There is not a time of year when you can't use stonefly nymphs to catch trout, panfish and even bass. Stonefly nymphs may live as long as three years in the water before they hatch into winged adults. This means that at any given time there are stonefly nymphs present in streams, lakes and ponds.
This imitation is one of the most realistic I've seen. This is called a "woven fly". These flies, believe it or not, have been hand tied, not made from rubber or plastic with a mold.
Pro tied on sticky sharp chemically sharpened Japanese Dai-Riki hooks. They are non-weighted, and very durable.