The variance in nymphs is not nearly as great as in the duns. None of us know what the fish actually sees but through the years I think we come to individual conclusions about what is important , mine are based on my own observations and have many factors including water speed and broken light and color variation at depth.Fishing dries to clear flat pools of pressured fish ( Upper D) has little to do with nymphing fast runs at 3' to 4' and the need for an impulsive reaction for survival found on lesser waters. Even Old Dave's imitations are a generalization of form over reality, light and dark , small and large, mayflies (epeorus, epehemerella, etc.) are just not that different , which is not to say that you don't try to match certain characteristics but you pick the ones that you think matter. I don't use other people's patterns too much anymore, it's like my music, I'd rather play my own , and I definately know what bugs are present in the streams and rivers I frequent. That's enough out of me.
