As a general rule, cock hackles were / are used on dry flies and hen hackles on wet (subsurface) flies.
One major exception to this is on palmered loch flies where cock hackles are used for the body hackle. Non genetic hen hackles are not long enough to palmer a standard size loch style fly.
If you palmer a loch style fly with a genetic hen hackle (longer than a non genetic) the effect can be very nice but as a general rule most palmered flies use a cock hackle for the body hackle. I do tie a few palmered loch flies with Metz hen hackles.
I prefer to add a slightly longer hen hackle in front of the body hackle to give more movement, the cock hackle also prevents the front hen hackle from collapsing along the body of the fly by supporting the hen hackle fibres.
Some people prefer a cock hackle in front of the body hackle, the best thing to do is to knock up a few of each and fish them to which style you prefer.
River spiders tied to fish subsurface just look wrong with a cock hackle, the softer hen hackle folds back and "kicks" much more than a cock hackle making the pattern look more alive.
Other people may have a different view, this is just what I prefer.
The great thing about tying your own flies is that you can change any pattern to try a different style, the fly police may object but it's YOUR fly.
Unless you are tying to sell to customers, tie the fly the way you like them.
By the way, all the reports from several shops I buy from seem to indicate that genetic cpes are set to rise in price soon by a significant amount, (price of food for the birds and fuel costs for heating the sheds) buy the capes you think you will use now to beat the price rise.
Kev.
