Adapted from Essential Fly Fishing by Tom Meade

An important food for trout, bass, and panfish, mayflies are born on the bottoms of streams as well as still waters. In their various stages of development, they provide a constant source of food for trout and other gamefish.

After hatching from its egg, a mayfly spends about a year beneath the water as a nymph. As it grows, the nymph continually molts, shedding its armor-plated skin for the next size up. The nymphs of some mayfly species are so minuscule that several can fit on one of your fingernails.

Others are as long as the distance from one of your knuckles to the next. Most mayfly nymphs are camouflaged, resembling the color of their environment, usually dull brown, olive, or copper. Immediately after molting, many mayfly nymphs look milky. Some are excellent swimmers, but others are not, and they get caught up in the current.

A mayfly nymph

To learn what kind of mayfly nymphs are in the water, look at rocks from the bottom or use a fly fisher's fine-mesh net to catch nymphs living in the gravel.

To select an artificial fly that simulates the most prevalent nymphs you find, first match the size and shape of the real nymphs. Then select a similar color.

Go Deep

In flowing water, the current catches nymphs and washes them down to waiting fish. To simulate a drifting nymph, cast your artificial fly so it hits the water above a spot where you suspect a fish to be hiding. Cast it far enough above the spot so it has time to sink to the fish's level. If the current is quick, you may have to use a weighted fly or a sinking-tip fly line, or add weight to your leader to help your fly sink. When fish are feeding on the bottom, you must adjust the weight on your leader frequently to keep your fly near the fish.

As you gain more experience, you will discover many ways to fish an artificial nymph. In the beginning, however, position yourself up-current from the fish's hiding spot and cast the nymph across and slightly down the current.

Sometimes, as the line swings in the water to straighten itself in the current, it makes the nymph look as though it is swimming to the surface. If a fish senses that the nymph is going to get away, the predator may attack.

If you can see a fish feeding beneath the surface, you can animate your fly to stimulate the same response: Cast your nymph up-current of the fish and allow it to drift right to the fish. Then, just as your fly is about to reach the fish, lift your rod and fly line to make the fly rise and appear as though it is going to escape.

Remember: If something looks edible and appears to be fleeing, a predator is likely to attack it.