When a hatch comes off, the instinct is to dig for the perfect color. Wrong order. Trout key on three things, and they matter in this exact priority:
- Size first. Get this closest. A fly one hook size too big looks fake even in the right color. Catch a bug off the water or off your sleeve and lay your fly next to it - they should be the same length.
- Shape (silhouette) second. Match the bug family. A mayfly rides the surface with upright sail-like wings. A caddis holds wings tent-shaped over its back and skitters. A midge is tiny and slim. Pick a pattern that throws the same outline.
- Color last. It is the most forgiving. Roughly right is fine.
A fly the right size and shape in the wrong shade out-fishes a perfect-color fly in the wrong size, every time.
Now the part most people miss: match the life stage fish are eating, which is often not the adult riding on top. Emergers stuck in the surface-film usually out-fish the dun. And a spinner fall - dead, spent-wing bugs flat on the film - looks like nothing is happening while fish quietly gorge.
When nothing is hatching, stop forcing a match. Tie on an attractor or a searching nymph and cover water.
Before you go, check the FishCast hatch chart on the water report for your date. It tells you what should be on so you can stock the right sizes before you are standing in the river guessing.