Interesting Byron,

Some points you make I can address.

Insect that fully emerges sub surface, yellow may dun. The adult appears fully formed on the surface and almost immediately takes to the wing. This behaviour makes it one of the hardest insects to imitate. It hatches about now, and I've had some very frustrating times trying to find an imitation that works.

Insects that are blown onto the water and become "awash" In a few days the hawthorn and heather flies will begin to appear (if they haven't already) Last year I had a couple of hours on L. Lannsaidh in my float tube. I was being hit by heather flies being blown onto the water, something of a clue as to what is going on. I set up three imitations of these on my leader. The top fly being a deer hair dry the other two wets. No fish came to the dry. Twenty three fell to the wets.

Similarly, on the R. Ribble one evening. There was a large mixed hatch going on in the first pool I came to had rises everywhere. I couldn't catch. I walked upstream to find a huge spinner fall 100 yards upstream. Walked back to the first pool and put a spinner over the fish. Then I realised these were not rising, but bulging fish. They wouldn't come to the dry spinner. Sink it, and it was fish after fish.

I know both those are anecdotal evidence, but if the fish never saw these flies sub surface, why would they prefer the artificial presented in that way?

There are examples of flies that evolved into other flies that show us something relevant. I'm thinking of the likes of William's Favourite, add a tail of GP tippet and you have the Black Pennel, further add a wing and you have the Blae and Black. All flies you will find in my fly box. Some days the fish will take the William's Favourite other times the Black Pennel, still other times the Blae and Black is preferred. If the wing is a mistake why does adding it on some days mean you catch, when without it you don't? It must be adding something to the pattern.

Add to that the places where these patterns developed are not the richest of habitats for fish. Therefore, a lot of the patterns are based on attraction rather than imitation, and many times somewhere in between. It is perhaps a hard thing to say that they are a result of a mistake in understanding insect behaviour. Rather it seems that the mistake, if there is one, is in understanding what these flies are intended for, and how they work.

Good point there Byron, got me scratching me 'ed!

Cheers,
A.