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Entomology

Brachycentrus

The Martha Stewart of caddisflies

If Martha Stewart were an insect she’d be a Brachycentrus. Their little homes are perfect. Most caddis grab a stick here or pebble there and glue together something that sort of resembles a tube and they call it home. The Brachycentrus (brack-ee-SENT-rus) will have none of that. They find the perfect stick and chew it down to the perfect size. In some creeks, pine needles are the building material of choice, in others it might be lodgepole bark and in still other waters it might be strips of sedge. Regardless what the material is, the Brachycentrus builds a perfect home. Their cases are shaped like chimneys that are slightly narrower at the base than at the mouth. The corners are mated to create impeccable right angles and the square profile is clean and neat. With all the power tools in the world I certainly couldn’t make anything so flawless, how can a damn insect do it with only it’s teeth?

Brachycentrus inhabit a wide variety of waters but seem to prefer rollicking waters punctuated with numerous back eddies and calm pools. Many authorities refer to them as strictly lotic (river) dwellers, but I have found them clambering along wave swept shorelines of high Sierra ponds.

Brachycentrus are not limited to moving on their own six feet. In our aquariums I’ve watched them over and again crawl up on the fizzing air stone to grab a bubble and hitch a ride on the ascending globe of air. When the bubble hits the surface, the larva envelops the bubble with its legs and somehow prevents it from breaking through the film and bursting. They will ride these bubbles for hours at a time.

I thought this was amusing but aberrant behavior caused by their unnatural environment until I saw the exact same thing on Rush Creek. The Brachycentrus were harvesting oxygen bubbles being released by aquatic vegetation. They would pluck the bubble (a byproduct of photosynthesis) and allow it to float them to the surface where they would drift round and round the slow eddy. This bubble harvesting technique must aid their dispersal drift. [Most aquatic insects drift downstream at periodic intervals. Called "behavioral drift", this practice spreads their numbers throughout a river system and insures their species won’t be annihilated should some catastrophic event impact a section of the system.]

Brachycentrus larvae feeding in algae

Brachycentrus gather much of their food by holding their legs outspread and filtering bits of debris from the current. These larvae are often found in tremendous numbers wafting amid clumps of filamentous algae with their second and third legs spread wide. They are also commonly found atop rocks with one lip of their house glued to the rock.

Thread spinning is well known among Brachycentrus. This thread is reportedly used as an anchor while the caddis rappels downstream, but I feel they use the thread more as a device to lower themselves into prime food collecting currents. On an eastern Sierra stream near June Lake I have observed several thousand Brachycentrus feeding while dangling by their silken threads. They would rappel into the confluence of two currents and while being buffeted about, would spread their second and third legs wide to gather drifting particles. After some amount of time (minutes to hours) these larvae would jug back up the threads to the point of attachment. I never once saw them rappel to a downstream perch.

The threads are strikingly visible and trout will swim through the tangle of threads with mouths wide open like baleen whales to inhale the hapless nymphs. The shiny thread is enough of a trigger that savvy anglers will brighten their tippet with white grease pen (Mean Streak brand) or typewriter correcting tape when fishing a Brachycentrus imitation.

As far as imitating the larvae in its log cabin case, I’ve never seen any specific imitation nor is one needed. A pheasant tail nymph seems to work just fine. The PT’s concentrically wrapped body that mildly flares to an abdomen with a few scraggly legs is close enough. Lighten a foot or so of tippet with Mean Streak grease pen then add a hefty split shot just proximal to the rod of the marked line.

Flip the fly across and upstream and allow the shot to hit bottom so the nymph dangles downstream on the taught white line. This technique was perfected on Truckee River in the early forties by anglers mimicking the free roaming Rhyacophila caddis larva that shares the Brachycentrus rappelling trait. When first developed, white sewing thread was used instead of marked up monofilament.

When time comes to pupate the Brachycentrus glues the lip of its case to a rock and seals up the mouth of the case with a silk door that quickly hardens. Safely snug inside, the larvae transforms into a pupa that matures over a period on one to two months. Upon emergence, usually in spring or very early summer, the pupa chews through the door and swims and crawls along the riverbed.

Unlike many caddis, the Brachycentrus pupa doesn’t seem to be a particularly strong and active swimmer. It allows the current to push it around at will and only occasionally will it attempt to reach some sort of destination. After an undetermined amount of time the pupa rises to the surface and drifts under the film. (It is frequently reported that Brachycentrus emerge from their cases then "shoot" to the surface. My observations indicate they can spend hours exploring the riverbed before ascending).

The Brachycentrus hatch can be incredible. This is the bug responsible for the famed "Mother’s Day" caddis hatch on the Yellowstone. This is the first super hatch of the year and anglers from around the country descend on Livingston praying that spring melt won’t blow out the fishing.

On selected rivers in California the Mother’s Day caddis hatch occurs with all the strength of the Yellowstone. In May of 1998 record snowpack was turning into record run off and fishing was terrible. On a hunch, Lisa and I went to a small spring-fed creek on the off chance it might not be blown out. We call this Caddis Creek, the maps call it something else, and you can call it anything you like should you stumble across its waters. . . just don’t write about it. Atop a hill in the meadow we looked down on the creek and from a hundred yards away could see working trout. Lots of them.

This creek creates wide blankets of foam in the oxbows and back eddies. The rising trout punched black holes in the foam as they rose to Brachycentrus emergers and ovipositors. The water was boiling with fish. Brachycentrus pupal husks formed ankle deep clots along the shoreline and windrows of drowned and drowning adults wafted in trailing streamers along the eddy seams. Beat up winged adults, returning from their egg laying chores, skittered across the surface towards shore. There wasn’t a footprint in the sand.

As is common with heavy Brachycentrus hatches, individual trout were keying in on specific phases of the "hatch".

Some fish were gently tipping up with open mouths breaking the surface, then tilting back down. These fish were taking dead ovipositing adults as well as crippled and dying emergers. Size 14 E/C caddis and chocolate and green soft hackles were taken without hesitation as long as the drifts were absolutely drag free.

Another segment of trout were porpoising through the film. This rise is often characteristic of fish taking emergers just under the surface. Indeed, the soft hackles and crippled caddis patterns failed miserably on these fish, but a green and brown La Fontaine sparkle caddis drifted under a greased leader connected with regularity.

The third group of trout were not really rising, but golden flashes underwater indicated trout were either grabbing ovipositing adults or ascending pupae. Knowing that both the pupae and swimming adults were carrying packets of air and actively moving about, a #14 Bird’s nests rubbed in powdered dry fly floatant, weighted with a split shot and given an active retrieve would have taken these fish. To be honest, we didn’t try. Who wants to nymph while fish are eating dries?

These guys missed Mother’s Day by a few weeks, but who cares. It couldn’t have been more perfect. Martha Stewart would have been proud.