(photo by Thomas Ames, Jr.)
The Stonefly nymph is more valuable to the fly fisher than the Dry version. Any stimulator/small muddler type will get the job done imitating the egg laying adult. The nymph is one of those aquatic insects that hatches not by rising through the water column but by climbing rocks that protrude above the waters surface or rocks along the shoreline just like damsel flies, many caddis and Isonychia nymphs. This environment is characterized by riffles. Fish the riffles and pocket water in late May and June by dead drifting this fly on a short leash!!
I've featured some stones in the past but my favorites always fall back on a larger nymph that has a yellow/brown cast to it. No need to go nuts with hackle and other things when building stones and I've found that good old ostrich works well imitating gills and legs.
Hook - size 10 nymph hook with some weight added.
Tail - some partridge fibers
Body - I use a synthetic yellow dubbing with some sparkle built into the fibers. Synthetic holds up well to rocks and trout
Gills - light brown ostrich palmered around the full body or by the thorax. I prefer the thorax style.
Wing Pad - I've used everything from duck quill, turkey quill, bunches of pheasant tail fibers and so on. The one above has a pad of Thin Skin which also works (golden oak is the color of the thin skin)
Added Feature - Run a brown sharpee down the back of this fly and you'll have created much of the color scheme of this insect.
For those without access to a tailwater Winter becomes the fly tying season so build an inventory of stones for this Spring.