The Life cycle of a mayfly
Mayflies are a vital part of a trout's diet and hence are of great importance to fishermen. All cycles of the mayfly are important to the fly fishermen who should be armed with patterns representing the nymph, the emerger, the dun and the spinner.
The mayfly starts out as a nymph. It emerges into a dun. When its lifecycle ends and it is spent it becomes a spinner. The nymphal stage is the largest part of the trout's diet. Nymphs take on one of 4 characteristics which are important to know. They are either, crawlers, burrowers, clingers or swimmers.
The crawlers have the strongest representation in a trout's diet and provide the best fishing opportunities. Essentially, the crawlers are found in the softer riffles and runs. When they are dislodged from the surface and drift or tumble in the current they become vulnerable to the waiting trout. They live on the bottom either under rocks or gravel and are prone to being dislodged by ice moving through the water or any other thing which disturbs their cover to reveal them. Because they cannot swim, they will drift helplessly until they regain a footing.
Clingers like the faster moving water. They have evolved into flat shapes to reduce resistance to the flowing water. They have strong clinging ability hence they are less likely to be found freely drifting in the current as available food. Some have developed a suction ability to assist in clinging to surfaces.
Burrowers are found in silt and soft bottomed areas. They will only become generally available to the fish when they move out of their environment to begin the emerging stage. Their availability to the feeding fish is the most short-lived because of their natural environment as a nymph.
The swimmers live in the water freely and are strong swimmers able to control themselves better than the others in a moving water. These nymphs will rise to the surface to emerge and therefore are best fished on the swing to emulate this rising during the emerging stage.
The key to fishing nymphs successfully therefore is to understand how the nymph you want to emulate exists in the water, assess how the nymph will become available to the trout and whether it is available all year or only in certain circumstances. Furthermore, as the nymphs will be available to the fish prior to emergence, good nymph fishing is not indicated by trout taking flies off the surface. Nymph fishing can be good for hours before the hatch of the duns occurs. Fishing nymphs with this in mind extends the days productive fishing.
When the nymph begins to emerge it becomes most vulnerable to the fish regardless of type. First, the dun is trying to emerge from its shuck and can become trapped and/or exhausted and never complete the process. Hence the development of cripple patterns. In any case, as the dun is removing itself from its shuck it will be subject to the prevailing current and conditions and unable to swim or fly away until the emergence process has satisfactorily completed. When the fish are seen to be rising, take care to determine whether they are taking emergers or duns off the water. Often the angler will change to the dun too early and miss many fish which remain keyed in on the emergers ignoring the duns floating by.
Upon emergence, the wings have to dry. Again if the weather is cloudy or moist and the wings take longer to dry, the dun will be available for a longer period on the water.
Finally when the dun has completed its reproductive cycle and becomes exhausted it will fall onto the water spent. This is commonly referred to as the spinner fall. In our area this happens a little in the morning but mainly in the evening. The spinner is exhausted with one or two wings laying prone on the surface. The trout take them by gently sipping the immobile mayfly from the surface. Offering no resistance, the trout do not have to expend much energy in feeding on them.