Flies are meant to trick fish into believing that they are eating a live organism.
Most flies are made to look like a specific organism that a certain species of
fish is used to seeing and eating from their natural environment. Trout eat a
lot of things, but average size trout mostly eat insects. Trout normally target
certain insects when they are concentrated, and most available.
Most insects have short lives, and are most concentrated when they are
hatching, or mating, or laying eggs.

The dense hatches create the most interest. Dense hatches of large insects
usually create the most interest for large trout. In the fall, inch and a quarter
long giant caddis flies hatch from nearly every river and stream in the Pacific
Northwest. Many of these hatches comprise thousands or maybe even millions
of these flying moth-like insects.

They have lived in a stream for a full year as a water breathing larvae. Most of
these large caddises hatch in to winged adults during the early fall, but some
cold spring creeks have hatches through much of the winter and into the
spring as well. The fat bodies of winged adults are in colors that range from
light tannish orange to yellowish orange to bright orange to burnt orange.

Wings are usually gray but there are also brown tones. There are apparently a
number of different sub-species in what is commonly called October Caddis or
Fall Caddis or Giant Caddis. Most belong to the family Dicosmoecus. Along
the Pacific coast they range from California to Alaska. The larva of these giant
caddis build tube-like cases.

During the winter months when the larva are tiny, these cases are made from
vegetable matter attached to a foundation of silk. As the larva grows in size
through the spring months they abruptly switch to cases made from small
gravel. You can observe these larvae crawling around on the stream bed
dragging their cases with them as they forage for algae and decaying plant
and animal matter. Many people call them periwinkles. During the summer

months of June and July Dicosmoecus larvae are important trout foods. Daily
behavioral drift cycles occur in the early afternoon, usually peaking about 4
p.m. They are one of the few families of caddis that leave their cases before
behavioral drift cycles. This makes them extremely enticing to large trout.
In August these larvae seal themselves in their cases and by September they
are ready to emerge as adults.

Emergence occurs from late afternoon until dark. The pupae usually swim and
crawl to shallow water, but some emerge mid-river. Many actually crawl from
the water to hatch on rocks along the shore.

Even when adults are not active, you can tell if October Caddis have been
hatching by observing their shucks on stream margin rocks.

If prospecting with a dry October Caddis pattern doesn’t turn up any interest,
try a pupa pattern.

Pumpkin orange color is usually the best.

Try fishing your pupa suspended from a dead drifted dry fly.

This technique can be very productive late in the evening when both egg
laying adults and hatching pupas are both active.

Steelhead as well as trout can be fooled by this trick.

Egg laying occurs in the afternoon and evening. The big fat juicy females flop
around on the water exuding their eggs.

They are a prime attraction for fish of all sizes.

Fishing a big orange body dry fly can be productive any time of day if you fish
in shady spots under overhanging trees.

Some caddis are active during moderate temperature days. Most of the big
caddis rest in the shade of vegetation throughout hot days.

These caddis are perfectly camouflaged to hide during the day and wait for
evening flights.