http://www.flyline.com/1f_fish_t/myths/myths.htm
The article linked above by Truckee, CA's Ralph Cutter is a great article by one of my favorite flyfishing/tying researchers.
Techniques: Flyfishing Myths, Legends, Lies and Other Trout Fishing Facts published in California Fly Fisher magazine
In additional to a lot of other interesting stuff, here's some excerpts related to fly tying. Comments?
1. Eyes on streamers provoke strikes. It is widely held that predatory fish key in on and attack the eyes of bait fish. As "proof" many anglers cite the presence of ocelli or false eyes near the tail of some fish. They contend the predator will target these eyes and the attack will be directed toward the tail.
Studies around the world with numerous species of fish show that that predatory fish do not aim for the eyes. In every instance the mid section of the prey was targeted. The size, shape, location, presence or lack of the eyes (or ocelli) in no way altered the point of the attack.
Researchers have found that very often a predatory fish will not attack if the eyes are visible. Time after time bass, pike and barracuda have been observed rushing past available bait to take a fish with it's back turned. It seems predators have learned they can get the jump on their prey when it's not looking.
Ocelli located near the tail of bait fish may give the impression it is "looking" when its back is turned and avoid being attacked. For the same reason eyes on a streamer may actually be counter productive.
There is no doubt some flies are more effective with eyes than without. Eyes can add both physical and visual balance to a fly. The eyes may add just that certain bit of spark, brightness or contrast that makes the pattern irresistible. In certain patterns, eyes impart action and even noise to a streamer. Blanton's Whistlers and Clousser's Deep Minnows are good examples; exchange the lead eyes on a Deep Minnow with plastic eyes and the fly loses both it's jigging action and fish catching qualities.
4. You must match the color of the prey. What a crock. Trout see every color we do, plus they can see infra red and ultra violet. When we see a green caddis larvae, we are seeing an object that is absorbing all the visible wavelengths of light except blue through yellow. These colors are reflected in a blend of light that appears as green to the human eye.
What if this caddis is also reflecting ultra violet? It'll still look green to us because we can't see UV. To the trout who can see into the ultra violet spectrum, the caddis will look something far different from green.
It is well known that many patterns, such as Bob Quigley's para nymph, work better when tied in purple rather than the PMD hatch matching yellowish green. To our eyes the imitation looks nothing like the real thing, however, the infra red reflecting qualities of the purple fly are better at imitating the natural as the trout perceives it. And that's what counts.
Out of a laboratory we have no way of knowing how trout perceive a bug. Luckily, it doesn't matter. Trout don't care if the fly contains the wrong color. Blend lots of colors into your dubbing . . . as long as the right color is present , most fish selectively discriminate against the wrong colors and take the bug. Whitlock's "bright dot" flies are a perfect example of this.
8. Nymphs should be weighted. Imagine a little, nearly weightless, stonefly nymph getting swept off his rock and hurled downstream. Like a leaf in the breeze, every subtle waft of current will swing the bug upwards then spill him sideways then tumble him a few times for good measure. It is called "catastrophic drift" for a very good reason.
Now imagine a spark plug.
An unweighted nymph imitation much more closely approximates the behavior of a real nymph in the current. People are fanatics about presentation when their fly is drifting on the film but become complacent when fishing nymphs. Out of sight out of mind I guess.
Put enough split shot on your leader ( maybe two inches from the imitation) to take the nymph down, but once down, let nature take its course with your bug. I go so far as to treat my nymphs with fly floatant to increase their buoyancy.
