Lesson 2 | Mayflies

Learn About Mayflies

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This is the second lesson of our paid entomology course that we offer to you for free so you can see what it looks like and works like.  If you like what you see, you can buy the full course here.

Minnow_mayfly_nymph_Baetidae-960x636Mayflies are arguably the most elegant insect of the fly fishing world.  They vary in size and color and are a staple in the trout’s diet.  As fly fisherman, we imitate this order with patterns like the parachute adams, adams dry fly, pheasant tailcomparadun, and the mercury baetis.

Mayflies offer year round nymphing and dry fly fishing and are located across the world.  Some of the most prolific hatches are mayflies.  I have heard stories of snow plows unburying bridges that were swarmed with mayflies.  Baetis will hatch year round giving mayfly dry flies a necessary place in your box anytime you’re on the water.  In the spring and summer you have dozens of different species that hatch.  If it weren’t for mayflies, entomology would really be rather simple.  Mayflies hatch at all different times of years, the nymphs can look pretty different from species to species and they vary greatly in size.  It’s best to refer to local hatch charts and talk to local fly shops on the rivers you plan to fish to discover what flies are currently hatching, though with this knowledge and a seine, it isn’t necessary as long as your box is stocked.

mayfly nymph
mayfly nymph

In this course we will go over several, but not all of the major species of mayflies that are important to anglers.  What’s important to remember is with the knowledge in this course and a way to collect insects under and above the water (fishing seine) you can identify what you need to throw without any knowledge of what you are actually throwing.  You don’t need to know it’s a BWO, you need to know it’s a small olive mayfly with blue/grey wings.  Then match that to what is in your box and present it well for fish catching success.

How to identify a Mayfly

The key characteristics for a mayfly nymph are 3 tails and single pronged legs.  For emergers and dry flies, the sailboat like wings are the key to identifying it’s a mayfly.  They are delicate, slow flying and beautiful.  When the sunlight hits them, it’s something out of dream.  Though identifying the species from each other can be more of a challenge, mayflies themselves are likely the easiest dry fly to identify.  A spinner (dead dry fly) will often have the wings layed out to the sides on the water.

Mayflies have 2 wings that sit vertical, and have transparency to them and often detailed designs.  the nymphs have long legs, short antennae, and have  3 tails.  Some mayfly nymphs have 2 tails, but you can be certain that a 3-tailed nymph is a mayfly. 

Mistaking stonefly nymphs for mayfly nymphs is common for anglers.  Here’s the rules to identify the differences:

1- If it has 3 tails, it’s always a mayfly

2- If it has 2 tails, look at the legs.  Mayflies have one hook on their legs while stoneflies have two hooks on their legs.  If the foot doesn’t split into two, then it’s a mayfly.  

Check the tails first, then the legs and you should be able to tell the difference with ease.

Life Cycle of a Mayfly

For the angler, you only need to focus on the nymph, emerger, dry fly and spinner stages to catch fish.  Nymphs and dries are easily identifiable, and you can tell if the fish are eating emergers because when a fish rises to eat an emerger, you will rarely see a mouth and always see a tail.  This is because the emergers and the fish are actually near the surface but oriented down towards the bottom of the river waiting for the mayflies to detach and emerge and then they eat them and swim back down exposing their tail.  Let’s dive into the 4 stages of a mayfly that you need to know to catch more fish.


Mayfly Nymphs

mayfly-nymph-identification-diagramMayfly nymphs are broken down into 4 groups:  Swimmers, Clingers, Crawlers, and Burrowers.   Common entomology classes will distinguish these 4 types, but the reality is it doesn’t matter much to the angler.  If the goal is to match an identified insect from your seine to a fly in your box, then this knowledge, though interesting, isn’t of much value.  I haven’t heard many anglers say on the river, “Man, those crawler mayflies were way more productive than the burrowers today…”.    If we don’t imitate it as fly fishermen, we don’t really care.  Instead, the way in which it’s fished will determine what the fish are eating.  Most mayfly nymphs are imitated with the same patterns, but fished at different depths and different styles.  Swimmer nymphs for example can be stripped like a streamer to get a strike, burrowers, are often drifted along the bottom.   Identifying which bugs the fish are eating is always a process of elimination.  However, if you use a seine to see what’s in the water and choose the most prevalent insect found, you greatly increase your chance of success. In addition, most mayfly nymph patterns mimic all of these types with moderate accuracy so there isn’t always a need to decipher mayfly behavior patterns.

Hacklegill mayfly nymph (Potamanthidae)Burrowing_mayfly_nymph_Ephemeridae-960x637

Common colors and sizes

Colors: Black, white, brown, red, orange, yellow, olive, blue, purple, pink, tan
Sizes: #8, #10, #12, #14, #16, #18, #20, #22, #24, #26

Mayfly nymphs come in all colors and range in sizes #8-#26.  With a range this large, process of elimination or guesswork is difficult and time consuming.  It’s for this reason a seine is so valuable.  A 5 minute seine will show you the color and size of the mayfly nymphs in the water allowing you to match the insects faster and with better accuracy.  Most nymph patterns that have pheasant tails coming out the back imitate mayflies.  Mayfly nymphs, though 3-tailed, when in the water often slicks into one tail.  This is why the pheasant tail fibers work so well for a mayfly nymph imitation.

Flathead mayfly nymph (Heptageniidae)Minnow_mayfly_nymph_Baetidae-960x636

Pheasant tails, mercury baetis, lightning bug, skinny nelson, and others are great mayfly nymph imitations.  Often sparse, thin patterns with tails and beadheads do the best imitations.

Notice how the mayfly nymph patterns all look similar though have different colors?  The shape is the easiest way to tell if it’s imitating a mayfly.  These patterns have tails to imitate the three tails that mayfly nymphs have, and they also have legs towards the front of the body and are typically slender in shape compared to stonefly patterns.  Looking at any fly pattern, regardless of the name with the knowledge you have now should make it easy to identify mayfly nymph patterns.

Exceptions:  It’s true that some pheasant tails can imitate small stoneflies as well and a rubberleg PT can be used to imitate several insects, but the goal in identifying a pattern to a species is finding the design of the insect and matching it to the design of the pattern.  If the shape, size and color match close enough to the insect you found in you’re seine, that’s all you need to know. 

Tips on fishing mayfly nymphs

  • Fish any way you can – There is no wrong way to fish these really. Strip them, dead drift them deep or shallow with or without weight.  All methods have their place when catching fish.
  • Czech Nymphing for the win – I personally do a lot of Czech Nymphing with pheasant tails and variations of pheasant tails with great success in all kinds of rivers and sections in the river. I think the key here is to have one on your line as often as possible, unless your seine tells you otherwise.

Mayfly Emergers


mayfly emerging from its larval body and spreading it's wings
mayfly emerging from its larval body and spreading it’s wings

Mayfly emergers are likely one of the most important stages for trout fisherman to know and identify.  Emergers will have a shuck behind their bodies and will be fresh on the water or just below the surface.  It’s easy to tell if a trout is feeding on a mayfly emerger.  All you do is look to see if you can see the trout’s mouth.  Often, they will rise, you will see their tails but never their mouths or heads pop our of the water.  This is because trout are feeding just below the surface and feeding on emergers as mentioned above.  They could be eating midges or caddis, but that’s what the seine is for…

Common colors and sizes

Colors: Olive, brown, yellow, blue, green
Sizes: #10, #12, #14, #16, #18, #20, #22, #24

As with all mayflies, emergers range from sizes #10-24 and come in a variety of colors.  Gray is a good all around color profile, though most are more colorful and are olive, brown, yellow, blue, and green.

General tips for fishing mayfly emergers

If a river isn’t highly pressured, you should be able to fish emergers just like dries behind a dry fly as a 2-fly set up and do great.  If the fishing is pressured, letting the emerger float downstream to the fish is often a good method.  Regardless, having a small delicate strike indicator or a equivalent mayfly dry fly in front of your emerger is the best way to go unless you can sight fish.  This can often produce strikes on the dry as well as the emerger giving you 2 great chances to catch fish.


Excellent mayfly waters

Mayfly Dries

mayfly-dry-identification-diagramAdult mayflies are most often fished and easily identified.  They will have their wings intact and will be floating well on the water.  Though the dries spend little time on the water, this stage is the most popular dry fly fishing on most rivers.  If you get down to the fishes level on the river on a cloudy day, you will see a lot of these on the water and heads popping and slurping them down just as quickly.  Hatches can happen anytime of the day, though morning and evening are often the most prolific.

Common colors and sizes

Colors: Black, White, Brown, Red, Orange, Yellow, Olive, Blue, Purple, Pink, Tan
Sizes: #8, #10, #12, #14, #16, #18, #20, #22, #24, #26

Sizes #8-#24 in a bunch of different colors is the name of the game.  When the hatches are large, you won’t need a seine, just stand in the water and look at the water’s surface and you’ll be able to pick them out.  A seine helps collect them and identify color and size more easily, but it’s not always necessary with mayfly adults given their easy to identify profile.

mayfly dry
mayfly dry

The parachute adams, HL variant, Biot Parachute, Comparadun and other well known imitations best imitate a mayfly.

Tips for fishing mayfly dries

  1. 2-Fly Set Up – I always fish a 2 fly set up, though if you’re a beginner a single mayfly dry in the summer is often your best bet at catching a fish.  Fish it upstreaming and make sure not to create any drag on the fly in the water, it’s a dead giveaway when a fly skates on the water as a mayfly, and almost always, the fish will refuse the fly that way. 
  2. Pile Casts – A pile cast is a good cast to use if you are getting a lot of drag on your dry fly presentation.  Stop your forward cast early and then slowly follow your piled up fly line to the water and you’ll get more strikes as it produces a drag free drift for longer.
  3. Smaller Flies Win – If in doubt, always go a size or two smaller than the naturals you find in the water.  This helps the trout’s willingness to eat and will catch you more fish.  If you have trouble seeing the smaller flies, use the first tip and put a larger fly on the front of the two fly set up.

Common Mayfly Hatches

This is where it can get complicated, so we are going to do our best to simplify this for you. There are several dozen different mayfly hatches that occur worldwide and they are different sizes, colors and hatch different times of year and during different times of the day. We are going to provide a concise bullet list that shows the most popular hatches so you can have reference. This is not a complete list as that would take another 20 years to complete, but here are the most important ones:

Blue Wing Olives

bwo-male-mayfly-dryCommon names are BWO, Baetis and Blue Wing Olives.


  • Nymphs: Baetis/BWO are shaped like bullets and are built to swim quick in the water. They are swimmer mayflies and in the nymph form are small and slender.  Slender tied pheasant tails in black, purple or olive are excellent baetis patterns for nymphs
  • Emergers/Dries: As they begin to emerger, they take on a grey and black wing casing.  This grey, chalky blue to black wings are visible slightly on emergers, but very visible on the dry/adults.  Slender bodies, often no larger than a #16 (most 18-24) and they tend to like colder spring/fall weather and even windy days with cloud cover.
  • Colors and Sizes: Olive/Grey in sizes #16-#24
  • Hatch Seasons: Spring – Summer – Fall – Winter
  • Hatch Time of Day: Morning and Evenings


Common names are speckled duns, grizzly quills.

Typically found in lakes and slow moving water, Callibaetis are a stillwater anglers best friend.  They are often speckled or have alternating barred lines on them that are tan/white/grey to black/brown.  Grizzly hackle is a great material to use to imitate this variegated color on callibaetis.  The nymphs are strong swimmers as well and very slender.  The adults will spend ample time on the water making dry fly fishing both challenging and fun.

  • Colors and Sizes: Tan, Grey and Dark Brown in sizes #14-#18
  • Hatch Seasons: Spring – Summer – Fall
  • Hatch Time of Day: Mornings and Evenings

Pale Morning Duns

pmd-dryCommon names are PMD, PED, Sulphurs, Pale Evening Duns

Pale morning duns are a summer and early fall bug in most places of the world.  Often morning and evenings (hence the name) are when you’ll find them.  The nymphs are dark brown and gold/yellow often striped.  They vary greatly by region so matching what you find in your seine is important and finding the adults is a dead giveaway to the nymphs below the surface.

  • Colors and Sizes: Yellow and Tan in sizes #14-#22
  • Hatch Seasons: Summer – Fall
  • Hatch Time of Day: Morning and Evenings



Frustrating little insects but also my favorite.  They are very small both as nymphs and dries and as spinners.  Due to their behavior, they are best known for their spinner falls and spinner patterns take the majority of fish.  The nypmhs are bit thicker and pudgier than you’d expect and small stocky nymph patterns work well.  They are brown and yellow mixed as nymphs but are black and white as they emerge and become dries.

  • Colors and Sizes: Black or White in sizes #18-#26 (Brown/Yellow as nymphs)
  • Hatch Seasons: Late Summer – Early Fall
  • Hatch Time of Day: Early Morning with Spinner falls until noon

Tricos Flying and Being Eaten

Hex Mayflies

Common names are giant michigan mayfly, lead-winged drake, big yellow may.

mayfly dry
mayfly dry

These are big yellow mayflies and as nymphs they are big and brown.  Often mistaken for stoneflies due to their size, they are just big mayflies both as nymphs and as dries.  The dries are easy since they are so large and yellow and you can often see their front legs coming out in front of the body as a dead giveaway to it being a hex (if the large size didn’t do that in the first place)  The nymphs are easy to identify as well since they are often quite large and bear a similar color of yellow to tan as the adults.

  • Colors and Sizes: Yellow and tan in sizes #8-#14
  • Hatch Seasons: Summer – Early Fall
  • Hatch Time of Day: Evenings into Night

Isonychia Mayflies

Common names are slate drakes, leadwing coachmans, Isos, grey drakes, Mahogany Duns

green drake on left, isonychia (slate drake) on right
green drake on left, isonychia (slate drake) on right

This nymphs can appear fuzzy as they have gills along their body and are good swimmers and are brown in color. They can get as big as a size #8, but most are #12-#16.  The emergers come out of the water and onto the banks in some places making the emergers useless while in other places they come right out of the river like a typical mayfly and take an extraordinary amount of time to emerge into adults.  This makes the mayflies very important as an emerger pattern. Chocolate, black and shiny black colors imitate the emergers well and as they become adults, black, brown and dark dark olive is a good option.

These are also often called mahogany duns and can be a light reddish color as seen in the image.

  • Colors and Sizes: Brown, Mahogany and Grey in sizes #12-#16
  • Hatch Seasons: Summer – Fall
  • Hatch Time of Day: Evenings

Green Drakes

Green drake nymphs cling and crawl on the stream bed and are easy to identify because their tails all form together to make what looks like a sharp point.  They have bulky legs for their size and look short and stocky.  They are brown colored and are found in clean rivers most times and is a sign of good water health if you find them.

  • Colors and Sizes: Olive/Grey in sizes #8-#14
  • Hatch Seasons: Spring – Summer – Winter – Fall
  • Hatch Time of Day: Afternoons and Evenings

March Browns

Common names are Gray Fox, March Browns

March brown nymphs are the reason hares ears and pheasant tails are so popular.  They imitate the nymphs so well and they are common in a lot of rivers. Tannish to brown is their colors as nymphs and they have three well noted tails and a slender body that bulks up towards the head with noticeable legs.  That’s a very common mayfly nymph shape and if you find them in rivers, they are easy to imitate.  The adults are also easy to imitate with parachute adams as they are tan to grey to light brown in color and standard sizes are #12-16 for most areas.  Though a spring bug, you can find them as nymphs in the water most of the year from Jan to July.

  • Colors and Sizes: Brown, Tan, Gray in sizes #10-#18
  • Hatch Seasons: Spring- Early Summer
  • Hatch Time of Day: Morning and Evenings


Common names are light cahill, ginger quill

Again very similar to a PT or hares ear, they are tan, yellow and brown in color and have a very traditional mayfly look in both nymph and dry fly form.  They are lighter colored as dries and can be white or tan.  Callibaetis patterns work well in a pinch if you don’t have any exact patterns.  These are often confused with PMD cause they are similar in color and hatch during the same time of year.  It pays off to collect and find these insects on the water cause the hatches are sporadic and often the reason you think they are PMD but actually cahills.

  • Colors and Sizes: White, Tan, Cream in sizes #12-#18
  • Hatch Seasons: Summer – Fall
  • Hatch Time of Day: Sporadic Throughout the Day


Thought I’d just make this clear. Adams is not a type of mayfly. A parachute adams is a fly pattern that imitates a variety of mayflies. NEVER ask another fly fisherman if the adams are hatching. Unless you just wanna mess with them… 🙂

Mayfly Spinners

spinnerfliesLikely one of the most important stages to pay attention to and the easiest to identify.  These are mayflies that are falling back to the water after mating.  They don’t really move on the water as most are dead or close to dead and they are easy prey for trout.  The key to identifying these is simple.  You’ll see them on the water with wings fallen to the sides.  These flies are dead, not moving…dead.  Pretty hard to get that wrong.

Common colors and sizes

Colors: Black, White, Brown, Red, Orange, Yellow, Olive, Blue, Purple, Pink, Tan
Sizes: #10, #12, #14, #16, #18, #20, #22, #24, #26

The best size for spinners is one size smaller then what’s on the water.  Fish get picky and selective when eating spinners so it pays to be small, delicate and well-presented.  I’ve caught some very large fish on mayfly spinners however, so don’t be scared away from the fact they are harder to see and fish.

mayfly-bwo-spinnerAll spinner patterns have their place and are often called “insert species name here”  spinner.  For this reason it’s easy to tell it’s a spinner by the name and profile of the pattern.  To match an insect to a fly in your box, use your bug seine to identify the color and size not forgetting to go a size smaller than what is found.  Even looking to the river banks where spinners pile up is a clever way to identify the insects the trout are eating.

Tips for fishing mayfly spinners

  • 2 Fly Set up or Strike Indicator – A 2 fly set up or a small strike indicator like the NZ strike indicator makes it 100x easier and is recommended, making it easier to see and fish.
  • Target fish – Most times with spinners, you’ll fish to actively rising fish, not blind casting. Fish get into a rhythm with spinners.  Correctly time that rhythm and match the hatch with a drag-free presentation and you’re a sure bet for a successful eat.
  • Presentation is everything – When fishing spinners, fish are often in slow, slack water and right next to the surface. They feel vulnerable and any reason to stop feeding is reason enough for them.  A poorly made cast, or casting the line over the fish, or landing the line so it passes over the fish first are all great ways to put the fish down (startle them and cause them to stop feeding) and lose your chance of catching him.  Often times, a cast from upstream down to the fish is the best way to get a take if you can position yourself correctly without spooking the fish in the approach.

The Bugs Covered in Our Entomology Course

midge adults


Midges are present in a river and lake system year round making them a key insect to understand and identify when you’re on the water. Learn how to identify a midge in all stages, match it to a fly in your box and catch more fish. Includes tips on how to fish each stage of midge insects


Mayflies are the most diverse insect a fly fisherman needs to identify and understand. Learn the stages, flies to use, how to fish those flies and common hatches, colors and sizes to watch out for in the river and lakes around the world.

caddis nymph
caddis nymph


Caddis are an exciting and highly important insect to trout. Learn what stages hold the most importance to trout and how to match them to flies in your box. We also provide some critical tips to improve your presentation on the river.

stonefly nymph
stonefly nymph

Stoneflies & Terrestrials

We cover the most exciting bugs to fish in this lesson – stoneflies and terrestrials. Though not alike in many ways, they are fun to fish and are known for producing great summer fishing. Learn about the elusive stonefly and the coveted terrestrials including patterns and tips on how to fish them.


Scuds, Sowbugs & Annelids

These insects are fully aquatic and don’t hatch, yet they hold a vital importance to a trout’s diet. Learn about the underworld life of scuds, sowbugs and annelids (worms) so you can catch more fish, especially on tailwaters.

Dragonflies, Damselflies and Water Boatman

dragon dry
dragon dry

Fly anglers who love fishing lakes need to pay special attention to this lesson. However, if you prefer rivers, you’d be surprised how many of these insects reside in your local waters and are important to trout throughout the seasons. Learn the insects, patterns and tips on fishing them in this lesson.

Next Lesson | Caddis

Learn About Caddis