In this Fish and Fly exclusive extract from John Bailey's Fishing Encyclopedia he talks about how to use the traditional wet fly.

"When you’re nymph fishing you are trying to imitate a real-life food item. It might not be an exact imitation but it’s a good general impression. Traditional wet fly fishing, however, is a little bit different. A traditional wet fly will try to deceive fish into thinking that it is natural but it is more an impression of life than any exact replication. But wet flies are not all the same.................."