A trout’s diet is made up mostly of aquatic and terrestrial insects. Mayflies (an aquatic insect scientifically termed Ephemeroptera) are the best known of all trout foods. They occur virtually everywhere in the world, they are prolific and, in most places, a big favorite on a trout’s menu.
Mayflies have nothing to do with the month of May. Their life cycle begins at different times of the year, depending on their type and other natural factors such as water flow and temperature. Simply stated, the beginning of their life is keyed to the life end of the female adult. The mayfly life cycle generally lasts about one year, and comes in four distinct stages: the egg, the nymph, and two adult stages; the adult sub-imago (dun stage), and adult imago (spinner stage).
Briefly, at the outset of the spinner stage, the female and males swarm together and mate midair, fertilizing the eggs. The female spinner deposits the eggs on or below the water’s surface on a lake or stream, and the eggs sink and stick to bottom structure. The spinners, both male and female, die from exhaustion. This final step concludes the mayfly’s life cycle.
These tiny eggs hatch within days and the tiny nymph is “born“. At this early stage, the nymph is too small to be trout food. As the nymph develops, it grows larger and becomes trout fare as it moves around the bottom, or as it floats or swims to the water surface for the first adult stage, the dun. This movement on the bottom or to the surface makes the nymph most vulnerable to the feeding trout. This metamorphic action is a fly fisherman’s dream come true.
Mayfly nymph imitations representing the crawling or swimming nymphs are trout-catching flies at their best. A sinking fly line, a fly line with a sinking tip, or a weighted artificial pattern are effective at this time. The nymph imitation can be weighted with lead wire wrapped on the hook shank prior to dressing the fly, or by tying the nymph with the addition of a heavy bead head for added sink ability. Even rough representation of the natural’s size, shape and color will usually be adequate.
The Pheasant Tail Nymph and the Gold-Ribbed Hare’s Ear Nymph in shades of tan to brown, light olive to dark green, and light grey to black all make excellent mayfly patterns for the fly angler’s fly box. These two patterns are my favorites.
While the dry fly fisherman has a visual response to his dry mayfly being taken on the water’s surface, the practiced nymph fisherman will usually land more trout. The nymph fisherman cannot always see the fly below the surface. He is looking for the flash of the bright-colored trout as the fish “takes” the artificial, for any bulge on the water’s surface, for a twitch of the fly line or leader, or for the tracking line to abruptly stop in the middle of the drift. All of these indications can represent the trout’s presence and should be a signal to “set” the hook.
If you have not considered fly fishing with a mayfly nymph, I urge you to give it a try. Yes, there is a learning curve, but the results will make you a more productive fly fisherman.
FLYDAHO 