Mayfly life cycle
As spring warms and the sun stays out longer the keen angler will begin to see birds swooping low across the water and fish happily rising, a sure sign of a mayfly hatch. Dreams are made of casting a dry fly to a rising trout mouth! But first you need to know a few things- what freshly hatched aquatic insect the fish are eating and what fly do you have that will match. This month we will discuss a few of the more common mayflies and appropriate adult (DUN) imitations that you may want in your fly arsenal.
The mayfly life cycle can be broken into 4 parts: nymph, emerger, dun, spinner. Fish will eat at all of these phases and it helps to know what flies will be most successful during a hatch. The nymph is the underwater stage, fished with many of the subsurface flies described in last months blog. As the nymph begins to molt they will be propelled to the surface by gases collected under their exoskeleton. This begins to fall away, creating the ‘shuck’, as they break the surface of the water. Some mayfly nymphs crawl from the water, others float with the assist of the gas bubble.
During this stage of shedding the exoskeleton a mayfly is vulnerable. Many are not able to completely emerge from their nymphal stage and are called ‘cripples’. Others will be able to break completely free and float on the surface waiting for their wings to fill with fluid and harden. Trout will feed consistently, waiting for the next snack to float into their field of view. Dry fly fishing at its best!
If the ‘dun’ or adult mayfly survives this float on the water they molt again into a sexually mature adult or ‘spinner’. Giant clouds of mayflies form with mating spinners. Males will fall to the banks or water and die. Females will rest on vegetation waiting for the eggs to fertilize then return to the water to deposit them and die. The ‘spinner fall’ can happen that evening or the next morning.
With so many phases of a mayfly’s life you can see how having a varied selection of flies would be beneficial. Many mayfly imitations can cross between genus, and often the nymphal stage can be covered by fewer flies than the adult. Research hatch charts in your area to know what the most useful patterns may be for that time and pack accordingly. A few resources I found helpful were:
- Missoulian Angler Fly Shop https://www.missoulianangler.com
- Trout Nut website http://www.troutnut.com
- Henry’s Fork Anglers https://www.henrysforkanglers.com
Good luck and tight lines!
Blue Wing Olive, BWO, Baetis
These small mayflies hatch year-round, most common in the spring and fall, typically a grey wing with an dark olive green to grey colored, slender body. A smaller bug sizes 16-24, BWOs are a prolific hatch in cold, cloudy weather.
Blue Wing Olive Patterns –
- BWO Extended Body – This is a classic mayfly pattern consisting of a slender olive dubbing body, and gray or dun hackle at wrapped vertically at the thorax. The hackle allows this fly to float upright on the water surface making a great profile.
- BWO Parachute – A simple parachute fly that will ride lower on the surface, mimicking the newly emerged fly still filling out its wings. The parachute post makes for better visibility.
- Brooks’ Sprout Baetis – An emerger style fly sure to fool the most finicky trout. This fly rides in the surface of the water, its shuck still in the water, and dubbed thorax above with a small white foam post for visibility.
Flavilinea, Flav, Drunella flavilinea
A larger mayfly with 3 tails, dark gray wings, and a green to brown body. They are similar to their larger cousin the Green Drake, with a thicker abdomen and thorax. Hook sizes 12-14 work well. Flavs will typically be seen hatching on western rivers in June and July, on cloudy humid days.
Flavilinea Patterns (may use smaller Green Drake patterns) –
- Last Chance Cripple, Green Drake – This is a pattern that can be used for both the Flavilinea and a Green Drake. An emerger with a biot body, shuck tail, and CDC and hackle wing. Just breaking the waters surface this fly is a good choice during a hatch.
- CDC Thorax Flavilinea – A simple mayfly pattern with a stout abdomen. This fly will also ride at the surface as there is no vertical hackle to keep it floating high.
Gray Drake, Siphlonurus occidentalis
The Gray Drake can be found on both East and West coast waterways. This mayfly typically hatches June through July in the Western US. They have a gray wing with gray to olive bodies and darker brown markings. Flies in sizes 10-12 should work well.
Gray Drake Patterns –
- Adams (Parachute and Traditional) – The gray colored abdomen of a traditional Adams mayfly will do to imitate a Gray Drake. Select a Parachute style for better visibility and to ride lower on the water’s surface. A traditional Adams with hackle wings will ride higher. Either may entice that hungry Rainbow.
- Gray Wulff – A classic fly created by Lee Wulff for the Ausable River, this fly has a heavily hackled thorax and split hair wings to stay floating in the most turbulent waters.
Green Drake, Western Green Drake, Drunella grandis
This monster of a mayfly is a favorite of trout and fisherwomen alike! Coming in at hook size 8-12 the Green Drake is worth the effort for feeding trout from June to July. Green Drakes commonly emerge on cloudy, humid days with 3 tails and bright olive green bodies.
Green Drake Patterns –
- Green Drake Cripple – Again an emerger with the shuck of the insect below the surface. A biot or thread body, shuck, and hackle or CDC for floating. A similar colored Brooks Sprout would also work, making sure to have a larger hook size and more olive colored body.
- Hair Wing Green Drake – With the larger wing similar to an Elk Hair Caddis this fly will float and be visible in rougher water while still sitting at the surface.
Hexagenia, Hex, Hexagenia limbate
The Hexagenia are one of the largest mayflies. Sadly for stream anglers we won’t come across this fly. Hex live in the muddy bottoms of lakes or larger, slow moving rivers, often hatching in the late evenings of June to July, far enough off shore that you couldn’t cast to them. Hook sizes 8-14 should work for you lucky enough to have access to this hatch!
Hexagenia Patterns –
- Hexagenia Foam – A long bodied, heavy foam fly that is a trick to cast. Use larger tippet to help turn the fly over in your cast.
- Crystal Tail Hex Cripple – A very good imitation of an emerging Hexagenia, with Ostrich and flash to simulate the trailing shuck, and foam in the thorax to help keep it hanging at the correct angle.
Mahogany Dun, Paraleptophlebia bicornuta
This late season hatching mayfly, emerging late July through early October, may be the last hurrah we see for dry fly action. With the colder weather fish are more selective and spooky. The Mahogany Dun typically has a dark gray wing with mahogany brown body. Fished in sizes 14-18 will be your safest bet on those colder days.
Mahogany Dun Patterns –
- Tiltwing Mahogany – The slanted hair wing creates a realistic upright sail wing of a mayfly. The slimmer, rich brown biot body and horizontal hackle allow this fly to float at the surface level.
- Mahogany Parachute Extended Body – The horizontal hackle allows this fly to sit low on the waters surface, and the parachute post increases visibility. The extended body more accurately mimics the classic mayfly profile.
- Mahogany Spinner – The horizontal, splayed wings of a spinner fly replicate the final stage of a mayflies life. Having mated and deposited the next generation in the water the female falls to the surface with clear wings. Some mayflies retain their adult colors, others change to a rusty brown, hence another name ‘Rusty Spinner’.
March Brown, Western March Brown, Rhithrogena morrisoni
As their name implies March Browns are typically seen early in the season through run off. Sizes 12-16 should work well, however the tricky part is accessing those rising fish during high waters. The mottled wing and brown to black body are characteristic of the March Brown.
March Brown Patterns –
- March Brown Extended Body – The extended body of this fly may create a more realistic looking insect profile. The horizontal hackle allows it to float more even with the water surface while the parachute post or upright wings make it easier to follow in the current.
- Quill Gordon – A classic Catskill style fly that will still catch fish! The vertical hackle allow it to skitter across the waters surface, creating movement that fish often seek.
Pale Evening Dun, PED, Ephemerella dorothea dorothea
Pale Morning Dun, PMD, Ephemerella dorothea infrequens
PEDs and PMDs (or Sulphur if you are in the Midwest or East coast) are the same Genus, different Species. As the name implies the Pale Morning Dun hatches in the late mornings from June through August, while its evening counterpart the Pale Evening Dun gets to shine from the evening hours until after dark. The PED is more temperature dependent, preferring cooler summer nights and will wait until their preferred temperature before hatching. PEDs/PMDs come in shades of yellow, to olive and tan depending on the waterway. Have a variety of patterns, in sizes 14-20, in a few shades of yellow, with some pale olive or tan for good measure.
PMD/PED Patterns –
- Sparkle Dun PMD – This fly has a slender body, trailing shuck, and an upright wing from deer or elk hair. This style floats on the water surface imitating an emerging mayfly.
- Brook’s Sprout PMD – An emerger fly in the same style as Brooks Sprout Baetis, just a different color! This fly again is meant to sit at the water’s surface with the bend of the hook below. The material off the bend imitates the shuck still stuck to the emerging adult, the coloring is more correct for a PMD/PED, the horizontal hackle helps keep it floating and the foam post makes it visible.
- PMD Cripple – Another version of an emerging mayfly, a cripple typically uses a straight shank hook, vertical hackle, and deer hair wing. This fly also rides above and below the surface in a more vertical manner than the curve shank flies. Some may have a sparkly dubbed thorax.
- Comparadun PMD – Another low floating fly with a wing from elk or deer hair. The name ‘Comparadun’ describes the hair wing which extends side to side in almost 180 degrees providing a very stable floating fly.
Trico, Tricos, Tricorythodes minutus
Coming in at the smaller end of all mayfly species are the Tricos. This hatch is known for a giant spinner fall typically in the early morning after the prior days evening hatch and subsequent mating. However, they can also hatch in the mornings, making for a busy trout buffet! Tricos have white wings and tiny brown to black bodies, hatching July through October. Appropriate imitations would be in hook sizes 20-28.
Trico Patterns –
- Griffith Gnat – Usually used as a midge cluster a Griffiths Gnat will also work when the Trico hatch is on, imitating the clumps of hatching or spent flies that will cover the water. Some will have a small post to make them easier to spot.
- Hi Vis Trico Spinner – A parachute style spinner fly that makes it easy to see.