Enlarged shot of the dark salmonfly nymph.
They look dangerous but they are not.
Flyfishingdvd's Imitating Aquatic
Insects: Stoneflies  
will teach
you what you need to know about
stoneflies and how to imitate
their behavior.  
.................................................Fly Fishing Yellowstone National Park
The Golden Stonefly adults
deposit their eggs mostly at
dusk or later. Fishing a dry
imitation can be effective latter
in the afternoons at times,
however, cloudy, overcast days
can  bring on the egg laying
activity  earlier in the day.
A large Salmonfly nymph from
the Firehole canyon. It don't take
many of these to fill up a trout..
A hand full of salmonflies indicates the
massive hatch in the canyon of the Firehole.
You will find that Yellowstone has a huge population and diversity of stoneflies.
Many of its streams are perfectly suited for them.

Importance as Trout Food:
In spite of the quantity of stoneflies in the streams, they are not always the most
important trout food available to the trout because of the word available. They are
not usually available. They are usually hidden down between and beneath the
rocks and stones that make up the streams substrate. When they feed, in some
situations; when they molt, in some situations; and when they hatch in all
situations, they are available for the trout to eat.

Occasionally, the smaller stonefly nymphs get accidentally caught by the streams
current and tumble downstream. Some, mostly the small species, are a part in
the behavioral drift. It's certainly possible to catch trout on an imitation of the
nymph at times other than during the hatch but it may well produce less than
satisfactory results.

The Hatch:
Stoneflies hatch out of the water, not in the water like most other aquatic insects.
Most all stoneflies crawl out on the shoreline, rocks or other objects that are
protruding out of the water to hatch. It is during this migration that they are most
available the trout to eat.

Imitating the Hatch:
You should imitate this behavior by retrieving your nymph imitation on the bottom
towards the bank. Fishing from the bank and retrieving your fly back to shore is
usually more effective than the typical nymphing on the swing and high sticking
type methods are. Keep in mind that the stoneflies move to the quieter water
along the shore or pockets where rocks extend out of the water as opposed to
crawling out of fast water. You want to fish the calmer portion of the water that is
adjacent to the fast water in which the stoneflies live.

Stoneflies live for a relatively long time out of the water. They mate out of the water.
Unlike mayflies, for example, stoneflies can eat and drink as adults. Just because
you find a lot of stoneflies in the bushes and trees along the banks of a stream
doesn't necessarily mean you can catch trout on an imitation of the adult. The only
time the adults are going to be available for the trout to eat is when the females
are depositing their eggs.

Egg Ovipositiing:
Most stoneflies deposit their eggs during the night but some species do so
during the daylight hours. All of them prefer to deposit their eggs during low light
conditions. Overcast skies and rainy days may offer some opportunities for
anglers to catch trout on ovipositing stoneflies.

Stonefly Families:
There are nine families of stoneflies in the United States. Wyoming has species
from all nine families. Many of the species in the park hatch before or after the
season closes and are not important. Unlike caddisflies and mayflies it's usually
not necessary to determine these to any level below the family level. With only a
very few exceptions, there is very little difference in the genera of the families. Most
all of them are about the same size and shape. The colors of the nymphs and the
adults within a family can vary within the family. In Yellowstone National Park, the
majority of the larger stoneflies are either the salmonfly or the golden stonefly.
These are not difficult to distinguish from each other or the other families of

The best way to choose a fly to match them in the event you are unable to identify
a hatch is to catch one of the adults and match it. If you have patterns of the type
we recommend, then you would have a fly to match them. You can find the adults
by checking the bushes, trees and grass along the stream side for the stoneflies.
The nymphs are also fairly easy to acquire. They can be found clinging to the
bottom of stones. Normally, you can pick up the stones from the bottom of the
stream and get a good idea as to what is most available in the stream. The
following are the most  important species:

Perlidae Family                       Golden Stoneflies:
Species of the "Golden Stonefly" family are probably the most plentiful group of
stoneflies in the park. The
Hesperoperla pacifica is the most common species.
Most of these are very colorful as nymphs. Patterns of dark brown and yellow
distinguish them, especially those that are near maturity. The adults range from a
golden dull yellow color to a solid brown depending on the species. Imitations of
the nymphs can be very productive prior to a hatch. Much of the egg laying activity
occurs after dark but late afternoons may produce some activity especially if low
light conditions exist.

Perlodidae                         Little Yellow Stoneflies
Species of the Isoperla genus of the Perlodidae family are usually called the "
Yellow Sally"  but several other species are also called Yellow Sallies, so that
depends on what part of the country you are in. The
Suwallia pallidula is another
species that is common in Yellowstone National Park. These stoneflies usually
hatch in the afternoons and usually begin to deposit their eggs late in the
afternoon prior to dark and continue to do for some time in the evening. This
makes it productive in most cases to imitate the egg laying activity before dark.
We have experienced very good results in some of the streams in Yellowstone
imitating the egg laying activity of the Yellow Sallies.

Pteronarcella Family:       Salmonflies
Pteronarcys californica
The giant salmonflies are plentiful in some of the streams in the park.  These are
huge nymphs that live for 3 or 4 years. Trout can be taken on imitations of the
large nymphs during the day during the hatch period, even though the large
stoneflies hatch during the evenings. Before they hatch they migrate to shore and
the trout are well aware of it. They follow the nymphs and feed on them for a few
days prior to the time they hatch.

Imitations of the adults fished during the eggs laying activity can be very effective.
Imitating the adults is not effective unless you fish at the right time. Just because
you see these huge flies in the bushes, doesn't mean they are depositing their
eggs. This activity usually takes place a few days after the hatch. Both the hatch
and the egg laying activity moves upstream as the hatch progresses.

Stonefly nymphs are in every stream we have checked in Yellowstone National
Park. Normally, they are very plentiful. Since the families of larger ones, the
Goldens and the Salmonflies live for 2 or 4 years, they are always in the streams
in all sizes. They are definitely a very important and abundant trout food in the
small and larger freestone streams of the park. It's true most of them stay hidden
most of the time. Only a few small species have been found in a drift. Trout may
have a hard time finding one to eat unless it is trying to crawl to a bank to hatch, or
the stonefly nymph gets careless feeding at night. There is one thing you can
count on, however. The trout know they are there and they are always ready and
willing to pounce on one whenever they get the opportunity.

Copyright 2012 James Marsh
A Yellow Sally  is one of the
more common stoneflies in the
park. The Little Yellow Stoneflies
are in the Perlodidae family.
The huge Salmonfly adults
deposit their eggs late in the
afternoon and on into the night.
The Golden Stonefly nymphs
are present in about all the
streams. Imitations of them
usually work good.
The huge salmonfly nymph is a
big meal for any trout. This one
is on the Gardner River. This
river has an excellent hatch.
Golden stonefly hatches can be prolific at
times on certain streams in the park.
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The Golden Stonefly nymphs are present in
just about all of the streams in Yellowstone
National Park.
Another Golden Stonefly
A pair of Salmonfly nymphs
The salmonfly adults hang
around in the bushes most of
the time during the day. The
females will be back on the
water before long, depositing
their eggs and fishing can be
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More Stonefly Thumbnails-Click on image
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