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's
a Drunella species commonly
called a Small Western Green
Drake or more often, a Flav.
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 taking place. Caddisflies
and stoneflies are also very important in
Yellowstone. That said, however, it's certainly not
an insect to ignore by any means.
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's worth imitating the combination at times.
Baetis, species, called Blue-winged Olives are
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 multi-brooded, meaning they hatch
twice a year. There's 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 a little 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 if 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
both the duns and spinners on the water in the
mornings. The hatch usually occurs during the
Pale Morning Duns:
There are two Ephemerella species, the inermis
and infrequens, or Pale Morning Duns. They 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's what most anglers probably think it is
unless they 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.
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 things
considered, it's only important in the lakes. There
it's the most important mayfly. Every stage of this
mayfly's 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
Tricos or Tricorythodes species can be found in
the Madison River. This is because this section
of the river is the actually 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 part of the 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 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. The spinner fall usually occurs near dark
but can occur in the early morning, sometimes
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 prior to the 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 a "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 this mayfly's 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 afternoon.
Copyright 2012 James Marsh
The Isonychia Nymph is a large
swimming nymph. They are
available for trout to eat.
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.
The PMD or Pale Morning Dun is
considered by many to be the most
important hatch in the park.
Flav or Small Western Green Drake
A tiny Trico Spinner on James'
finger shows just how small they
really are. Note the partial shot of
a wedding ring.
A tiny Trico Spinner on the top of
James' finger and a Trico shuck
in the center.
Another species of Blue-Winged
Olive. These are very plentiful.
Rare Image of a Gray Drake Dun
Gray Drake Spinner
Click on image to enlarge
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Something overlooked by most all anglers
are the hatches of the Paraleptophlebia
species.. 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's
necessary to use long, light leaders and
tippets and make very careful approaches.
This is tough fishing but can be extremely
productive in the late Summer and early Fall
in low, clear water conditions that are usually
referred to as to tough conditions.
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's 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's a nice,
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's little difference
in the behavior of these and the other clinger
nymph mayflies. These are usually a hook
size 16 to 18.
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:
The Cinygmula reticulata or Dark Red Quill
hatches in August and September in some of
the park's streams. It's probably the most
plentiful Cinygmula species but it's 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's a mid day hatch that
usually last a very short time.
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 don't hatch on the
surface. They will float down the streams in
the cold water for a few feet before departing
the water and the 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 Leadwings 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 are not a productive
stage to match. They don't 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 presented
will some action imitates these strong
swimmers better than a dead drift.
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