Little Yellow Stonefly
August 13, 2015
My first exposure to the small, yellow-colored stoneflies of Isoperla bilineata, or the Yellow Sally, came many years ago during my teen years in the mountains of northern Pennsylvania on Kettle Creek. Kettle Creek flows nestled in the deep folds of the Black Forest Mountains of Potter County in north central Pennsylvania. The Kettle's steep mountain valley was the scene of extensive logging at the end of the 19th century, and the virgin hemlock, white pine, and hardwood stands were cut clear to supply the rapidly growing cities of the East Coast. The lumberjacks' crosscut saws and double-bit axes swept over the mountains of north central Pennsylvania like a brush fire consuming nearly all of the standing timber, moving from area to area, and leaving behind a barren landscape that would take many years to heal.
Today the forests have regenerated but still show faint scars from the lumber era boom, with log slides cut into the mountain edges and railroad grades still visible to the trained eye coursing the wooded valleys where the narrow-gauge Shay locomotives of the Lackawanna Lumber Company pulled their log cars and Barnhart loaders along the steep cuts and switchbacks of the tight valley. Relics of the past still can be found in the form of discarded ax heads, log chains, and railroad spikes rusting away in the shade of the quiet woods.
The once sprawling boomtown of Cross Fork, with a population of over 1,500 residents, declined nearly as rapidly as it grew and is now only a tiny village of several dozen full-time residents. The little river once home to native brook trout was nearly decimated by the greed of the lumber barons' axes and saws and would take many years for the valley to return to a natural state.
The native trout would be pushed into the headwater streams of Hammersley Fork, Cross Fork Creek, Windfall, the Little Kettle, and the Germania Branch. Fortunately the mountains and valleys have healed well with theâ€¨passage of time and are once again home to black bear, bobcat, whitetail deer, and trout. The populations of wild brook trout never returned to the little river and were replaced by European brown trout, which thrive today, creating an often spectacular fishery with most of the classic Eastern hatches and creating an abundance of opportunities to challenge anglers.
On that June day when Charley Brown and I pulled on our waders and rigged our rods, the excitement alone was nearly more than a teenaged boy could stand. It was my first fly-fishing trip to the north woods of Potter County and my first baptism in the cold waters of Kettle. The evening sun was still high in the sky when the first hatching Isoperla stoneflies began to appear and the brown trout began to feed aggressively on them. The pale yellow flies skipped across the surface in their attempts to become airborne and were taken greedily with splashy rises of the hungry fish as dozens of trout began to work the hatch steadily until darkness overtook the valley and the Kettle once again flowed quietly. Our evening was one of both frustration and futility as neither Charley nor I had any suitable imitations in our boxes to match them.
The following morning we went to the local fly shop to find flies to match the stoneflies that had frustrated us the prior evening and found only variations of the Adams tied with yellow bodies, which were poor imitations at best. The flies worked with limited success but were refused by fish in calmer waters that had more time to inspect our offerings.
In those days Catskill-style dry flies still dominated most fisher's fly boxes, and it would be several years before down-wing imitations would begin to gain acceptance. My initial reaction to the problem of the Yellow Sallies was to more closely match the color of the naturals by toning down the body color to more of a butter yellow, and replace the traditional Adams hackle recipe of brown and grizzly with a lighter mixture of pale ginger and chinchilla. These flies worked well in the riffles and pocketwaters but still did not work over difficult fish in quieter currents. The gradual acceptance of down-wing imitations and new materials suited to tie workable flat-wing styles would trigger the next phase of my experimentation with adult stonefly imitations.
The inspiration came to me one afternoon in the 1980s when I was spending a few days as a guest at the Texas Blockhouse Fish and Game Club in northern Pennsylvania, where my longtime friend Charley Brown worked as a warden and caretaker. The clubhouse is perched on the edge of a hill overlooking two small streams that flow on either side of it: Texas Creek on one side and Blockhouse Run on the opposite, which join downstream from the clubhouse to form the Little Pine Creek. The club has a long and rich history of serious outdoorsmen, including Herbert Hoover, and has miles of superb trout water.
We had spent the morning on the club water, where I had caught one of the stoneflies and spent some time studying the form of the insect, and the solution to a longstanding problem of imitating the little stones flashed through my mind. Fortunately I had brought my tying kit along. A good imitation needed to match the coloration closely, but more importantly it needed to sit close to the surface and float on top in broken water. The fly also needed to be more robust than a mayfly dun pattern and have the low, flat wing profile of the natural insect.
At the kitchen table, I quickly dressed the fly that I would fish for the next 20 years with great success. The Z-Lon underwing sparkles as sunlight passes through it, and the elk hair provides enough stiffness in the wing to help keep the Z-Lon fibers flat over the fly's body to preserve the wing profile and improve floatation. Trimming the light ginger hackle flush on the underside of the hook allows the fly to float low in the film for selective fish. I made several more of the new pattern and tucked them into my fly box, eager to try them the next day.
The next morning, Charley and I were on a stretch of the stream where the bedrock ledges at the foot of the mountain valley turned the course of the currents in an abrupt hairpin turn, which fanned out into a flat pool. The far edge of the pool was retained by an old wooden cribbing wall, and a few low trees overhung and shaded its depths. The morning mist was just beginning to lift from the water's surface when I strung the little rod, fitting a light leader to the tip of the fly line, and finally one of the new yellow stonefly imitations, well greased with a floatant paste. The calm currents were broken from time to time with the soft rises of fish beginning to work a mixture of flies, and several fish were rising regularly. The first fish in this stretch occupied the tailout of the pool.
I cautiously crept into position below and across from the trout and worked out enough line to reach it. The little stonefly pattern settled on the surface quietly several feet above his position, and the fish came lazily to the fly when its drift reached him. The new stonefly imitation disappeared in a quiet swirl, and the fish bolted when it felt the sting of the hook. I worked the brown carefully to the side to keep him from moving up the pool and putting down the other fish. After resting the pool for several minutes, I cast to the next fish, which was holding tight against the cribbing wall, and the stonefly gently dropped in his drift lane. Again, the fish took the fly without hesitation.
I handed Charley a few flies, and we spent the rest of the morning enjoying success with the new pattern, beginning what would be a long stretch of similar results.
The yellow stoneflies of the Isoperla genus inhabit many of our smaller Eastern freestone streams with gravel bottoms, clean water, and high levels of dissolved oxygen. The nymphs live in the crevices between stones where they feed on smaller organisms. These small stoneflies enjoy a long emergence period, often showing on the water from mid-May well throughout much of the summer in the East, as well as in many Western states.
The adult flies are a yellowish color overall, often exhibiting a greenish cast, and the wings are held flat over the back and extend past the abdomen when at rest. The stonefly has short legs, and as a result sits very close to the surface of the water, with most of the body in contact with the film, which produces a different light pattern on the surface of the water than that of a mayfly dun. The females are slightly larger than the males, measuring 12 to 14 mm, while the males average 10 to 12 mm. Both sexes are well matched with patterns tied on 2X long dry-fly hooks in sizes 14 and 16. In low water conditions where fish tend to be more skittish I use size 18 hooks.
Emergences are often nocturnal, and Ernest Schwiebert's later release of Nymphs as well as Stoneflies by Doug Swisher, Carl Richards, and Fred Arbona present these hatches as being a nighttime activity. While this is generally true, I have witnessed hatches of these flies during evening hours on a number of streams as well as sporadic hatches throughout the day. Egg-laying activity brings the adults back to the stream and creates another opportunity to fish imitations of them. The flies typically hatch sporadically but can from time to time hatch in numbers significant enough to induce strong rises in the fish.
Due to the emergence patterns of these yellow stones, the trout never seem to become highly selective toward them, but they are fond of the flies and take them whenever the opportunity presents itself. Because of this, I often search the water with a Little Yellow Stonefly when nothing is hatching. Our days on the water are too limited by life's demands to waste the middle portion of the day, and fishing a search pattern can often provide a satisfying way to optimize fishing time, especially in pocketwater and riffles.
My favorite technique to fish these flies is with a 7 1/2- to 9-foot leader, depending on the stream's size, tapered to a 5X tippet, and with the fly presented in the drift lanes between stones in the pocketwater and the seams where slower and faster currents meet, and drifted over any likely looking holding lies. Fish in these types of water will often rush the fly provided the drift is good, and the rises are usually fast paced.
Henry Ramsay is a guide and fly-tying instructor at TCO fly shop in Reading, Pennsylvania. This article is an excerpt from his book Matching Eastern Hatches (Headwater Books, 2010).