The Skwala Stonefly ~ Identification, Behavior, Fly Patterns, and Presentations

As fly anglers, we all look forward to dry fly opportunities. It truly is the epitome of fly fishing, and why I relocated from Graeagle to Nevada City to be able to fish and guide the best winter dry fly fishery in the state – The Lower Yuba River. After spending 27 years living above 5,000 feet with 6 of those years at 10,000 feet, I can truly appreciate the milder temps of the foothills of the Sierra. The Lower Yuba River is well known for its winter hatches, where BWOs, PMDs, and Brown Duns make a daily appearance along with a special stonefly too. Enter the Skwala. Unlike a tiny winter stonefly, the Skwala is much larger and the first big meal of the new year for trout. It’s an overrated hatch for sure with promises of stellar action on the surface, but to me it is one of the most intriguing hatches that grace our tail waters and freestone river systems of the Northern Sierra.

This family of stonefly, Perlodidae, is same as the Yellow Sally stonefly, and a very important species inhabiting most watersheds in the North American continent. They are often mistaken for early instars of Perlidae (Golden Stones), which they closely resemble. The most notable differences between the two families are the perlodids have much longer tails and antennae, and usually a more slender appearance. 

The male Skwala is much smaller than the female at 13-15mm, and the female, a robust 18-22mm size that is a requirement to be able to carry the hundreds of eggs she will be ovipositting as an adult. The color of the nymph is a yellow/olive with hints of brown for camouflaging. They live beneath the surface for 2 to 3 years molting into several new instars as they grow before reaching maturity. The adult’s color differs from when it is first hatched, to near the end of its life. A freshly hatched Skwala on the LYR will be a brighter yellow/olive, and as it ages, it ripens like a banana and takes on the color of golden spicy mustard. The wings of the Skwala stone are mostly clear with a smokey tinge, and thickly veined. On the Truckee River, the color of a Skwala adult is a true olive and more typical of Skwala populations that reside in the West. A stonefly can live a long time for an aquatic insect, up to 2 months as it can eat and drink water, unlike a mayfly with its 24 hour life expectancy.

Skwala nymphs are predaceous and will eat smaller mayfly nymphs, free living caddis, and midge larva. Both male and female Skwala nymphs when fully mature will start staging in the idle side water downstream of major riffles about a month prior to emergence. Water temperature, and lunar cycles trigger the nymphs to crawl out in the darkness of night to cobblestones next to the bank, often some will crawl well over 30 feet from the side water. They follow other Skwala nymph’s scent pheromones which they trace to livable spaces under the cobblestones. They split their nymphal shuck and emerge into a winged adult resulting in an incomplete metamorphous. Immediately, the males seek out females to mate with, and no time is wasted during this effort. Often while flipping cobblestones on dry land searching for the adult you will find a group of them mating. During night time and cold periods, they reside underneath the larger cobblestones. As the sun warms the surrounding cobbles through solar radiation, they crawl out and sun themselves until warm enough to actively crawl and sometimes fly. Skwala stones are most active from mid-day until late afternoon. They love sunny days and will often hide and protect themselves under the cobblestones during prolonged periods rain, and cold weather.

When walking the bank while searching for active rising trout, I always keep an eye on the surrounding willows. When I do see swarms of Skwalas in the willows, it’s a good clue on where to concentrate your fishing efforts. Adult Skwalas can mate several times through the time period they are alive. Most crawl from spot to spot, or float downstream with the currents, and at times will fly to relocate themselves, lay eggs, or to find a new mate. It takes on average, a few days to a week for eggs to develop inside a female Skwala stone. The eggs are then pushed out to the tip of her abdomen and are held in place until ready to be deposited in the water. 

The egg ball consists of dozens of smaller eggs held together in a sack, the ball is sparkly and shiny and black in color and easy to identify to the naked eye. Most females will crawl to the water’s edge, enter the water, and drift placidly down with the currents while ovipositing their eggs. Other females may fly over the water and splash down to achieve the same result in ovipositing. 

It takes a period of time in the early stages of the Skwala hatch for trout to key in on both the nymphs and adults, and also to recognize when Skwala adults are most active. Once the trout dial it in, they will swim into the side water around noon time next to the bank where Skwalas will be in the drift of the foam lines, and wait patiently to intercept them. While drifting, the legs of a Skwala stone are very active as they kick them back and forth. This is a trigger mechanism for trout, and why rubber legs on fly imitations are an important component for Skwala patterns.

Cast less, and observe more for greater success

As mentioned above, there are also good populations of Skwala stones on the Truckee River as well as the East Walker, and the Wild & Scenic Middle Fork Feather River. On the Yuba, Skwala emergence is from the middle of January to the middle of March on average. As the hatch winds down in March the trout are used to seeing them day in and day out, and will continue to take artificial patterns presented properly. On the Truckee they emerge much later due to a higher elevation and an overall colder environment. The hatch on the Truckee generally is from the beginning of March to the end of April, and likewise for the MFFR, but often we see them well into May. On the East Walker, the Skwala stones are active from the middle of February to the end of March. These are general guide lines as weather, high flows, and lack of sunny days can greatly influence the emergence of the higher elevation Skwala populations.

Each river has local favorite patterns. Below I have provided a list of my “go to” nymphs and dry flies that imitate the unusual specific characteristics of the Skwala stone.

Nymphs:
- Jimmy Legs Stone #10-12, mottled yellow olive/coffee.

- Pat's Rubber Legs #10-12, mottled yellow olive/coffee.
- Mercer's Poxy Back Stone #10-12.

- John Barr's Skwala Stone #10-12.

Dries:

- Unit Skwala #10-12.

- Double Dutch Bug #10-12.

- Stimulator #10-12, yellow olive.

- Dan LeCount's Bullet Head Skwala #10-12.

On the left is the size 12 2xl Unit Skwala male, and on the right is the size 10 2xl female. This is the freshly hatched color I use. 

This is the aged color of a Skwala adult with its more spicy mustard appearance. Male on the left, and the female on the right.

Presentations for nymphing are straight forward and standard with your typical indo rig, or tight line set up. Targeting specific water downstream of riffles and obtaining a dead drift is much more important than a particular pattern. For dry fly presentations, I typically use a standard upstream approach while searching, and when a rising fish is encountered I will then use a fly first downstream presentation. The “standard” presentation for fishing a Skwala dry fly involves making a cast upstream and stripping in line with your line control hand as the fly rides the currents back down towards your stationary position. Line control and keeping slack to minimum is critical. In this scenario there are no rising fish, and the angler makes a series of “fan casts” from near to far in order to effectively dissect a small section of the river before moving upstream to explore fresh unmolested water.

“The Reach Cast” is considered to be a very technical presentation, and is often used to highly educated trout because it delivers the fly first. Simply meaning that a rising fish only sees the fly as it enters its cone of vision. This presentation is best executed by being upstream and across from your acquired target. The angler makes a series of false casts that is aimed slightly downstream towards the rising fish, this allows the angler to gauge the correct distance of line needed. On the final forward cast, while the line is still in the air, the angler moves the tip of the rod upstream. In doing so, it provides an aerial mend, and the fly lands first with the leader and fly line trailing upstream of it. Once the fly, leader, and line make contact with the water, the angler brings the rod tip back downstream and begins paying out line using the “Bump Feed”. Also known as stack mending, line is dispersed from the tip by moving the rod up and down, while the line control hand feeds the guides of the rod with a specified amount of fly line. Again, line control will dictate your success. Too much slack will result in a missed take, not enough slack will drag your fly during the drift, and the trout will refuse your fly. An adult Skwala drifts on the surface with very little movement, except for those twitchy legs.

                              

 

                                   

The allure of fly fishing to the different hatches we encounter is the fine tuning of our approach to each unique individual species. From their behavior, to the flies we tie to imitate them with, it’s the intricate details that count. I often find the study of these aquatic insects and their connection to the natural world far exceeds the actual fishing. I’m truly grateful for these experiences…

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