Adapted from Essential Fly Fishing by Tom Meade

Find a clean, bubbly stream and you probably will find stoneflies, a staple in the diet of trout in waters bristling with oxygen.

Fish gobble up adult stoneflies, also called salmon flies, when the insects emerge from the water. Trout probably eat more nymphs than adults, however, because the immature insects are more abundant most of the time. The nymphs range in size from less than a half-inch long to the giant stoneflies of the American West, which are as long as three inches. They have two tails.

Stonefly nymphs emerge from the water throughout the year, usually crawling onto an exposed boulder or the shore. The adult stonefly breaks out of the nymph's armor, leaving its former shell behind. On many western rivers, stonefly husks cover entire boulders and bridge abutments where the nymphs crawled out.

A stonefly

On some western streams, stoneflies are the trout's principal food source. When the adults are not hatching, you will need a strong leader to fish large, weighted imitation nymphs. To catch fish, animate the fly so it looks like a big bug swimming beneath the water: Cast it across the current, and as the flow sweeps it down, twitch the fly with your line hand, pulling in small lengths of fly line.

The wings of artificial stonefly adults sweep back over buoyant bodies-like the real insect.

In the East, where anglers sometimes mistake small stoneflies for caddisflies, artificial caddisflies often will fool fish feeding on little stoneflies.

On some western streams, so many real stoneflies emerge at once that your artificial fly can get lost in the crowd. When you find yourself in such a massive hatch, find a fish that is feeding steadily on the surface and cast your fly to make it alight just up-current from the fish, and let it float to the trout without any unnatural movement, or drag.

If you are convinced that your fly is the same size, shape, and color as those of real stoneflies on the water but the fish continue to refuse it, try this: Just before the fly floats over the fish, twitch it slightly. Sometimes, animating a floating fly triggers a predatory fish to attack.