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Stonefly Genus Skwala (Large Springflies)

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The genus Skwala (Short-winged Springflies) of the Perlodidae family is represented by three species in North America, Skwala americana, the identical looking Skwala curvata and Skwala compacta. Skwala should be included in any comprehensive list of important stoneflies for the western flyfisher. Though often mistakenly thought of as members of the Perlidae (Golden Stones) that happen to hatch early, they are actually quite different and often far more important on many western rivers than their more publicized cousins. Perhaps the most significant factors regarding this growing recognition are their inhabiting tailwaters previously too warm for trout and the lengthening of trout seasons, both relatively recent phenomena. This explains the scant mention they have received (if any) in older angling literature.

Excepting the lake dwelling compacta, they are lovers of cobble bottomed riffles and runs of larger mid to low elevation rivers. Their behavior is consistent with other large stoneflies except that they are more prone to floating long distances as they placidly oviposit, and with the exception of Pteronarcys californica (Salmon Flies) in some locations, they do it in larger numbers. There is usually no challenge to them for the fishes attention until Rhithrogena morrisoni (March Brown) mayflies begin to appear a few weeks later. Their flights occur during the warmest part of the day which usually means in the afternoon, though impressive flights have been observed around the lunch hour. Regardless, they finish well before dark.

The river dwelling adults have smoky brown to brown wings, brown legs, and either primrose (often tinged w/ olive) abdomens ribbed with brown or the reverse in darker strains. The males are brachypterous (Brachypterous: With short or or addreviated wings.), smaller and usually darker. Both sexes thoracic (Thorax: The thorax is the middle part of an insect's body, in between the abdomen and the head, and to which the legs and wings are attached.) ventrals are a curiously marked yellow/dark brown variegated pattern. Gravid females carry blackish pea shaped egg clusters off the tips of their abdomens that are much larger in diameter.
  

Where & When


Regions: East, West

Time Of Year (?): late Winter through Spring, depending on location

Preferred Waters: cobble riffles in large rivers

Altitude: mid to low level
In CA, their emergence runs for a few weeks to a month or more and can start as early as mid January, depending on the year. Years with cold Januarys and/or lacking an early February "false spring" can delay them until the end of February or even running well into March. These dates are much later north of Southern Oregon and east of the Sierra's. They are reported even later in the northern Rockies.

Hatching Behavior


Habitat: cobble riffles and runs

Skwala are terrestrial (Terrestrial: Insects which live on land and are fed on by trout only when they incidentally fall into the water are known as "terrestrials" to fly anglers, and they're very important in late summer.) emergers like all the large stoneflies. What is different about them is their preference for privacy even after emergence. They are hidden in the crevices of cobble instead of clinging to open exposures of large rock or riparian plant life. This can perhaps be explained by their emergence so early in the year before the shore cobble builds up too much daytime heat. They will go completely unnoticed by all but the most astute anglers and observers until their mating flights begin, seemingly to materialize out of thin air. In years of abundance, they can come in clouds of insects within minutes.

Egg-Laying Behavior


Time Of Day: Warmest part of the day

Habitat: Same as emerging
Their dark bodies coupled with their flush floating posture make them very difficult to make out on the water, in spite of their size. Adding to this difficulty is their placid behavior. They never seem to flex and flap wings as their larger relatives do. Their presence on shore side rocks is the first alert, followed by seeing them in the air and even crawling on you. You won't usually see them on the water, but when you see them everywhere else and fish working, it's time to fish the dry fly. Ovipositing flights seem to be dependent on sunshine and calm conditions which are usually not the most prevalent late Winter and early Spring. This may explain their smaller numbers after previous wet blustery seasons and the astounding populations that build up when warm drought years string together.

Nymph Biology


Current Speed: moderate to fast

Substrate: cobble

The female nymphs run 18 to 22 mm in body length with tails and antenna as long as their bodies. The males are substantially smaller. In build and markings, they superficially resemble the larger Perlidae (Golden Stones), but are less stout and colored a bit differently with greater contrast between ventral (Ventral: Toward or on the bottom.) and dorsal (Dorsal: Top.) surfaces. The larger western perlid nymphs tend to be dark patterned amber (think oak turkey wing) dorsally over a paler yellowish amber to tannish ventrals; Skwala nymphs are even darker patterned brown (turkey tail) over pale olive or amber.

Pictures of 3 Stonefly Specimens in the Genus Skwala:

Female Skwala curvata (Large Springfly) Stonefly AdultFemale Skwala curvata (Large Springfly) Stonefly Adult View 2 PicturesThis female dropped her eggs just before this photo was snapped. The distinctive notch in the subgenital plate identifies the species. An interesting observation is how active they get when exposed to direct sunlight. Trying to stage this specimen was most difficult. In the shade it would calm right down, but when exposed to direct sun it would immediately go nuts, scampering all over quickly without pause. Perhaps this explains why they don't seem to be found out and about on overcast days, but if the sun peeks out... She was 24 mm long, head to wingtip.
Collected March 22, 2013 from the Lower Yuba River in CA
Added to Troutnut.com by Entoman on March 27, 2013
Skwala (Large Springflies) Stonefly NymphSkwala (Large Springflies) Stonefly Nymph View 2 Pictures
Collected March 5, 2005 from the Jocko River in Montana
Added to Troutnut.com by Bnewell on June 28, 2011

Recent Discussions of Skwala

Skwala 9 Replies »
Posted by Entoman on Jan 16, 2011
Last reply on Nov 2, 2011 by Sayfu
The genus Skwala (Short-winged Springflies) of the Perlodidae family should be included in any comprehensive list of important stoneflies for the western flyfisher. Though often mistakenly thought of as perlids (Golden Stones) that happen to hatch early, they are actually quite different and often far more important than their highly publicized cousins on many western rivers. Perhaps the most significant factors regarding the growing recognition of their importance are their inhabiting tailwaters and the lengthening of trout seasons, both relatively recent phenomena. This goes a long way in explaining the scant mention they have received in older angling literature.

Where Skwalas are found in such incredible numbers are mostly the low elevation tailwaters. These rivers flowed much too warm in the Summer and early Fall to sustain trout fisheries prior to the extensive dam projects of the 50's and 60's. So... nobody in our fraternity paid much attention to the bug life. Whether the Skwalas were already there and adapted to the cooler water or migrated from higher elevations is an interesting conjecture. A popular theory is that these tailwaters are rapidly evolving ecosystems that are only now settling into their established fauna that include the now very important Skwala and ... trout! It makes sense to me.

In CA, their emergence runs for a few weeks to a month and can start as early as mid January, depending on the year. Years in which we miss a February "false spring" following a cold January can delay them until the end of the month running well into March. These dates are undoubtedly much later north of Southern Oregon and east of the Sierra's. They are reported even later in the northern Rockies.

What little information that does exist about the genus Skwala in flyfishing literature is often misplaced with other genera or treated in short footnotes as insignificant. There also seems to be a lot of confusion among knowledgable anglers between this genus and Paraperla, which is of an entirely different family (Chloroperlidae). Ernest Schwiebert in his revised addition of "Nymphs" listed Paraperla paralella as a hatch of some significance out west. In footnotes related to this species, he mentions that some entomologists are considering placing this species in the Skwala genus. This footnote is the only reference to Skwala in the entire book and the genus isn't listed in the extensive index covering hundreds of far more obscure species. His comment only adds to the confusion. Especially since he accurately describes Paraperla's physical characteristics, which are at odds with those of Skwala. Moving species among genera while retaining their specific names is one thing but moving them to entirely different families already in existence is problematic. Perhaps the confusion comes from shared specific names by the two different genera in older taxonomies that do list Skwala paralella as a valid name that has since been dropped.

What we call them aside, there is no confusion about the differences in their appearance. Paraperlas are very slender (not unlike the dark winter stones) and less noticeably segmented than would normally be associated with Perlodids. They are more monochromatic and usually lack pronounced patterning on their dorsal surfaces. They cannot be mistaken for the much stockier and stipple backed Skwalas, who's tails and antenna are also more than twice as long.

Because of this confusion over nomenclature maybe reports by anglers of "Skwalas" from other regions of the West that are described as strongly olivaceous in color are in fact referring to Chloroperlids and not Perlodids? This needs to be sorted out.

Lovers of large cobble bottomed riffles and runs, their behavior is consistent with other large stoneflies except that they are more prone to floating long distances as they placidly oviposit... And with the exception of the pteronarcids (Salmon Fly) in some locations, they do it in larger numbers. There is usually no challenge to them for the fishes attention until the March Browns (Rhithrogena morrisoni) begin to appear a few weeks later. Their flights occur during the warmest part of the day which usually means in the afternoons. I have also fished over impressive flights around the lunch hour. They finish well before dark.

The female nymphs run approx. 22 mm in body length with tails and antenna as long as their bodies. The males are substantially smaller. In build and markings, they superficially resemble the larger Perlids (Golden Stones), but are less stout and colored a bit differently with greater contrast between ventral and dorsal surfaces. The large perlid nymphs tend to be dark patterned amber (oak turkey wing) dorsally over pale amber ventrals; Skwala nymphs are even darker patterned brown (turkey tail) over primrose.

The adults have smoky brown wings, brown legs, and primrose abdomens ribbed with brown or the reverse. The males are brachypterous (very short winged). Their curiously marked sternites are perfectly matched by the yellow/black variegated chenille when its wrapped on a hook (to bad it doesn't float well). Gravid females carry black, pea shaped egg clusters off the tips of their abdomens that are larger in diameter than their abdomens. Folding a section of black foam to stick out beyond the hook bend is a wise addition to some of your dry imitations in case you find fish attracted to the those that have yet to drop their eggs.

Unfortunately, another trait they share with other large stonefly genera is their propensity for cyclic population densities. Frankly, many of the western large stonefly genera appear to be in a down cycle from their peaks of a few years ago in a lot of locations, and their present populations on some of the rivers I fish are nothing like the "blizzards" we saw in the 70's.








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