Copyright 2013 James Marsh
Hatches and Trout Flies for the Yellowstone River - Outside
Yellowstone National Park
As with most other trout streams, one of the most important aquatic insects on the Yellowstone
River is the Blue-winged Olive. These little mayflies start hatching around the first of March and
last until the middle of May. They are bi-brooded, or hatch twice a year, and show up again
about the first of August. This second go round can last through October.

Probably the next important mayfly on the Yellowstone River is the Pale Morning Dun. They too
hatch over a long period of time, starting about the middle of July and lasting until as late as
the middle of September.

Another mayfly that hatches in some sections of the river is the Gray Drake. It starts hatching
about the middle of July and can last until the middle of September, depending on the location.
There's also some Flavs, or Small Western Green Drakes, that can be found in some areas of
the river. They too start hatching about the middle of July. This hatch is usually over by

Caddisflies are often the most important insects. One of the first to hatch are the
Brachycentrus species, or Little Black Caddis. This hatch is called the "Mothers Day Hatch". It
starts about the first of May and last for only a couple of weeks. There are other hatches of
Little Black Caddis that occur from about the middle of July through the month of August.

The Spotted Sedges are the most plentiful caddisfly species. These caddisflies start hatching
around the middle of June and last until the end of July. Little Sister Caddisflies start about the
middle of July and last through the month of August. Little Brown caddisflies start hatching
around the middle of July. This hatch usually last for about a month, depending on the location.

About the middle of June you will find two important species of stoneflies hatching. The
Salmonflies start hatching then and last until the near the end of July, depending on the
location. The Golden Stonefly starts about the same time and last until the end of July, again,
depending on the exact location. Both of these hatches can be affected by the spring runoff.

You should always have a good selection of streamer flies. The river has plenty of minnows,
baitfish species and sculpin. Streamers work great early and late in the day and when the
water is stained from heavy rains. They are also effective when the water is off color from the
runoff, after the really bad water passes through.

Terrestrials become very important during the months of July, August and September.
Imitations of ants, beetles, and grasshoppers work great at times. Grasshopper are especially
important because of all the hay fields around the Yellowstone River. When the wind blows and
the farmers are cutting hay, a lot of these insects get into the water.

Use our "Perfect Fly"
hatch chart and select your flies for the time you will be fishing. Please
give our flies a chance to work for you if you haven't done so already. We are confident that
you will be by glad you did.
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Yellowstone River, Montana
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