which
happens near dusk or after can be important if
there are enough flies falling in the water to get
the trout's attention. A larger nymph will some
action imitates these strong swimmers better
than a dead drift. Little Wooley Buggers will even
work.
Mahogany Duns:
Something overlooked by most all anglers is the
hatches of the Paraleptophlebia species like the .
These hatches can be prolific. They are small
dark colored mayflies usually a size 18 or less.
These mayflies can be found in slow to moderate
water. Often it is necessary to use long, light
leaders and tippets and make very careful
approaches. This is tough fishing but can be
extremely productive when late summer and early
fall, low, clear water conditions are referred to as
to tough.
Western March Browns:
The Western March Brown, or Rhithrogena
species provide more important mayfly hatches.
These larger clinger nymphs hatch throughout
the day over a long period of time. It is rare to find
a large number of them hatching at any one time.
Sometimes, swinging a wet imitation of the
emerging nymph in the fast water where they
hatch is more effective than fishing the large dun
imitation. The spinner fall can be important in the
evenings provided it is a nice, warm day.
Pale Evening Duns:
Species of the Leucrocuta, Cinygma, Nixe and
Heptagenia genera, more commonly referred to
as the Heptagenia Group of mayflies usually
called Pale Evening Duns, exist in the park's
streams. These clinger mayflies can be prolific at
certain elevations and times of the year. There is
little difference in the behavior of these and the
other clinger nymph mayflies. These are usually
a hook size 16 to 18.
Gray Drakes:
Several of the streams in Yellowstone have the
Gray Drakes or Siphlonurus species. These are
found in Slough Creek in large quantities. They
are a swimmer nymph. They like slow to
moderate water with vegetation. The nymphs
crawl out of the water to emerge so the dun is not
that important. The spinner fall can be. It usually
occurs in the late morning but can occur near
dark.
Dark Red Quills:
Cinygmula sp
The Cinygmula reticulata or Dark Red Quill
hatches in August and September in some of the
park's streams. It is probably the most plentiful
Cinygmula species but it is rather scattered in
distribution. We have not found any significant
hatches but we understand they can occur. We
have only found the mayflies in small quantities
and only in isolated areas. It is a mid day hatch
that usually last a very short time.

Copyright 2008 James Marsh

The Isonychia Nymph is a large
swimming nymph. They are
available for trout to eat.

The Green Drake is one of the
largest mayflies in Yellowstone.
This insect can really turn on
the fish. The dun is the most
important stage to imitate.

Blue-winged Olives are very
common in the part's streams.
Some species are bi-brooded
and provide action for the angler
during both the early season and
fall hatch. The little swimming
nymphs are available year round
however. As you can see from
this image, some of the
blue-winged olives are very small
when compared to the thumb and
forefinger. This one lit on my shirt.
If you are not sure of the size, a
good size of fly to start with would
be a 20. Anything larger will
probably be too large.

This is a Callibaetis spinner.
They are plentiful in a few of the
streams in Yellowstone that have
slow moving water as well as
most of the lakes.

The Green Dake Nymph is a
large mayfly clinger nymph
plentiful in most of the streams in
Yellowstone. Like most mayflies,
the time it hatches depends
greatly on the elevation of the
stream. This one was found in
the month of August in the
Northeast corner of the park.

Slate Drake Spinners, an
Isonychia species, is the only
fishable stage of the hatch. The
duns hatch out of the water.

If you look closely you can see
the two tailed mayfly. This image
was captured during the month of
August on the Yellowstone River.

A beautiful cream colored
mayfly that we think is a Pale
Evening Dun. Since we didn't
capture it, we are not for certain.

We have not identified this
mayfly nymph for certain. It was
one of hundreds found in the
Lewis River. It would have been
a great place to fish a nymph.

This dun is from one of the
Heptagenia Groups of mayflies.

Slate Drake Nymphs, are
swimmers. They dart around
much like a minnow. Trout eat a
lot of these nymphs. .

Another species of Baetis
nymph: Trout eat a lot of these
where they are available and that
is all of the park's streams. These
are small swimming nymphs.