I truly believe the answers are, not that many; quite few; very little.
That of course doesn’t hold me back, because I really enjoy tying flies - yet, it also hurts a little more sticking an Oliver Edwardfs-style nymph in the bottom than a Pheasant Tail. And apart from the odd instance, I can’t say one is better than the other. We’ve probably all been in situations, where a fairly accurate representation of what’s on the menu makes the difference, but for me, that’s always been when they fish are feeding on the surface.
Once the feeding and fishing takes place deeper, there’s very little light for the fish to discern food from not-food. Anyone who’s taken a closer look at trout feeding subsurface know that they take all sorts of debris and stuff swimming past them and discarding again, if it’s not food.
I actually have mu doubts about whether or not trout and grayling really do become selective when they feed subsurface. Maybe someone knows better?
And Frank Sawyer caught thousands and thousands of grayling on his Killer Bug and Pheasant Tails, which in itself shows that they are probably enough in most cases.
They are both represented in the PoD and so is Oliver Edwards’ elaborate and beautiful Baetis nymph. And bottom left, a simple, all round nymph, tied with yarn, copper wire and hen hackle fibres for legs and tails (are they even necessary?).
I fish them all, not with any deep though behind and of the four, Sawyer’s Killer Bug has caught me the most fish.
Habe a great weekend!