Stoneflies are not as important to the fly fisherman as are the mayflies, caddisflies or midges. However, the giant "salmonfly" hatch can provide some exciting fishing opportunities. None the less, it is a good idea to carry a few stonefly imitations in the fly box as you do need to be prepared when fish are feeding on stoneflies. To reduce the number flies in your box, I would suggest that you carry a few suggestive patterns in various sizes and colors.
Stoneflies come in a wide range of sizes, perhaps the widest range of sizes of any aquatic insect. Nymphs and adults can range from over 2" (50 mm) to as small as ¼" (6 mm). Hook sizes can range from #8 to a #4. The most common range is #10 1XL to a #6 3XL.
Stoneflies have an incomplete life cycle - egg, nymph and adult. The length of the life cycle can depend upon the family or species. The smaller stoneflies usually have a shorter life cycle of one year. The larger stoneflies may have a life cycle that can last up to four years. The majority of the cycle is spent in the nymphal stage. As the nymphs prepare to emerge, they migrate to the shore and crawl out on a rock, twig or foliage before completing the transformation from nymph to adult. The nymph is especially vulnerable to be eaten by fish at this time. Adults mate on the shore with females returning to the water to lay eggs. Some species fly above the water dropping eggs into the water, other species dance above the water dipping their tails into the water to loosen eggs, yet other species dive into the water releasing their eggs on the bottom. Adults are most available to fish in the egg laying stage.
Because of their primitive gill structures, stoneflies favor flowing water. They have a preference for cool streams and spring waters. Some species can be found in lakes - usually well-oxygenated high mountain lakes.
Because of their similar behaviors, stoneflies can be divided into five groups based upon size and color differences. This breakdown can be useful in simplifying fly selection for adults and nymphs.- Up -
Nymphs - A stonefly nymph is tied much like a mayfly nymph. The stonefly nymph has two tails which are usually represented by goose biots. The body differs from a mayfly in that the stonefly gills are located under the area on or about the thorax at the base of the legs. The wing pad can be represented by various materials to include turkey tail barbs, pheasant barbs, thin skin, etc. The body and thorax areas are about equal in length. The stonefly has three pairs of legs - three on each side.
Adult - Stone fly adults most prominent feature is probably the wings. At rest the wings lay flat against the body. In flight stoneflies are clumsy fliers with wings that are prominent. A good general pattern to represent a stonefly is the Stimulator.