Caddis are not one insect. Trichoptera is an order with hundreds of species on Western trout rivers, and the "Caddis" line on 85 of the 92 river charts here is shorthand for a season-long parade of different bugs: the black Mother's Day caddis of April and May, the tan spotted sedges of summer evenings, the green free-living caddis in the riffles, and the big orange October caddis of fall. What they share is a life cycle with no dun and no spinner, a pupa that trout eat more of than anything else, and an adult that lives for weeks and keeps coming back to the water. If you learn the pupa, you have learned most of what matters.
Larva, pupa, adult: why there is no "hatch" to match
Caddis are closer to moths than to mayflies. The larva lives on the bottom for most of a year, either in a case it builds (Brachycentrus a square chimney of plant fibers, Glossosoma a saddle of pebbles) or free-living and net-spinning like Hydropsyche and the green Rhyacophila. When it is ready, the larva seals itself in and pupates. The pupa then cuts its way out, fills with gas, and shoots to the surface, and the adult breaks out and is airborne within seconds. Trout rarely get a clean look at an adult during emergence, which is why a dead-drifted dry caddis during a hatch so often gets ignored while a pupa swung or lifted through the same water gets hammered.
The adults are the part anglers see: evening swarms over the riffles, bugs in the willows, egg-layers skittering on the water. Adults live for days to weeks, so a river can have caddis in the air long after the emergence ended. When adults are on the water in the evening, the fish are eating egg-laying or spent females, and that is when the dry fly is right.
The Mother's Day caddis: Brachycentrus in April and May
The one caddis emergence that behaves like a true hatch is Brachycentrus, the American grannom, which comes off in dense clouds over a couple of weeks in spring. Five river pages here list it separately: the Provo below Jordanelle peaks in April and May, and the Middle Provo, Weber, Ogden, and Boise peak in May. The insect is a size 14 to 16 with a dark, almost black body and gray wings. The patterns on those pages are a Black Elk Hair Caddis and a Brachycentrus Pupa in 14-16, and the Provo and Weber add a Black Soft Hackle, which is the pupa fished the old way, swung. The Provo page also lists a LaFontaine Sparkle Pupa in 14, the pattern built specifically to imitate the gas-filled pupa on its way up.
The Arkansas in Colorado has the other famous Brachycentrus blitz, moving up the river from the canyon toward Salida in late April and May. Its chart lists caddis peaking May through August, so the Mother's Day bugs open a long caddis season there rather than getting their own line. On all of these rivers the emergence comes in the afternoon, and the dry fly works best in the hour before dark when the egg-layers return.
Summer caddis: Hydropsyche and the evening rise
From late spring through August the bulk of caddis activity on most rivers here is Hydropsyche, the spotted sedge, a tan to brown insect in size 14 to 16 that emerges in the evening. The river charts show it clearly: caddis peak April through June on the low tailwaters (Missouri, Bighorn, South Platte, Frying Pan, Upper Sacramento, Yakima), May through July on the Utah and Colorado freestones and mid-elevation tailwaters (Big Hole, Gunnison, Taylor, Roaring Fork), May through August on the Montana freestones (Bitterroot, Blackfoot, Gallatin, Yellowstone), and June through September on the Idaho and Wyoming mountain rivers (South Fork Snake, Lochsa, St. Joe). The Oregon coastal rivers run April through August.
The Elk Hair Caddis in 14-16 is listed on 78 rivers, the X-Caddis (a low-riding pattern with a trailing shuck) on 60, and the Goddard Caddis in 12-14, a buoyant spun-deer-hair fly for rough water, on 14. Those three plus a Soft Hackle in 14-16 cover the summer.
October caddis: Dicosmoecus on the steelhead rivers
The last caddis of the year is the biggest. Dicosmoecus, the October caddis, is a size 8 to 10 with an orange body. Eight river pages list it, all peaking in October: the Deschutes, Metolius, North Umpqua, Rogue, Clearwater, Klickitat, Methow, and Yakima. The flies are an October Caddis Dry and an Orange Stimulator in 8-10, and the Yakima adds a Buckskin Caddis. On the steelhead rivers, a skated orange dry in October is a steelhead method as well as a trout one.
Fishing the pupa
Tie a pupa (Sparkle Pupa, Brachycentrus Pupa, or a Soft Hackle) on the point and fish it three ways:
- Dead drift and lift. Nymph it under an indicator through the riffle, and at the end of the drift let the line tighten so the fly swings up through the water column. Most takes come on the lift.
- The swing. Cast across and slightly downstream, mend once, and let the fly swing on a tight line. The soft hackle's fibers pulse in the current. This is the method for the Mother's Day hatch and for any evening when adults are in the air but fish are not breaking the surface.
- Dry and dropper. An Elk Hair Caddis with a pupa eighteen inches below it, fished through the riffles at dusk. The dry catches the fish taking egg-layers; the dropper catches the ones taking emergers.
When fish are slashing and boiling but ignoring your dry, they are eating pupae inches under the surface. Switch to the dropper rig before you change dry patterns.
Evening on a caddis river
Plan the day around the last two hours of light. Fish nymphs through the afternoon, switch to the pupa when the first adults show over the riffles, and go to the dry when fish are taking adults on top. Skitter the dry when egg-layers are active; dead-drift it when spent adults are on the water. Carry a headlamp; the best of it is often after you can see the fly. The Provo, Weber, and Arkansas all have special-regulation stretches where the Mother's Day hatch is best, so check the Utah Division of Wildlife Resources or Colorado Parks and Wildlife before you go.