What is a Stonefly? Know Your Fly Fishing Bug.

What is a Stonefly? 
Stonefly hatches are the big talk on western rivers, and the blanket hatches of rivers like the Blackfoot are legendary. Big, awkward adults make for big meals for trout. Their appearance on the river lets us start tossing the big foam and feathers around getting top eats on clumsy casts, size 6 hooks and rubber legs.  The big hatches are all anticipation and excitement, though there are plenty of minor hatches that are still crucial to fish diets. With more than 3,000 species of this worldwide mesozoic-era holdover, knowing the typical life cycle of the entire order will broaden your knowledge, and get you into more fish.

Plecoptera means, “braided wing”.
Which aptly describes their intricate wing patterns,
and piss-poor flying design.
3,000 species sounds like a lot to swallow, and it is. As fly anglers, we focus on the few larger species dependent on the region that we fish. In western Montana, this typically means hatches like the golden stonefly, the salmon fly, the yellow sally, and skwala. These big bugs are easy to find on the river, and trout key in on the hatches almost exclusively making for great fishing. The salmon fly hatches of western Montana rivers are prime examples of what makes plecoptera unique. The bugs are extremely geographically isolated, which makes identifying the specimens you find on the streamed and banks easy. The bright colors and segmentation of an adult golden stone are hard to miss, and easy to replicate at the tying bench. And their presence is a strong indicator of clean, lovely water quality. Perfect for growing big trout.
Worst hide and seek player ever. Bright colors and a distinctive body shape
make the stonefly family unmistakable trout snacks.

Lucky for us fly fishermen, stonefly hatch cycles are similar. Though they are aquatic insects and spend a good deal of their life cycle underwater, their hatch is considered to be terrestrial in nature. Stonefly nymphs develop on the bottom of the stream bed, then crawl out of the water onto rocks, sticks, and trees to shed their exoskeletons and emerge as adults. These discarded shells on shorelines are the telltale sign of the stonefly, and their imitations can be tied on and fished anywhere that you see them. Once hatched, stoneflies can live up to a month as eating, mating and providing great fishing at all stages of a hatch. Adults flutter and dip on awkward wings, often falling into the drink where trout lurk.  Spent adults fall wings spread into the water, females dip and dive to leave their eggs in the current.

Mating, and the females returning to the water to lay their eggs are of the utmost importance to us as anglers, but lets not get ahead of ourselves. The nymphal stage of a stoneflies life is a long one, and at no time in a river where stoneflies are present are there not stonefly nymphs developing and crawling around. Stoneflies can take from one to four years to develop, and the nymphs resemble wingless adults. Some have external gills that they lose during their hatch to adulthood.They crawl along the bottom, and can be rooted by feeding trout or knocked into the drift. They are excellent crawlers, and turbid moving water, rocky stream beds and runoff strengths mean a hard life for these nymphs. Crawling to shore and joining in the mating sounds like a good idea, and their annual migration is as integral a part of a fish’s diet as any other hatch. Prior to the hatch, these migrations have the trout eating.

Perhaps the most important part of the hatch, and the stage that most often produces the kind of fishing that we dream about is the return of the ovipositing female. Their awkward wings and prominent egg sacs flitter and flub around rivers and induce massive surface strikes. High riding patterns best imitate this stage, but just as important are low-riding dries as well that imitate the spent female post egg-laying.

Though the behavior, size/colors and timelines are different for all the bugs in the Plecoptera order, their defining characteristics of a clinging, crawling nymph and the award-flying adults, and their presence at all times of the year make stonefly knowledge incredibly useful for the fly fisherman. Two stages, adult and nymph, and behavioral drift that makes them migrate en masse when the right triggers are present. That means good eating for the trout, and better fishing for us.


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