It seems right for Mayflies to be featured as the critter of the month for May. After all, legend has it they acquired their common name thousands of years ago, due to their habit of ‘hatching’ as adults during the month of May. Of course, this would have been observed in one of two species from one part of the northern hemisphere, but the name has stuck, and now over 3000 species have been described the world over, and mayfly hatches can be observed at any time of the year.
Mayflies are of the order Ephemeroptera and are famous for living for only one day. Of course, this again is true of the adult phase of some species – others may last several days, or weeks. Together with stoneflies, caddis and midges, mayflies form among the most important aquatic insect species for river ecology and food for freshwater fish – especially trout. Adding to that, there have probably been more mayfly imitations tied by fly tyers the world over than any other insect species over the past few hundred years.
While the various mayfly species all have slightly different life cycles, there are three main stages of the life cycle common to all of them that interests both the fish and fly angler the most. 1) The nymph, 2) The dun and, 3) the spinner.
The nymph phase is the part of a mayfly’s lifecycle spent underwater from its hatching from an egg to its emergence as a terrestrial adult. The insect will grow and transform during this period, but they make great fish food at any stage and can be imitated reasonably easily by fly tyers. The pheasant-tail nymph is one of the world’s most popular flies and no self-respecting trout angler would think of going trout fishing without a few of these in their fly box. Along with countless other patterns – they make a great mayfly nymph imitation and I’m sure millions of trout have been caught on them over the years.
When the time is right, mayfly nymphs will make their way to the water’s surface to emerge as an adult. The first stage of the adult mayfly is known as the sub-imago, or more commonly, the ‘dun’. Duns are usually dull coloured, popping out from the nymphal shuck and flying awkwardly to rocks or streamside vegetation where, after a short period of time- usually a few hours – they shed their skin for the final time to emerge as the imago, or ‘spinner’.
Spinners are the final life phase of the mayfly. They get their common name for looking like they are spinning as they work their wings to stay airborne usually in great swarms in low afternoon light. During this time, they are looking for a mate, before the females lay eggs in the river, to start the cycle over again, then die shortly after where they can be seen splayed out flat on the water surface.
At all times during their life cycle, mayflies are an important food source for many animals – especially freshwater fish. Tying mayfly imitations and fishing a ‘hatch’ is one of the great moments in trout fishing and something not to be missed. See the video below to witness the fascinating life cycle of the mayfly.
Video: NatGeo Wild
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