This is a very simple fly and it is also the most effective back lure of all. No fluorescence and no flash.
This fly catches a hell of a lot of fish, it works best mid-summer onwards on overcast days or else right before dark and beyond. It's also my number one September fly. I have no idea what it imitates, but it definitely suggests food. Fish just under the surface on a floater or else on the point with an Intermediate. I think the most important thing to stress is that it is best fished slowly.
size 10 long shank, black thread, black chenille body ribbed silver wire, tuft of black marabou wing. Why be complicated?