Copyright 2013 James Marsh
Hatches and Trout Flies for the Big Horn River, Montana
As we mentioned before, the aquatic insect population isn't as diverse as many Montana trout
streams but the insects there exist in very plentiful quantities. One insect there in huge
quantities is the midge. Trout can be taken year-round on imitations of the midge larvae,
pupae and adults. During the winter months, that is what most of the fishing in the Big Horn
comes down to - midge fishing. Most of the time you need to be fishing a larva imitation right on
the bottom, or a pupa imitation right under the surface if a hatch is occurring. At times, during
heavy midge hatches, trout can be taken on adult imitations on the dry fly. Winter fishing will
vary with every passing cold front. The weather will range from sub-zero temperatures to as
high as the low sixties. The water below the dam will remain relatively constant.
Starting mid March through April and May, and sometimes the first couple of weeks in June, the
Big Horn will see large hatches of Blue-winged Olives. Other than midges, these small mayflies
will represent almost all of the insects that hatch during this time. Trout can be taken on nymph
imitations of the BWOs during the mornings and up until the hatches occur during the warmest
part of the day, usually early to mid afternoon. You will need to switch to Perfect Fly BWO
emergers with or without the trailing shuck during the early part of the hatch. Trout can also be
taken on imitations of the duns after the hatch is fully underway. Spinners are effective during
the falls. These mayflies are bi-brooded and will hatch again in September, October and the
first of November.
June and July both provide Little Yellow Stonefly hatches, called Yellow Sallies by most
anglers. Fish can be taken on both the nymph and adult imitations. Fish the nymph up until the
egg laying activity starts and then you may want to change to the dry fly adult imitation.
During June, July and the first of August the PMDs, or Pale Morning Duns will start coming off.
Fish the PMD nymph up until the hatch starts in mid-morning and then change to an emerger
imitation. When the trout start taking the little mayflies on the surface, you may want to change
to the dun imitation.
From the middle of July through September, hatches of Grannon Caddisflies, or Little Black
Caddisflies occur on the Big Horn River. These are normally called Mother's Day hatches but
take place long after Mother's Day on the Big Horn. From the middle of June until the middle of
August you will find huge hatches of Spotted Sedges taking place. This is the most important
caddisfly on the river. Little Short-horned Sedges will also hatch from about the middle of July
until the middle of August. July, August and the early part of September brings on hatches of
Green Sedges. The most important stage of this caddisfly is the larva, imitations of which are
called Green Rock Worms. They are effective flies to use anytime on the Big Horn.
Scuds and sowbugs both exist in the Big Horn River in very plentiful quantities. It is one of the
most important sources of food for the trout. Our imitations of both the scud and sowbug work
especially well on this stream and are very effective throughout the year.
Terrestrial are somewhat important, especially during high winds, but maybe not as important
as they are on many Montana trout streams. Imitations of beetles, ants and grasshoppers will
catch trout during the summer months.
Don't overlook streamers. The river has plentiful quantities of baitfish, minnows and sculpin.
Streamers are very effective on the large brown trout, especially during overcast days, or early
and late in the day.
Our Perfect Fly imitations are the most realistic and effective flies you can use on the Big Horn
River. We have imitations of everything that hatches or exist there. If you haven't already done
so, we invite you to try them. We are confident you will use nothing else once you do. I failed to
mention the lowly cranefly, but the Big Horn River has plenty of them, and the trout will eat our
imitations of the adults and their larvae. Our Perfect Fly imitations of the craneflies are the best
you can buy. We hope you give them a try on your next trip to the Big Horn River.
Big Horn River, Montana
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