Artificial flies are designed to imitate the various stages of aquatic and terrestrial insects, or small baitfish, which are natural food sources for fish. Understanding the four main categories of flies is essential for fly fishing success.

1. Dry Flies

Dry flies are designed to float on the surface of the water, mimicking an adult insect (imago) resting or drifting. They are typically tied with buoyant materials like deer hair or hackle.

• When to use: When fish are actively feeding on the surface, or "hatching" insects are visible.
• Key characteristic: They float.
• Example imitations: Mayfly, Caddisfly, and Stonefly adults.

2. Nymphs

Nymphs are designed to sink and imitate the immature (larval or pupal) stages of aquatic insects. These are often fished near the bottom of the water where fish do most of their feeding.

• When to use: Year-round, as the majority of a fish's diet consists of sub-surface food.
• Key characteristic: They sink and often have a weighted head or body.
• Example imitations: Mayfly nymphs, Caddis larvae, and Stonefly nymphs.

3. Streamers

Streamers are generally larger flies designed to imitate small baitfish, aquatic worms, or leeches. They are fished by being stripped or moved through the water to mimic the swimming action of prey.

• When to use: To target larger, predatory fish, or when no surface feeding is occurring.
• Key characteristic: Large size, often tied with long, flowing materials like marabou.
• Example imitations: Minnows, sculpins, and crayfish.

4. Wet Flies and Emergers

Wet flies and emergers are tied to sink just below the water's surface. Wet flies typically imitate drowned insects or ascending nymphs, while emergers specifically mimic insects as they rise from the streambed to the surface to hatch.

Fly Type	Position in Water Column	Primary Food Stage Imitated
Wet Flies	Sub-surface (sinking)	Drowned or descending insects
Emergers	In or just below the surface film	Insects rising to hatch
Dry Flies	On the surface	Adult insects