Imitaitons of stonefly nymphs could very well be called the ”year-a-round-fly”. The nymphs are active all year round and fish are not late to take advantage of this and provide themselfs with a ”snack” rich in protein. Overlooked by many anglers in Northern Europe, but well known in the states for example. But no matter were you fish, imitations of stonefly nymphs will catch fish.
Stonefly nymphs do not swin to the surface to hatch, like many mayfly species. Instead they either crawl up on the shoreline to hatch or use plants, logs or stones to climb up to the surface. Due to there lack of good swimming capablities, the stick to the bottom most of there life. However, from time to time, they will drift downstream by accident or in order to find new habitats. During these drifts they become an easy target to fish species like brown trout.
Remember to fish you imitaitons close to the bottom.