“That’s a rather hard question to decide,” remarked Cecil. “Trout are particular creatures. One can never tell at what they will strike. Some days they will strike at flies similar to those you see flying over the water. That is, if white flies are flying low over the water, use an artificial white fly. However, that rule doesn’t always hold good. I have been fishing when there were millions of live white flies all over the water and the trout would not even rise for the one on my line, but when I put a dark one on, I caught all kinds of fish.”