The Pacific Northwest has some spectacular giant caddis hatches. Most of these hatches are in the 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 in a range from light tan to yellow to bright orange to burnt orange. Wings are usually gray but there are also brown tones. There are a number of different sub-species in what is commonly called October Caddis, Fall Caddis or Giant Caddis. Most belong to the family Dicosmoecus. They range from California to Alaska.
The larvae of these giant caddis build tube-like cases. During the winter months when the larvae are tiny, these cases are made from vegetable matter attached to a foundation of silk. As the larvae grow 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. 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 4:00 p.m. They are one of the few families of caddis that leave their cases before behavioral drift cycles which 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 pupae are 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.