This is an article from the NEC/FFF newsletter, Backcasts. I thought I would share it with the blogosphere as well.
MATERIALS THAT MAKE FLIES LOOK LIKE FOOD:
HOW TO BRING OUT THE PREDATOR IN YOUR FISH
In the August/September issue of Backcasts I explored what properties of the fly make it look like a good meal for the fish. As I said before, the fly must look like a food source in color, shape, silhouette and texture. The eyes on the fly are also an important feature in making the fish attracted to the fly.
At this point I will also add the concept of size to our equation. This is a materials issue in terms of choosing the most appropriate hook for the job. The hook must put the fly into the proper size range to make it look like a normal food. Hooks come in different shapes and styles. Different types of bends and shank shapes impart different looks on a fly. One must pick the proper hook for the fly to be tyed. Does your fly look better on a natural 3-extra long curved hook, standard nymph hook or a scud hook? As an example I offer the idea that you may want to tye a pheasant tail nymph on a scud hook instead of a nymph hook. The scud hook actually gives the fly body a curvature that is more like the natural food. Just because a recipe asks you to use a certain size and model hook does not mean that that is the only hook that will make an attractive fly.
Hands down, I say prismatic eyes are the best eye on any fly. I am particularly fond of the domed prismatic eyes. The eye actually is a type of prism that reflects and refracts light. The best solution to the question of which eyes to use is a “no-brainer.” Other types of eyes leave the fly looking flat and lifeless.
Color is another issue that is easy to address. Our fly tying materials, both natural and synthetic, are available in a cornucopia of colors. If fish are feeding on tan caddis, it stands to reason that I want to tye a tan caddis imitation. It is really hard to justify any other color. Tye your flies in colors that will match the hatch not just the recipe.
Now, without going through a treatise on every fly tying material, let's look, in general terms, at texture. There are a number of materials to use which add scale-like effects to a bait fish imitation. Try lateral scale or crystal flash to add the crinkly look of scales. Shine and shimmer are also found in the vast array of metallic and mylar tinsels that can be found on the walls of any decent fly shop. Synthetic hair has come a long way since the time when we just had craft fur. Check out what is available from a number of manufacturers. It is also important to determine if you want a stiffer or more limp material as this will effect different types of movement and the silhouette when the fly glides through the water. I suggest you use good judgment and follow your intuition about what looks edible and good (to you and the fish) as the recipe may not necessarily be recommending the best available material in this day and age.
Finally I must comment on the feathers that Mother Nature has given us. By way of example I will bring up mallard. When tying a slip-style wing on a wet fly, would you want to use the reflective and iridescent blue feather on the mallard wing, or the plainer-looking gray ones? Ask yourself which would make a more enticing fly.