Mayfly Life Cycle & How to Fish Mayfly Patterns

Mayfly – The Life Cycle & How to Fish Mayfly Patterns


Mayflies are one of the most elegant of the species in the world of fly fishing. They are also one of the trout’s most important food. Learning more about mayflies, mayfly life cycle, appearance and behavior becomes crucial when fishing mayfly patterns. Here, we will try to cover the main life phases of this interesting insect and its intertwined connection to its big predator – the Trout.

Order: Ephemeroptera

Mayflies (also known as shadflies), belong to aquatic insects. They are primitive species, the oldest of the winged insects and can be dated back to the prehistoric ages. Mayflies go through incomplete metamorphosis, going from egg to nymph to adult, and lacking an intermediate pupal stage. The mayfly nymph, in essence, is a larva which, unlike a typical insect larva, already resembles an adult’s form. (Complete metamorphosis in insect world includes four stages: eggs, larva, pupa and adult.) On the other hand, mayflies are unique as being the only insect to have two winged adult life stages – the sexually immature – subimago and the reproductive, mature – imago.

Mayfly Life Cycle

Molting: Nymph to Emerger

Molting (moulting) or emerging of nymphs happens when the water is warmer (in spring and fall), or during mornings or evenings in the summer time. When mayfly nymphs start molting, air and gases start collecting under their protective shell (exoskeleton), increasing their buoyancy, which pushes them up to the surface. They start fighting the upper pull forces and large percentage dies in the process, not having enough energy for the transformation. During molting, nymphs don’t breath.
They start coming out of their exoskeleton either while still subsurface, or when they float to the surface (a few species crawl to the shore to molt). Mayflies that are in the molting phase are called emergers. Their exoskeleton splits along the back and they pull themselves out and lift up their wings.

11756529116 f0e96602fa z - FrostyFlyMayfly Molting (Emerging): Emerger to Dun
Photo: flickr photo shared by sighmanb under a Creative Commons ( BY ) license

Subimago Stage: Emerger to Dun

When the exoskeleton breaks open and the adult mayfly gets released – the nymph emerges into an adult – a dun (subimago) that has dull-colored wings and breathes air. They float on the water surface and wait for their wings to fill with fluid and their veins to harden (as opposed to common presumption that they are drying their wings). During this time they are vulnerable and easily become pray to the hungry fish. Dun seeks shelter in the vegetation on the river banks. Mayfly duns live short lives before they transform again, most species only a couple of hours, but this can range anywhere from a few minutes to a couple of days. They are not such great fliers. The adult mayfly dun is sexually immature (unique in nature) and goes through another molt.

Second Molting: Dun to Spinner

Second molting of a winged adult mayfly is quite unique in the world of insects. The final transformation is from a dun to a spinner (imago) – with clear wings. As spinners, they have no digestive organs and cannot eat or drink. They only have reproductive organs. Adult spinners have short antennae and large eyes. As they do not eat or drink, their mouth is non-functional. They release a scent to attract their mates.

Mayfly Molting: Dun to Spinner - Mayfly Life Cycle & How to Fish Mayfly PatternsMayfly Molting: Dun to Spinner
Photo: Mayfly Molting by Sandy33311 on DeviantArt (license)

Mating: Spinner to Spent

Spinners, as they mate inflight, fly in big swarms and as they fly close to the water – this is called a ‘spinner fall’. After mating, the female would fly off to the vegetation to wait for eggs to fertilize. They would return to the water to descend to the surface of the water to lay eggs. Most drop the eggs while still inflight, from above the water, while others dip the back part of the abdomen to deposit them into the water. This process is exhausting. When they are finished, they simply fall to the water surface and float motionless, with their wings stretched out on the water and are now known as spent. Spinners die usually shortly after mating, usually within a couple of hours. These spinner falls usually happen in either dusk or dawn and are a great time to catch some trout rises. After mating, male spinners mostly fly off to the nearby shore where they would die. Most spent mayflies found on the water surface are females – and these insects should be imitated when tying your patterns, as males and females can differ in sizes and colors.

Deposited mayfly eggs drop to the bottom and stick to stones and vegetation, from where they would hatch into nymphs within either a few days to a couple of weeks, depending on the species. During the hatch, as mayflies mate in enormous swarms, all at the same time, for trout and birds that feed on them this comes as a feeding frenzy. For fly fisherman – a challenge in itself as getting a trout to bite into your mayfly imitation on a hook when so many other real insects are offered is no easy task. Mayfly hatching typically lasts a couple of hours and occurs in a period of few days during spring or summer, but, there are a few species that hatch in the fall.

How to Fish Mayfly Patterns

There are a few instances in mayfly life cycle when they are most vulnerable to the trout, and these are all great opportunities for a fisherman to imitate with flies, each with its specific patterns.

  1. Subsurface, when the mayfly nymphs start their journey to the surface, they are an easy target to the trout.
  2. On the surface (or subsurface) during their emerging from their exoskeleton.
  3. While they are floating on the surface as duns, getting ready to fly off.
  4. During egg drops – trout find them the most delicious while still containing eggs as their body consists of eggs mostly at this phase, plus they are super nutritious.
  5. When they fall to the water, known as spent.

Each of the above mayfly life cycle phases should be looked at separately, matched with different fly patterns and different presentations.

Fishing Mayfly Nymphs

Mayfly’s underwater life is fairly long compared to its dry stage. Typical mayfly nymph lives anywhere from few months to few years in the water, living in the protective gravel, protected by their camouflage coloring. A presence of mayfly nymphs in the water is a good indication of purity of the water – they live in clean, freshwater environments. Nymphs live under rocks or in sediments. They feed on algae, plants and leaves. Most mayfly nymph species have three tails, but there are a few with two. They grow in stages that are called instars. Each instar they shed their skin (exoskeleton) and until they reach maturity (time to emerge) they can go through many of these instars, as many as twenty. All mayfly nymphs have gills on their abdomen and one set of wing cases, which makes them distinct in the aquatic insect world.

There are four major groups of mayfly nymphs, each with its specific shape, movement and behavior: swimmers, clingers, burrowers and crawlers. Each of these groups is asking for its specific gradation in pattern and presentation of the fly.


Swimmers have weak legs but lean bodies that is streamlined for moving fast through water. They can swim very fast, even upstream, and can be found in both, very fast currents as well as slow waters, even lakes and ponds. However, their favorite habitat are moderate to slow currents with weed beds and lots of aquatic vegetation – like spring creeks. They breathe through gills located along the sides of their bodies. Their tails are fringed to enable them to swim faster. Swimmers tend to be on a smaller size, #10 down to #20. Gray drake and blue-winged olive are swimmers. One of the effective patterns to use for swimmers is Pheasant Tail. On slower currents, the best presentation with swimmers would be a delicate long cast, drag-free drifts, but an occasional light twitch to give it a short darting motion would also work. In faster waters, no action is needed.

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Mayfly swimmer nymph – ‘Small minnow mayfly, Baetis tricaudatus’, Photo by Bob Henricks
Photo: flickr photo shared by henricksrobert under a Creative Commons ( BY-SA ) license


Clingers live in fast rivers and streams and are mostly found under stones. They are rarely found in still water. Their strong legs enable them to easily cling (grip) to stones tightly. They have wide and flattened bodies which helps them fight even the strongest of currents. They breathe through gills located along the sides of their bodies. Their eyes are prominent and located on the top of their head. Clingers are found mostly under the rocks and are only available as food at the times of a hatch. You can start fishing them about one to two weeks prior to the hatch. March brown is a one of the clinger nymphs. Clingers are medium sized nymphs, from #12 to #16. A good pattern for clingers is Hare’s Ear, but a wet fly pattern would also be very effective as these nymphs emerge subsurface. As for presentation when fishing these nymphs, dead drift works the best, casting it slightly off from straight across (either up or down) and letting it drift drag-free. Letting your fly drift towards the edge of the riffle into the slower waters would be most effective.

Mayfly clinger nymph – ‘Flatheaded mayfly, Heptagenia marginalis’ - Mayfly Life Cycle & How to Fish Mayfly Patterns

Mayfly clinger nymph – ‘Flatheaded mayfly, Heptagenia marginalis’, Photo by Bob Henricks
Photo: flickr photo shared by henricksrobert under a Creative Commons ( BY-SA ) license


Burrowers live in calm, slow waters and have long bodies and short, but very strong legs with large claws which enable them to dig protective burrows in the gravel of the river bottom. They have pale, yellowish bodies and are mostly nocturnal. They breathe through gills located on the upper side of their backs. Their tails and abdomen area are fringed and feathery. Most famous burrower is ephemera. Fish can find burrowers when they come out of their hiding – at night to eat or in times of a hatch, which also happens when it’s dark – starting at late evenings. To fish burrowers, drifting along the bottom would be your best bet. Due to their size – they are a tasty meal for the trout that rarely gets passed. In size, they range from #4 to #10, most common being #8 and #10.
15438453129 4c0da23ffc z - FrostyFly

Mayfly burrower nymph – ‘Common burrower mayfly, Ephemera guttalata’, photo by Bob Henricks
Photo: flickr photo shared by henricksrobert under a Creative Commons ( BY-SA ) license


Crawlers are found in medium to fast waters, their habitat being brisk waters with rocky bottom with lots of small crevices and nooks. They have very strong bodies and legs adapted to crawling. They look like clingers and can easily be mistaken. The big difference is in the position of their eyes – they are located on the sides of the head. Their gills are located on the upper side of the abdomen. They are not great swimmers. They range in size quite a bit, from #8 to #24, but most important ones being in the range #12 to #16. Popular crawlers are green drakes and pale morning duns. An effective pattern would be Hare’s Ear. An upstream cast with a light tumbling along the bottom would be a good presentation for this fly. An indicator would be a useful tool here.15999624830 964023dccf z - FrostyFly

Mayfly crawler nymph – ‘Spiny crawler mayfly, Drunella doddsi’, photo by Bob Henricks
Photo: flickr photo shared by henricksrobert under a Creative Commons ( BY-SA ) license

Fishing Mayfly Emerger

When in the emerger phase, mayflies easily become trout’s pray. Furthermore, an emerger is always a better meal choice for a trout than a dry fly. Least effort, most calories. If you see dry flies on the surface and trout rising but not taking them in, most probably a trout is grabbing those emergers subsurface. You can tell if trout is feeding on emerger by the way they rise and what you see showing above water. If you do not see the head, and only see the dorsal fin, then a tail with a splash, it is most likely the emerger in trout’s mouth. Great mayfly emerger patterns are Soft Hackle Mayfly Emerger and CDC Mayfly Emerger. As for presentation, dry fly drag-free drifting is most effective. An occasional slight drag could produce a strike as it brings the fly close to the surface, but keep it as short as possible.

Fishing Mayfly Dun

Mayfly dun has usually three long tails (some have two). Their forewings are large, lightly-colored and transparent, covered with veins and standing upright (similar to those of a butterfly). Some species have hindwings, however, these are small in size and have no function (they are vestigial). Their bodies are long and tapered with long, slim legs. Their size ranges from #4 to #24, with most common size between #12 and #18.

Majority of mayfly species molt in the spring and early summer, while others do it at different times of the year. You could have sporadic hatches of certain species even in the late fall and early spring. These sporadic times could be even more interesting and productive for trout (and for a fisherman). During early spring and the fall, mayflies hatch in the warm hours of the day – usually midday. In the summertime, this event moves more towards the morning and late afternoon or early evenings. Usually, the warmer the weather, the shorter the hatch is – an hour or two. With cooler weather this can last a couple of hours. As mayfly duns float on the surface like little sailboats, this behavior dictates the method of presentation of the fly that is imitating it. When presenting a dun imitation to the trout, it has to be drag-free and from upstream, not giving a fish much opportunity to see the line or leader. This can be done by cross current reach cast. This way your fly will drift towards the trout before the line and the leader arrive. Hendrickson and Blue-Winged Olive are some of the patterns for mayfly duns.

Fishing Mayfly Spinner/Spent

Mayfly spinners that fall to the water surface are egg-laying females. Therefore, female coloration should be followed with a pattern imitation. They drop the eggs on calmer waters, over gentle riffles or flats and this is where you will spot spinners. When they fall to the surface (now known as spent) and lie motionless, the trout is more selective and in no rush to strike. The imitation has to be as accurate as possible to fool the trout. Using a floatant on your fly will help. Also, the presentation here is of a great importance – the best is to do it with no drag at all as these flies have no movement. Reach cast would work best.

spentmayfly - FrostyFly



There are so many great recipes for tying mayfly patterns. Here, we have selected a few of our video recipes that have proven effective and that you might find interesting to try. These recipes were created and tied by Jim Misiura and Tim Cammisa, awesome fly tiers. All recipes have easy-to-follow steps and explanations.

For mayfly dun patterns, check out the following:

For mayfly nymph patterns, see:

Check out our amazing mayfly patterns

Mayfly Life Cycle & How to Fish Mayfly Patterns - Realistic Mayfly Nymph
Hemingway’s Mayfly Nymphs
Mayfly Life Cycle How to Fish Mayfly Patterns Realistic Mayfly 9980 - FrostyFly
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Realistic Mayfly Dry II

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2 thoughts on “Mayfly – The Life Cycle & How to Fish Mayfly Patterns”

  1. Graham Muirhead

    Thank you so much for this article. It is a brilliant example of how to give the clearest and most easily understood explanation of each stage in the life of a mayfly I have read (and I have read far too many!).

  2. Great info, note that mayflies can go through from as few as 12 to as many at 45 instars depending on the species. But that most go through between 15-25 of them. Also, after each instar, the nymphs become a very light, almost white, color after shedding their old exoskeleton, becoming darker (more colorful) over time until the next instar occurs.

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