|....................... .................... ...Fly Fishing Yellowstone National Park
New KISS Bug Series - Part 29
Spotted Sedges (Caddisflies)
The Spotted Sedge pupae (hydropsyche species) are eaten by trout during the hatch more than the adults
when they are laying eggs or hatching. It's the easiest time for the trout to eat these caddisflies. They drift
in the current a relatively long time before reaching the surface skim to emerge. In the Firehole River and
Madison River, t he hatches will start taking place during early June, if not already.
When it approaches the time of year for the particular species of hydropsyche to hatch, the larvae will go in
their shelters and seal the openings. There they will proceed to spin a cocoon to use to pupate. It takes
about two or three weeks for them to form the pupa's cocoon and pupate.
At the time the hatch begins, the pupa will eat its way out by chewing a hole in the cocoon. It will then
proceed to swim to the surface to hatch. This is the time that the trout can easily pick off the pupae. They
have no trouble eating the helpless pupae drifting in the current trying to reach the surface to hatch.
These caddisflies emerge in moderate speed water. From the time they escape their cocoon and begin
their accent to the surface they are carried downstream by the current. The pupae are in this helpless
situation for some time. When they reach the surface of the water, the pupal shuck splits and the emerged
adult caddisfly quickly flies away.
The trout can also easily pick them off during the time they are emerging from their pupa shuck in the
surface skim. The bottom line to this is that these caddisflies are eaten from the time they emerge from
their cocoon until they fly away to streamside foliage.
The emerging process usually starts late in the afternoons and continues until well into the night. The egg
laying activity of the adult females from previous hatches will actually start during the time other caddisflies
Once you see any of the adults and know the hatch has started, you want to start fishing an imitation of the
pupa late in the afternoon. These caddisflies emerge from the riffles and runs of pocket water and from the
moderate flowing water of smooth flowing streams. If you are catching trout on a pupa imitation, then you
should continue using it until you start seeing trout eating the egg layers. This is usually very late in the
afternoon, well after the sun has set. At that time you may prefer to change to an imitation of the adult.
Some anglers fish the pupa imitation of the Spotted Sedge using a strike indicator. Although this method
will catch some trout, I think you would probably be better off fishing without an indicator. If you are fishing
smooth water, then I suggest you use a down and across presentation. You may need to weight the fly
to help get it down. You should also mend the line a time or two to help get the fly down. When the fly gets
almost directly downstream of your position, just stop the downstream drift by stopping the swing of the rod.
The current will bring the fly to the surface where you want to leave it for a few seconds.
Availability to trout:
Type of water:
Duration of hatch period:
Moderate to slow - smooth and broken surface