What is a Skwala? Know your Flyfishing Bugs

What is a Skwala? 
Reports have been coming in from guides, social media, and across shop counters and by many estimates the peak of the skwala hatch is upon us. Sounds like a perfect time to get in-depth about what the old-timers call the “olive stonefly” and entomologists call “Skwala Americana”, “Skwala Curvata” or “Skwala Compacta”.

Cling on, you crazy diamond.
Skwala nymphs are diamonds in the rough come spring on the Bitterroot.

These olive-shaded harbingers of spring are a welcome sight for western Montana fly fisherman, as they herald the real beginning of dry fly season. In the all-too-short window between winter and spring runoff in western Montana, the skwala stonefly reigns supreme, and with good reason – though the skwala is present on a select few other river systems, (such as the Yakima river in Washington) the sheer numbers and bulk of the hatch on the Bitterroot and lower Clark Fork rivers is unrivaled. The number of bugs might be large, but the knowledge base among fly anglers lags behind like a three-legged greyhound. Let’s take a shot at alleviating that problem.

This adult stonefly probably feels pretty lonely. Maybe he’d like a trout to keep him company.
Photo via troutnut.com

Like the rest of the stonefly family, or plecoptera, the skwala has a two-stage life cycle. For most of their lives, skwalas live as bottom-clinging nymphs and closely resemble the more common golden stonefly nymphs. Big and bulky nymphs 18 to 24mm long with amber-yellow coloration, they hatch from eggs underwater and mature for a year before crawling to shore to split their nymphal shucks and emerge as adults along the shoreline.

Upside down is no way to live life. This is the trout’s eye view of a skwala.
Photo via troutnut.com

What truly makes the skwala unique among the stoneflies are their desire for privacy- unlike their more prominent family members, the skwala adults seek out crevices in the rocks, the undersides of cobblestones and other areas of cover for their hatching. This behavior marks the skwala hatch, and it’s elusiveness more storied. Because of this, the skwala adults can sometimes seem to appear from out of nowhere- though observant anglers will find huge numbers of the nymphs if they seek them out.

What triggers the emergence for skwalas is temperature and sunlight, which is why the skwala hatch can begin as early as February, and run into late April. Though the exact temperature that gets the nymphs moving is debatable, without a doubt, when water temperatures reach the mid 40s the bugs begin appearing. When water temperatures hit 50 degrees, the hatch is surely on.

After hatching and finding a mate, females return to the water to deposit their eggs, though this stage is often practically invisible. Fly fishermen would do better to seek out bugs on the shoreline rather than looking for their presence in the air or on the water.

Adult skwalas have smoky brown bodies, highlighted by the olive markings that they have become famous for. A dark grayish-brown pair of wings lay flat along their bodies when not in flight, though the wing is often splayed out as the bug struggles in the water. The adults are wiggly, slow swimmers and patterns that imitate this low-riding dog paddle will turn trout heads.

Though the skwala hatch generates loads of excitement and anticipation among anglers, those who know it well tend to temper these dreams with the knowledge that the hatch is less a spectacle than a subtle thrum. Look for single adults swimming if you must, but don’t be surprised to find bigger numbers along the shoreline during the peak of a hatch.


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