Giant Fall Caddis: A Trout’s Last Big Meal Before Winter

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Giant Fall Caddis: A Trout’s Last Big Meal Before Winter

By: Rick Hafele

A big one in the net that ate an October Caddis Pupa fly.

When the short days of fall arrive so does one of the last “big” hatches of the year. The giant fall caddis provides one more opportunity to fish big dry flies for large trout.

Most of a trout’s food in the fall comes in the small to tiny size range. Tiny blue-winged olives of the genus Acentrella (family Baetidae) hatch on cloudy afternoons, their light gray bodies barely five millimeters long, make even a size 20 dry fly look like a giant. Mixed in with these little mayflies float midges of various types often so small that the tiny upright wings of the mayflies hide them on the water. Caddis too seem to shrink in size with the shrinking daylight of fall. Little saddle-case caddis (family Glossosomatidae) that provided fast action in May make an appearance once more from mid-September through October, and if you can match them with a size 18 pupa or dry fly consider yourself lucky.

The frustrating thing is that trout like these tiny morsels and one often finds it necessary to go to smaller and smaller flies for any chance of success. Fortunately, just when you have given up trying to thread that size 22 compara-dun onto your tippet, out of the trees flies a giant; a big lumbering insect with four wings and long antennae. The giant caddisflies of fall have come to save the day.

Adult October Caddis.

It’s the October caddis, also known as the fall caddis or giant orange sedge. October caddis, of the family Limnephilidae, belong to the genus Dicosmoecus. These large caddisflies standout like an NBA player at a midget convention, and they have some unexpected habits that one must be aware of to fish them successfully.

Recognizing the different species of caddisflies is hard enough, but caddis in the family Limnephilidae can be really tough as it’s the most diverse family of caddisflies with 40 genera and close to 300 species in North America. This means a quarter of all North American caddisflies belong to this single family. They have also adapted to a wider range of habitats than any other family of caddisflies including a few species that shun water altogether to live in moist terrestrial conditions. Fortunately the large orange bodied adults of the October caddis are hard to miss and look quite distinct when seen flying among the other small adult insects common in the fall.

Dicosmoecus is primarily a Western genus that includes five species, two of which – D. gilvipes and D. atripes – are the most common and can make up a large part of the cased caddis found in many western trout streams. The cases of young larvae consist mostly of plant material – leaves and twigs laid lengthwise – then quite suddenly they switch to cases made of mineral material producing a stout case of small gravel. The cases of full-grown larvae may reach one and half inches long, are slightly curved and have little to no taper from front to back. If you remove a larva from its case you will see multiple gill filaments along a cream to light yellow abdomen and a dark brown to black thorax and head.

October Caddis larva on the bottom of a river in early summer.

Dicosmoecus larvae spend a lot of their time on the tops of large cobbles and boulders in moderately fast currents grazing on diatoms or shredding leaves trapped on the bottom. As mid summer approaches larvae begin congregating together in bunches where they attach their cases to the substrate and seal off both ends. The benefits of larval aggregations prior to pupation are not clear, but such behavior occurs in a variety of other caddisfly families. Inside the sealed cases the larvae enter a diapause or resting period until late summer when they finally molt into pupae. Pupal development then takes several more weeks to complete.

As pupation draws to a close the behavior of Dicosmoecus diverges from most all other caddisflies. First they emerge at night, something many other caddisflies do. But what is unusual is the way they do it. Most caddis pupae cut out of their protective cases and swim to the water’s surface where the adults emerge and fly away. Pupae of the large October caddis however do not swim up to the surface. Instead they swim along the stream bottom until they reach protruding rocks along the stream bank, sometimes taking several minutes or more to make the trip. At the stream edge the pupae crawl up the sides of the rocks and the adults escape the pupal shucks several inches or more above the water. Empty pupal shucks stuck to the sides of rocks provide clear evidence of this nocturnal transformation.

Hatches of Dicosmoecus may start in early September in higher elevation streams, but most don’t usually start until mid to late September and then continue throughout October. Of course the exact timing of hatches depends on local weather and stream conditions. Adult Dicosmoecus adults have orange bodies with light to dark gray wings. Adults are active flyers in the late afternoon and evening when the females return to lay their eggs on the water’s surface.

October Caddis shucks after the pupa crawled out to hatch mid-stream.

Knowing the behavior of the large fall caddis provides the key to fishing their imitations successfully. There is little doubt that trout feed on the cased larvae as they crawl along the stream bottom. How often and how important this is to the fly fisher may be open for debate, but there is no debate that large cased caddis nymph patterns fished deep along the bottom will catch some nice trout. This can be particularly true after a heavy rain that raises the water level and knocks the cased larvae into the drift. The best time of year to fish cased larva patterns is from mid winter through spring. The availability of the cased larvae ends in early to mid summer when the larvae seek shelter and attached their cases firmly to the substrate for pupation.

The next opportunity to take fish is when the pupae begin their migrations toward shore for adult emergence. Because emergence occurs at night (anytime from just after dark to just before daylight), there is debate about how often fish see and feed on the pupae. Still, enough anglers have success fishing pupa patterns that trout must be seeing them and may even be on the lookout for them throughout the day. Remember these are large pupae, ranging from three fourths to an inch long, and thus provide fish with a lot of protein as they prepare for winter. Because these large pupae are not swimming to the surface like most caddis, but swimming along the bottom towards shore, you need to switch your tactics. Instead of using a typical Leisenring lift for wet-fly swing, you should fish these pupa patterns along the bottom and let them swing close to shore where a slow retrieve upstream several feet often proves effective. To get your pupa patterns to the bottom you will need weighted flies and possibly some weight on your leader as well. Fishing two pupae in tandem can also help get them down and increase your odds. Pupa patterns tied on 10’s and 8’s will be needed to match the naturals. The pupae have a yellow to golden brown abdomen with dark brown to black thorax and head.

October Caddis pupa ready to emerge is pumpkin orange.

Adults live two to three weeks, during which time they mate on streamside foliage. While not attracted to water until they are ready to lay their eggs, wind and rain can put many adults on the surface at various times during the day. Dicosmoecus adult activity increases rapidly in the late afternoon and early evening on crisp fall days when females return to lay their eggs. During this activity I’ve experienced both frustration and success. On some streams (like the Deschutes!), for reasons unknown to me, trout seem to completely ignore the large fluttering adults, while on other streams I’ve fished trout can’t seem to wait to get a mouthful of a fat Dicosmoecus. Some anglers have mentioned to me they have good success fishing large adult patterns wet when their dry offerings have failed. Something to keep in mind and worth trying whenever adult caddis patterns fail to get a rise. Even when dry fly patterns fail, however, I’ve found trout will still be interested in pupa patterns fished slowly close to the stream bottom.

Fishing an October Caddis pupa fly with a 3-weight Spey Rod.

We should thank nature for providing one last chance to attract large trout with surface flies we can actually see before winter arrives. The large caddisflies of fall are special in many ways, not the least of which is their ability to attract trout.

Favorite October Caddis Patters:
Pupa: Morrish's Deep October Pupa #6, #8
Dry: Stimulator, Kaufmann's Orange #8
Steelhead: Berry's Milf Steelhead FlyTwitcher Steelhead Waking Fly

Rick Hafele has been observing bugs and fish for over 40 years, and has been contributing Checkout his most recent books, videos, and available club programs at https://www.rickhafele.com

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