Western Stoneflies
Two summers ago I received a phone call from my fishing partner. It was the first week of June, and according to my buddy, Salmonflies (Pteronarcys californica) were hatching on the Colorado River near Parshall.
That phone call was a call to arms. It meant we had to drop everything and head straight to the river. Not tomorrow or the next day—right now.
Seasoned anglers know that stonefly hatches are feast or famine. Timing is everything. Hit the hatch perfectly, and you think you’re the consummate angler. Miss it, and it’s one of the biggest disappointments of the year.
Stonefly hatches provide some of the best opportunities to find large trout feeding voraciously on aquatic insects. In the case of Salmonflies, Golden Stones, and Skwalas, the insects are also large, tempting trout to the surface or shoreline areas to prey on nymphs.
Order Plecoptera
Stoneflies are of the order Plecoptera, which means folded wings. (“Pleco” means folded and “ptera” means wings.) The order Plecoptera, commonly called stoneflies, has an incredible diversity of species—nearly 600 in North America alone. It’s easy to underestimate their importance because, as the common name implies, stonefly nymphs mostly hide among rocks on the stream bottom.
Most stonefly species thrive in similar habitats. They have specialized gill structures that limit their living quarters to cold, unpolluted, highly oxygenated trout streams. On most Western drainages, it’s rare to flip over a rock or log and not find a stonefly or two crawling under it. A fast-water seine sample also demonstrates their prolific nature.
Stoneflies pass through an incomplete metamorphosis. Unlike caddis and midges, they do not have a pupal stage in their life cycle. The durations between their life phases—egg, nymph, and adult—depend on the species and on water temperatures.
Smaller species, such as Early Winter Stoneflies, Yellow Sallies, and Skwalas, typically have a one-year lifespan. Larger species, such as Golden Stoneflies and Salmonflies, generally live from three to four years.
Nymphs
As a result of the multiyear life cycles of the larger stonefly species, several different year classes live in the stream at any given time, and stonefly nymphs remain plentiful year-round, even after the adults have emerged. Since the trout see and eat nymphs all year, Western anglers should be prepared to fish them at all times—not just near peak hatch periods.
Don’t rule out fishing stonefly nymphs in January, basing your decision simply on the time of year, or because you don’t see any. Throughout the winter months, tumbling ice chunks frequently dislodge stonefly nymphs from the substrate, creating a feeding frenzy.
Stonefly nymphs have forked tails, segmented abdomens, branched gills, three sturdy pairs of double-clawed legs, pronounced wing pads, prominent eyes, and slender antennae.
During emergence, stoneflies migrate toward the river’s edge and crawl from the water onto streamside rocks, willows, grass, and trees to hatch into adults. You’ll see evidence of this process in the form of their empty exoskeletons clinging to bridge abutments and boulders along the river.
Because the hatch occurs on land, stonefly nymphs transitioning to adults (“emergers”) are not available to trout during the emerging process. But the heavy concentration of nymphs along the streambanks during the migrating process increases their availability at certain times of the year. Nymphing along the river’s edge is highly productive during these migration periods.
Adults
Not surprisingly, adult stoneflies look similar to the nymphs, with the exception of the two pairs of veined, folded wings—two forewings and two hind wings—over their backs.
Unlike mayflies and caddisflies, stoneflies do not produce mating swarms or spinner falls. Instead, they mate on land. Male and female stoneflies locate one another by drumming or tapping their abdomens on branches, tree trunks, and rocks. The male initiates one rhythmic pattern, which is subsequently answered by a female. Each species has its own unique drumming pattern.
Adult stoneflies consume fluid foods, and as a result sometimes live between one and three weeks before they find a mate. After they mate successfully, females fly over the water and drag their abdomens on the surface to deposit their eggs, but other than that, stoneflies rarely fly. They crawl to find and meet their mates.
The good news is that stoneflies are clumsy. They are easily dislodged by wind, and once airborne, they are poor fliers. They often end up in the water, where they flutter, creep, and clamber toward the shore, or drift aimlessly. If they aren’t eaten, they often drown and are washed downstream to be eaten submerged, as nymphs would.
Copyright © 2012 Intermedia Outdoors
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