Sub Family: Dicosmoecus
Trophy trout are not an accident. Water chemistry, trout population densities, angler regulations, structure, and forage base all play key roles in this intricate puzzle. Even in waters known to house large trout a stimulus in the form of prey items is required to lure them into chasing the fly. Large trout need calorie rich prey to maintain their mass. In many instances this means feeding on large morsels. On many western rivers and streams October Caddis adults, pupa and larvae match this criteria to a tee. When these large bugs are active rainbows, browns, cutthroat even returning steelhead seldom pass up the chance to snatch a few.
October Caddis belong to the Limnephilidae or Northern Case Maker family, a widespread group with over 300 species populating rivers, streams and lakes. Larvae of this family are case makers constructing intricate cases from a variety of materials. Anglers wishing to become caddis confident can identify specific species by the materials and manner in which they put them together to form their signature cases. Many species within the Northern Casemaker family grow to appreciable sizes.
Stark yellow and conspicuous when removed from their cases the grub like October Caddis larva grow big, capable of reaching sizes up to 35mm. The pale orange adults complete with the familiar tent shaped caddis mottled grey brown wings are somewhat smaller, averaging 30mm in length. Downsizing through stages a common aquatic insect trait and observant fly fishers can use this feature as a pattern size selection guide. Pupae mirror the adults in coloration, burnt orange or pumpkin in some circles bodies and grey thoraxes and wing pads. Pupa are large so wingpads, heads, eyes, legs and antenna are all worthy of imitation and subsequent consideration at the vise.
Fast moving freestone rivers and streams featuring rocky bottoms are prime October Caddis habitat. Many western rivers in British Columbia, Washington, Oregon and Northern California are home to anadromous populations of steelhead, Dolly Varden and cutthroat. These rivers are Dicosmoecus rich.
October Caddis, as their name suggests, lay their eggs at the surface during the autumn months from late September through early November, within days of their emergence. This practice differs from other caddis species that lay their eggs during the summer months when aquatic vegetation and algal growth is at the apex. Rich algal and weed growth provides a rich forage base for new born larva. Despite this apparent seasonal shift fly fishers should make note of those streams and rivers with greasy algae covered substrates as this conditions are ideal for generating plentiful Dicosmoecus populations. During the early stages of their 1 year larval cycle October Caddis inhabit slower moving reaches grazing on algae and rotting leaves. At this time larval case construction features neutrally buoyant materials such as leaves and small sticks that are easy to haul around. As the larva grow and mature they migrate to swifter stretches changing their case components to small pebbles and sand that help anchor them to the bottom debris these grazing caddis larva forage amongst. Although primarily grazers, October Caddis have an omnivorous streak and are capable of scavenging and preying upon other aquatic nymphs and larva. During one photography sampling expedition a Dicosmoecus larva made short work of an unsuspecting mayfly nymph in my sampling tray. During the daylight hours October Caddis can be seen on the sun warmed surfaces of rocks and boulders. As sun fades into night larva move, migrating to the undersides of the same rocks and boulders. Foraging trout rummage through the rocks picking the grazing larvae from their perches. Watch for the silver flash of trout in riffles and runs as an indication this feeding behaviour is taking place.
October Caddis, as with other aquatic insects, participate in a phenomenon known as behavioural drift, an activity where aquatic insects release their grip and drift downstream to re-establish themselves. This activity evenly scatters insect populations throughout the system. October Caddis larva approaching maturity often leave their cases during the June July period drifting downstream to construct new cases should they survive the perilous journey before contacting the bottom. Bright yellow Dicosmoecus larvae do not go unnoticed. Many perish, consumed by opportunistic trout and char. Larvae choosing not to abandon their homes drift case and all. Trout show no prejudice, consuming both case and the larva inside. Fly fishers wishing to take advantage of this habit should be on the water dead drifting their larval imitations in the late afternoon as this is the peak of the daily October Caddis drifting activity.
During the summer months mature larva move from the swifter stretches populating slower areas of the river. Here they often secure their cases to the rocks and enter an inactive biological stasis known as diapause. The larva is not does not begin the transformation process from larva to pupa at this time. It is believed this stasis concentrates the emergence process as immature larva within a given age class have a chance to catch up while advanced growth is curbed.
Approximately 2 months prior to their late fall emergence October Caddis begin the pupation process. Cutting themselves free from their larval chambers the pupae pre stage along the bottom and then crawl and swim toward shore in a clumsy almost stumbling fashion where they often emerge in the near shore shallows. A unique species that is difficult to generalize, October Caddis also emerge at the surface midstream or crawl completely from the water. Pay attention to shoreline rocks and debris for signs of an emergence. Peak emergences often occur in the late afternoon through the evening. When the hatch is on fly fishers should focus upon the near shore areas with both adult and pupa patterns as trout move in to these areas to feed. Particularly those areas featuring streamside vegetation as mating adults frequent these areas. If regulations permit a dry dropper set up of a pupa dangled beneath a large dry October Caddis adult imitation can be deadly. Try adding the odd strip to the presentation to both skate the adult and elevate the pupa pattern in the water column. This trick can be the ticket in coaxing finicky trout to the fly. If fishing pupal patterns solo make a point of keeping the offering near the bottom.
Despite their concentrated 2 -3 week emergence habits October Caddis do not hatch in blizzard proportions associated with their smaller caddis cousins. The primary trout and subsequent angler attraction is their large average size. Size 6 adult and pupa patterns are common on many western rivers and streams.
October Caddis typically mate within 2 days of emergence. Mating in the same manner as other caddis copulating Dicosmoecus adults join at the rear of their abdomens, unable to come apart until mating is complete. Paired adults finding their way onto the water’s surface offer a large target that is seldom passed upon if trout or steelhead are in the area. As with other caddis species October Caddis are capable of scurrying around on the surface, creating a substantial wake. On many of the west’s summer run steelhead streams skating and waking large October Caddis patterns across runs and tailouts draws immense steelhead to the surface exploding on the fly with heart stopping toilet flush rises.