Skwala Stoneflies: The first big bug of the year
Western trout are hungry during spring. Skwala stoneflies are the largest and the most appealing item on the menu.
By Boots Allen

Spring is a much-heralded time for western U.S. trout anglers. This is when winter loses its grip on the land, the days grow longer, weather patterns generally stabilize, and fishing becomes a lot more comfortable and productive.

Accompanying that warming air and water temperature is the appearance of multiple aquatic invertebrates. Steady midge hatches join heavy numbers of blue-winged olive mayflies. The first thick emergence of caddis, and on some streams, March brown mayflies, appear. All that activity gets the blood flowing. But for many western fly-fishers, nothing beats the first large bugs of the year—skwala stoneflies.

In fact, skwalas give fly-fishers their first opportunity of the new season to break out boxes of stoneflies and large attractors, and cast easy-to-see surface patterns to rising trout. The skwala hatch doesn’t match the popularity of salmonfly, golden stonefly, or green drake hatches, which arrive later in the year. But for some dedicated anglers, skwalas are a focal point, and I know a couple people who chase skwala emergences from stream to stream over a six-week period from mid-March through early May. To help you imitate these early-season monsters, and make the most of your pre-runoff time on the water, here are a few considerations and tactics that have worked for me, year after year, on waters sprinkled around the West.

The Skwala

Skwalas are members of the Perlodidae family. There are three prominent species in western North America—americana, curvata, and compacta—however, there are only slight physical differences between the trio and it takes a close inspection to detect variations. Moreover, in their nymphal form, anglers could easily misidentify them as a golden stonefly. As adults, the most noticeable traits shared by all are a smoky-colored body (similar to a mahogany dun), a thick, dull orange stripe on top of the head, and black notches on the ventral side of the thorax. While skwalas are the first large stoneflies to appear on many waters, they are noticeably smaller than salmonflies and golden stones. Adults typically measure in at 18-to 22-millimeters long, though larger specimens approach 25 millimeters, and are most often matched with size 8 and 10 hooks.

Like most spring hatches, skwala emergences occur as water temperatures warm. There are variances from stream to stream, but for the most part hatches begin to hit their stride when water temperatures average between 46 and 49 degrees (F). The skwala emergence and lifecycle is similar to most stoneflies. Nymphs crawl from the streambed to surface rocks and vegetation—on dry land, their exoskeleton splits open and adults crawl out of their shucks. After mating, females return to the surface of the water to release eggs. Some bugs do this while flying, but just as many crawl from the bank to the current. They can be on the water for quite some time. Which is highly risky: As adults on the surface they are most vulnerable to trout.

The skwala is a prototypical “clean water” bug that favors rivers with moderate-to high gradients and ample cobblestone, which is most prevalent on freestone or freestone-like rivers. The pre-runoff window—that timeframe when water temperatures warm consistently above 40 degrees until snowmelt and runoff begin in earnest—typically lasts between four and six weeks on most freestone streams. This window coincides with a trout’s elevated spring metabolism. At this time, trout feed heavily, trying to reestablish the weight they may have lost over winter, and to prepare for the rigors of spring spawning (for cutthroat and rainbows). Skwalas are the largest food form emerging during later winter and spring (a boon to fly anglers) and while nymph patterns can hammer fish, the surface is really where it’s at.

Skwala Timing

Skwala water abounds in the western U.S., but each stream is different. Montana’s Bitterroot River has one of the earliest emergences in the Rockies. It typically kicks into gear in late March or early April, but has started as early as late February. A few years ago, I was lucky enough to hit the hatch on March 14 between the towns of Florence and Lolo. Someone said the hatch typically moves upstream at a consistent four to five miles a day under the right conditions, so had I fished the same section a couple weeks later, I may have missed the hatch altogether.

Other western Montana streams with very productive skwala hatches are Rock Creek, the Blackfoot River and the Clark Fork River. On the right day, all of these rivers may produce outstanding dry-fly action on rainbow, cutthroat and brown trout that average about 12 inches long and often stretch past the 20-inch mark. All of these streams, including the Bitterroot, are only minutes away from Missoula, which is western Montana’s fly-fishing hub and a town that’s got a serious addiction to trout and brewpubs.

On the other hand, the skwala hatch on Oregon’s Owyhee River has the reputation of being sporadic. But when it’s on, it’s really on. The height of hatch activity can be as early as mid-March during some years, though it generally reaches a crescendo in April. Another Northwest river, the Yakima in central Washington, hosts a skwala hatch that generally starts in early March and extends into April—Yakima fly-fishing veterans say the bug’s upstream progression can be molasses-slow. Although officially a tailwater, a number of tributaries feed the Yak and can limit dry-fly possibilities just before runoff. When that happens, anglers still have luck drifting nymphs under the surface.

Wyoming’s Snake River is my home turf and the waterway where I have the most familiarity with skwalas. Like the rivers mentioned above, local anglers pay close attention to what is happening with runoff and weather, trying to nail the best window for the hatch to take place. Many of my clients time a spring fishing trip to coincide with the bug’s emergence. Rightfully so—the Snake River’s hatch is intense and generally the last to appear in the West. It typically starts in mid-April and continues into mid-May. But the peak tends to occur with the first signs of runoff. It’s not uncommon for Snake River anglers to enjoy a solid week of fishing skwalas before watching the river turn to mud. But there are lucky years when the runoff arrives late, and excellent fishing with large surface patterns continues for three weeks straight.

That said, skwala emergences don’t end just because runoff starts. Most western freestones go through several 24-hour melt/freeze cycles before runoff hits in full force. Because of that, a stream might be off-color in the morning, but clear slightly around noon, and offer better fishing in the afternoon hours. Even if a river is off-color, fish on. Remember, you’re imitating big bugs that are easy for trout to see, and the fish are already keyed in on them.

Skwala Strategies

Fishing big surface bugs always seems pretty easy—toss it out there, work in a mend, maintain the drift, and set the hook when you get an eat. That’s simple enough.

Nonetheless, there are certain things you can do to improve your catch ratio when fishing big dry flies, especially those imitating skwalas. Focus part of your effort on presentation, and part on the water you’re targeting, because both are equally important.

For starters, remember, skwalas are movers and shakers. While some females fly to the stream to deposit eggs, many crawl from the banks and into the current to complete the lifecycle. When doing so, they create a wake on the water as they scurry along, and that attracts hungry trout. So, simply put, forget dead-drifts. Purposely move the fly after the initial mend. After that, retrieve slack and continue to animate the fly from side-to-side by twitching the tip of your rod. Intermittent dead-drifts help from time to time, but by no means should a dead-drift be the only type of presentation you rely on.

Second, target a wide variety of water types wherever skwalas hatch—just off the banks and near in-river structure. Skwalas emerge around these areas and some unfortunate bugs lose their grasp and end up in the water. Because they crawl from banks and structure and are carried along by the current, often while releasing eggs, many other water types can be productive. Riffles and long, flat pools yield good results. However, seams and current margins (where fast water collides with slower water) are perhaps the most productive water types. I’ve also noticed consistent action along seams created by channel confluences.

I’ve had some great action on seams separating the main current from slow pools or outright dead pools that have no discernible current at all. These seams are places where trout can rest on the current margin and still have access to drifting forage in the nearby, fast moving water.

Because skwalas emerge as water temperatures warm into the high 40s, it seems obvious that afternoons should be the prime times for fishing. This is no doubt true, but do not ignore the morning hours, even early morning. I have seen skwalas on the water as early as 8:30 a.m. on the Snake and Bitterroot rivers. These may simply be a significant number of females that emerged from the previous day. No matter, trout key in on these bugs, just as much as they do later in the day.


Skwala Silhouettes

Skwalas provide solid early-season dry-fly fishing with big surface imitations. The most popular patterns are size-8 and 10 variations of the Chernobyl Ant that feature fluttering wings and rubber or Flexi Floss legs. More traditional patterns, however, can be just as effective. Kaufmann’s Stimulator and the original Double Humpy are two of my favorites and most effective when intentionally skittered or moved across the surface. Some fly-fishers contend that the heavy hackle used on these patterns is key to their success. The hackle creates a wake that mimics the natural disturbance created by a skwala as it scurries along the surface. The legs on foam ant patterns can create a more natural silhouette, but the wake isn’t as imitative. I suggest hitting the water with heavily hackled patterns and legged flies so you can match whichever style the fish prefer.

Nymphs also produce, and I turn to them for a change of pace or to prospect for larger trout when fish aren’t eating on top. Like my adult imitations, I tend to go with size-8 or 10, short-shanked hooks when fishing skwala nymphs. A simple Pat’s Rubber Leg or a slightly more complex Flashback Hare’s Ear Nymph with rubber legs are two of my favorites. I target the same types of water I would with dries—banks and structure, confluence lines, current margins, heads of riffles/runs, and seams.

Fishing a skwala emergence can be fun. It’s hard to beat skittering a size-10 attractor across current to rising trout as the first rays of warm sunshine fill the spring air. Yes, you may need to deal with early runoff issues, and the possibility of a muddy river, but if your timing is right, fishing the skwala hatch can pay off big time.

Boots Allen
Boots Allen is a fly fishing guide and writer who lives with his wife and two kids in Victor, Idaho. His latest book is Finding Trout in All Conditions.