In the soft, minor tones of a Michigan trout stream the picture at left shows the delicate beauty of a Mayfly at the instant of its birth. A few seconds ago the Mayfly was a brown, grublike thing, struggling upward from the silt of the stream bed. Now, full-born, it rests on the surface, drying its fragile and richly veined wings. From this moment the Mayfly's life will be brief and poetic; it may last less than a second, never as much as a week, and for as long as it lives it will be devoted entirely to the art of love. At any time, however, this ephemeral creature may disappear into the stomach of a fish, for the trout do not regard the insects as either romantic or poetic, but merely appetizing.
Mayflies are to trout as trout are to fly-fishermen. Fifty species of North American Mayflies provide so substantial a portion of the food of U.S. trout that they are of primary concern to fishermen. One of the largest and most fascinating of the 50 is Hexagenia limbata—the fly shown on the opposite page—a giant among its kind that appears nocturnally in fantastic numbers on the big, cold trout rivers threading the Michigan plains south of the Straits of Mackinac.
When Mayflies make an appearance in any strength on a trout stream, fly-fishermen stretch a technical point and call it a hatch. The mating flight of Hexagenia limbata puts so many insects on the water so fast that Michigan woodsmen call it a blanket hatch. A trout fisherman exposed to one for the first time can scarcely believe what is happening. The fish go wild.
One June evening a mating flight of good-size Mayflies—gray drakes—was overhead in the dusk on Michigan's Au Sable River. The trout were feeding well on the dropping females when I noticed the abrupt influx of a much larger fly. It seemed to come from nowhere. The surface would be bare, and in the next instant it would hold a big, grayish Mayfly with large wings erect like a sail.
One floated toward me. As I bent to look, a trout flashed white in the water, taking the fly so near that drops from the rise struck my face. I had had time, however, to identify the fly as Hexagenia limbata. In the next few moments the air around me was filled with a blizzard of these majestic insects, and the surface of the pool was roiled and churned as the trout erupted in a frenzy of feeding.
This was my first experience of the manna that big nocturnal Mayflies bring to heavily fished public water. It was one of the rare times I have seen Hexagenia limbata in enough natural light to observe the abandon with which otherwise skittish trout move in to feed.
In the full darkness, when king-size Mayflies normally appear, the fishing is blind, carried on in an eerie world where your awareness is limited to what you can hear and feel.
At first you strike at sound alone and are jolted by a sensation familiar to the batter who swings and misses. In time, hearing, touch and rhythm compensate and you no longer confuse the light but noisy rise of a one-pound rainbow with the quieter strike of a heavy, wary brown trout weaned of his natural suspicion by the cover of darkness.
This phenomenon of the blanket hatch, with its rich dividends to the angler, is not limited to midwestern waters. At least two well-known species occur as far east as the streams of New York and Pennsylvania: they are Ephemerella guttulata (known as shad flies and coffin flies) and Hexagenia recurvata (the brown drakes). These normally appear earlier in the season on more southerly streams than Hexagenia limbata, are neither quite so large nor so numerous and are prevalent in late evening rather than in full night. Other than in size, numbers and nocturnal nature of its appearance, Hexagenia limbata is similar to all other Mayflies.
Hexagenia limbata, measuring an inch and a quarter in the body, with two-inch tails, has the same tapered, arching form, the same handsome triangular-shaped wing as the little Caenis fly, a bare one-eighth of an inch long. Characteristics of the order include two pairs of wings (although some tiny species have but one pair) and a life cycle of three stages—egg, nymph and winged insect—with the eggs and nymphs maturing in water. It is this last characteristic that has elevated Hexagenia limbata in the minds of fishermen, because the water they prefer is the same clear, cold, pollution-free water trout prefer. In such water Mayflies often are the dominant insect. At all stages, from its first weak movements as a tiny subsurface nymph until it makes its momentary appearance on the surface as a winged adult, the Mayfly is fiercely hunted by trout.