Fly Fishing Entomology
Mayflies
Mayflies 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 tail, comparadun, 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.
In this course we will go over many, 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.
- Mayfly
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.How to Identify Mayflies vs Stoneflies
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. As a general rule (not always but often), you will see more prominent and visible antennae on the front of stoneflies and thicker tails. This can vary of course, but often it is an easy way to ID them as well when you’re trying to figure out if the insect you’re looking at is a stonefly nymph or a mayfly nymph.Mayfly vs Stonefly
- Mayfly
- Stonefly
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
A Staple Meal for All Trout
Mayfly Nymphs
Mayfly 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.
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.
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.
Mayfly Nymphs
Mayfly 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.
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.
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.
Mayfly Nymph Patterns
- Mayfly
Mayfly Nymph Patterns
- BH Hares Ear #14-18
- Prince Nymph
- Olive Hares Ear
- Black Hares Ear
- BH Pheasant Tail
- Improved Pheasant Tail
- Improved Pheasant Tail
- Isonychia Pheasant Tail
- Mercury Baetis (BWO)
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 for Fishing Mayfly Nymphs
- Change your presentation: Mayfly nymphs behave differently depending on the species—some cling to rocks, some swim, and others get knocked loose and drift with the current. If trout aren’t responding, adjust how you fish them. Try a dead drift for clingers, a lift at the end of your drift to mimic an emerging nymph, or add slight jigging motions with a tight-line rig to imitate an active swimmer.
- Try beadhead and standard nymphs: Beadheads help your fly sink quickly, but they also add extra bulk that can turn off selective fish. If trout are ignoring your beadhead nymphs, try switching to a standard (non-bead) version and use split shot above the fly to maintain depth while keeping a more natural profile.
- Use a seine and the “dinner plate” method: Matching the hatch isn’t just for dry flies—it’s just as important when nymphing. Instead of guessing, use a seine net to check the exact size and color of the nymphs drifting in the water. Don’t just look at what’s available (“menu method”); focus on what the fish are actually eating (“dinner plate method”), which is covered in detail in the course conclusion.
Mayfly Emergers
The Rise Generates Strikes
Mayfly Emergers

Mayfly emergers represent a critical stage for trout anglers to recognize and understand. As mayflies transition from their larval form, they leave behind a distinctive shuck while ascending to the surface. Trout feeding on emergers display telltale behavior—their tails break the surface while their mouths remain submerged, indicating subsurface feeding. While this behavior might suggest midge or caddis consumption, a seine sample provides definitive identification.
Common Colors and Sizes
- Colors: Gray, olive, brown, yellow, green, orange, black
- Sizes: #10–24
Mayfly emergers vary widely in size and color, typically ranging from sizes #10 to 24, depending on the species and region. While gray is a solid all-around color, many emergers display more vivid hues, including olive, brown, yellow, blue, and green. These subtle variations often make a significant difference, especially when trout become selective during a hatch. Paying attention to the specific color tones of the naturals on the water will help you refine your fly selection and increase your chances of success.
Unlike nymphs, which drift along the bottom or mid-column, emergers represent the transition stage between nymph and adult. At this point, the insect is rising toward the surface, often trapped in the surface film, making it an easy target for feeding trout. Because of this, emergers can be fished in a variety of ways—either at the bottom right along with a nymph, mid-column, or even as part of a dry-dropper setup where the emerger is the dropper. Matching both the shape and movement of the natural insects is essential. Soft-hackle patterns, for example, do an excellent job of imitating the lifelike motion of an emerging mayfly and can even trap air bubbles, increasing the life-like imitation of those patterns. Insects will often use air bubbles to rise to the surface and break the water surface tension. Trout will key in on those bubbles and insects.
Many classic patterns effectively represent mayfly emergers, including the RS2, Sparkle Dun, Barr’s Emerger, and soft-hackle Pheasant Tail Nymph. These flies share common characteristics: they are thin, sparse, and often include trailing shucks or soft-hackle fibers to mimic the struggling movement of an insect breaking through the surface. Some emergers float low in the film, while others hang just beneath the surface, requiring slight adjustments in presentation.
Foam-back emergers are designed to be fished deeper in the water column, where their buoyant materials naturally cause them to rise toward the surface. This movement closely imitates an emerging mayfly making its ascent, often triggering aggressive strikes from trout. Conversely, unweighted emergers perform best when fished just below the surface or in the surface film, where they effectively imitate insects that are trapped or struggling to break through. Choosing the right pattern depends on where trout are feeding and how the mayflies are emerging in the water column.
Since mayfly emergers are a prime food source for trout during a hatch, presentation is just as important as pattern choice. A dead drift often works well, but adding occasional twitches or a subtle lift at the end of the drift can trigger strikes. Trout often key on emergers just before the main hatch begins, making this an important stage to fish effectively.
Tips for Fishing Mayfly Emergers
- Fish it behind a dry fly for a delicate presentation: A two-fly setup with an emerger trailing behind a dry fly is one of the best ways to target trout feeding just below the surface. The dry fly acts as both an indicator and a natural attractor, helping you track your emerger in the surface film. Since trout often sip emergers in slow, clear water, this setup allows for a soft, drag-free presentation that won’t spook wary fish.
- Use soft hackles and the wet-fly swing: A soft hackle fly is a great way to imitate an emerging mayfly, especially when trout are feeding mid-column. Fish it using a wet-fly swing, letting the current carry your fly across the river. As your line straightens at the end of the drift, the fly will rise—a prime trigger for strikes.
- Make it the last fly in a two-fly nymph rig: When trout are feeding on early emergers before they reach the surface, adding an emerger as a dropper behind a heavier nymph can keep it in the strike zone. Foam-back and glass-bead emerger patterns work well in this setup, as they hover naturally while the nymph anchors them at the right depth.
Mayfly Emerger Patterns
- RS2 Emerger
- RS2 Emerger
- RS2 Emerger
- Foxtail Emerger
- CDC PMD Cripple
- Green Drake Emerger
- Adams Emerger
- BWO Emerger
- PMD/BWO Cripple Emerger
- Barrs Emerger
Mayfly Dries
The Subtle Dry Fly
Mayfly Dries
Adult mayflies are one of the easiest insects to identify on the water, thanks to their distinct upright wings, delicate bodies, and slow-floating nature. Unlike caddisflies, which have a tent-like wing shape, mayflies hold their wings straight up like tiny sailboats. Their bodies are slender, with two or three long tails trailing behind them. If you see a fly drifting lifelessly on the surface with upright, transparent wings and a thin, segmented body, it’s almost certainly a mayfly.
One of the key features of a mayfly adult is its wing shape and posture. Their wings are often lightly veined and can appear almost glass-like in the right light. These insects are also slow fliers and frequently get blown around by the wind, making them vulnerable on the water. Unlike stoneflies or caddis, mayflies do not skitter across the surface—they drift, often in a straight line, until a trout decides to eat them. During a hatch, you’ll see them accumulating in back eddies, slow seams, or the edges of riffles, where trout can leisurely sip them down.
If you’re unsure whether you’re looking at a mayfly adult or another insect, check the way it rests on the water. Mayfly duns (freshly emerged adults) will sit high on the surface film, supported by their wings and tails, while spent spinners (post-mating adults) will lie flat, with their wings spread out to the sides. This resting position, along with their delicate, upright wing structure, makes them easy to spot during a hatch.
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.
The parachute adams, HL variant, Biot Parachute, Comparadun and other well known imitations best imitate a mayfly.
Tips for fishing mayfly dries
- 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.
- 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.
- 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.
Mayfly Dry Fly Patterns
- Cahill/PMD
- General Adams
- Olive Parachute Adams
- Black Parachute Adams
- Parachute Adams
- Irresistable Adams
- Trico/General Mayfly
- PMD Mayfly
- Parachute Royal Coachman
- Parachute Hares Ear
- Parachute Green Drake
- General Parachute Adams
- PMD/PED
- Parachute BWO
- Trico
- BWO
- PMD
- BWO
Common Mayfly Hatches
Mayfly Hatch Info & Hatch Chart
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 detailed bullet list that shows the most popular hatches so you can have reference. This is not a complete list but they are the most important ones.
Blue Wing Olives
Common Names: BWO, Baetis, Blue-Winged Olives
Identification
- Nymphs: Baetis/BWO nymphs are shaped like bullets and built to swim quickly through the water. These swimmer mayflies are small and slender, with streamlined bodies. Slender-tied pheasant tails in black, purple, or olive are excellent Baetis patterns for nymphs.
- Emergers/Dries: As they begin to emerge, they develop grey and black wing casings. This grey, chalky blue-to-black coloration is slightly visible on emergers and very noticeable on adults. Their slender bodies are typically no larger than a size #16 (most are #18–#24). They prefer colder spring or fall weather and thrive on windy days with cloud cover.
Habitat
- Most Likely: Rivers, streams, and tailwaters
- Occasionally: Lakes with adequate oxygen and rocky bottoms
Seasonality and Hatch Timing
- Hatch Seasons: Spring, Fall, Winter (occasional summer hatches)
- Hatch Time of Day: Mornings and evenings
- Water Temperature Range: 40–60°F
Fishing Tips
- Slow Drift Technique: Use a soft hackle emerger pattern on a drag-free drift just below the surface. This is especially effective in slower pools and eddies where emergers gather.
- Double Dry Fly Rig: Pair a small BWO dry with a CDC emerger as a dropper. This setup increases visibility and gives trout a choice between a surface and near-surface offering.
- Match the Wind: On windy days, fish along wind lanes where trapped adults collect. Use a light tippet to minimize drag and ensure a natural presentation.
Key Fly Patterns
- Split-Back BWO: Olive body with grey thorax, sizes #18–#22
- BWO Soft Hackle Emerger: Olive body with partridge hackle, sizes #16–#20
- Hi-Vis Baetis Dun: Chalky blue-to-grey body, white post for visibility, sizes #18–#24
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West
Blue Wing Olive
Sizes: #16 – #24
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Region: Northwest
Blue Wing Olive
Sizes: #16 – #24
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Region: East
Blue Wing Olive
Sizes: #16 – #24
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Region: Southeast
Blue Wing Olive
Sizes: #16 – #24
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Region: Midwest
Blue Wing Olive
Sizes: #16 – #24
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Callibaetis
Common Names: Speckled Duns, Grizzly Quills, Pond Mayfly, Stillwater Duns, Calibaetis, Speckled Wings
Identification
- Nymphs: Callibaetis nymphs are strong swimmers with long, slender bodies and alternating barred patterns on their exoskeletons. These nymphs are most active in stillwater environments where they can dart between vegetation and open water. Patterns like the Flashback Pheasant Tail or Callibaetis Nymph are excellent imitations.
- Emergers/Dries: Emergers display a subtle shimmer from their exoskeleton and developing wings, with tan to grey tones. Adult Callibaetis, often referred to as Speckled Duns, have distinctively barred wings and alternating dark and light segments on their bodies. They are typically sizes #14–#18, with coloration varying from tan and grey to darker brown shades. Adults spend significant time on the water, making them an inviting target for trout.
Habitat
- Most Likely: Lakes, ponds, and slow-moving sections of rivers
- Occasionally: Backwaters or eddies in larger rivers
Seasonality and Hatch Timing
- Hatch Seasons: Spring, Summer, Fall
- Hatch Time of Day: Late mornings through early afternoon, often peaking during calm, sunny weather
- Water Temperature Range: 50–68°F
Fishing Tips
- Slow Retrieve for Nymphs: Use a floating or intermediate line and retrieve nymph patterns slowly with short, subtle strips to mimic the swimming action of Callibaetis nymphs.
- Focus on Wind Lanes: During a hatch, Callibaetis adults often collect in wind lanes. Position yourself to cast along these lanes, where trout are likely to be feeding.
- Long Leaders for Stillwater Dries: Use a long, fine leader (12–15 feet) when fishing dries to reduce surface disturbance and increase presentation accuracy.
Key Fly Patterns
- Flashback Callibaetis Nymph: Tan body, flashback thorax, sizes #14–#18
- Speckled Spinner: Grizzly hackle, light tan or grey body, sizes #14–#18
- Paraloop Callibaetis Dun: Grey or tan body, upright wing loop, sizes #14–#18
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West
Callibaetis Sizes: #12 - #18
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Region: Northwest
Callibaetis Sizes: #12 - #18
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Region: East
Callibaetis Sizes: #12 - #18
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Region: Midwest
Callibaetis Sizes: #12 - #18
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Pale Morning Duns (PMD)
Common Names: PMD, PED, Sulphurs, Pale Evening Duns
Identification
- Nymphs: PMD nymphs are slender and exhibit dark brown to golden-yellow bodies with distinct stripes or banding. These crawler mayflies are commonly found in riffles and slower sections of rivers, where they cling to rocks and vegetation. Patterns like the Split-Back PMD Nymph or Barr’s PMD Nymph work well to mimic their natural appearance.
- Emergers/Dries: PMD emergers display pale yellow to tan bodies with wings transitioning from grey to light tan as they mature into adults. Their delicate upright wings and slender bodies make them a favorite for dry fly fishing. Adult sizes typically range from #14 to #22, with a focus on sizes #16–#20 for most regions.
Habitat
- Most Likely: Rivers and streams with moderate to slow currents
- Occasionally: Lakes with rocky shorelines or nearby vegetation
Seasonality and Hatch Timing
- Hatch Seasons: Summer and Fall
- Hatch Time of Day: Late morning through early afternoon; evenings during cooler days
- Water Temperature Range: 55–65°F
Fishing Tips
- Upstream Nymphing: Drift PMD nymph patterns in riffles and transition zones where nymphs migrate before hatching. Use a light split shot to keep your fly in the strike zone without snagging the bottom.
- Emerger Focus: During a hatch, fish CDC PMD Emerger patterns in the surface film with a slow, drag-free drift to target selective trout.
- Spinner Fall Tactics: In the evening, look for spent PMD spinners on the water. Use a Rusty Spinner or PMD Spinner pattern for effective presentations, especially in flat, calm sections of the river.
- Sulphers vs PMDs: Keep in mind that while sulpher duns and pale morning duns and even pale evening duns are different species, they are similar enough in color and size and hatch ranges to use the same patterns. For simplicity and remembering these, it’s all the same bug. Sulphurs live out east, PMD and PME’s are in the west.
Key Fly Patterns
- Split-Back PMD Nymph: Gold and brown body, yellow thorax, sizes #16–#20
- CDC PMD Emerger: Pale yellow body with CDC wing, sizes #16–#20
- PMD Sparkle Dun: Light tan body with trailing shuck, sizes #16–#22
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West, Northwest, East, Southeast, Midwest
PMD Sizes: #14 - #20
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Tricos
Common Names: Tricos, Tricorythodes
Tricos are frustrating little insects but also my favorite hatch. They are very small, from nymphs to spinners. They are best known for their spinnerfalls, and most Trico-eating trout are caught on spinner patterns. The nymphs are a bit thicker and pudgier than you’d expect, so small, stocky nymph patterns work well. They are brown-and-yellow as nymphs but are black and white as they emerge and become duns.
Identification
- Nymphs: Trico nymphs are small but stocky, with a thicker, rounded body compared to many other mayflies. Their coloration is typically brown and yellow, blending well with the riverbed. Effective imitations include micro-nymph patterns tied in dark brown or yellow, sizes #18–#24.
- Emergers/Dries: Upon emergence, Tricos transition to a striking black-and-white coloration. Their small size and delicate wings make them challenging to spot on the water, but their spinner falls are a reliable indication of their presence. Dry flies should focus on the slender, upright body and transparent wing profile typical of Tricos.
Habitat
- Most Likely: Rivers and streams with slow to moderate currents
- Occasionally: Spring creeks and tailwaters with consistent flow and oxygen levels
Seasonality and Hatch Timing
- Hatch Seasons: Late Summer to Early Fall
- Hatch Time of Day: Early morning, with spinner falls extending until midday
- Water Temperature Range: 60–70°F
Fishing Tips
- Spinner Fall Focus: During spinner falls, use patterns like the Trico Spinner or CDC Trico to target rising trout in calm water. Focus on flat water where trout sip spent spinners.
- Long Leaders for Small Flies: Use leaders of 12–15 feet to reduce drag and allow delicate presentations, which are essential for these small patterns.
- Nymphing Success: Before spinner falls, fish small stocky nymph patterns in riffles or slower runs where nymphs gather before emergence. A two-fly nymph rig with a micro-nymph and unweighted dropper is often effective.
Key Fly Patterns
- Rusty Trico Spinner: Black or dark brown body with spent wings, sizes #20–#26
- Trico Comparadun: Black or grey body with upright wings, sizes #18–#24
- Micro Mayfly Nymph: Brown and yellow, slender profile, sizes #18–#24
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West, Northwest
Trico Sizes: #18 - #26
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Region: East, Southeast, Midwest
Trico Sizes: #18 - #26
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Hexegenia (Hex)
Common Names: Giant Michigan Mayfly, Lead-Winged Drake, Big Yellow May, Hex

Identification
- Nymphs: Hexagenia nymphs are large, burrowing mayflies with robust, tan-to-brown bodies. They are often mistaken for stoneflies due to their size but can be distinguished by their rounded body and visible gills along their abdomen. Effective nymph patterns include large, weighted designs like the Hex Nymph to imitate their bulky profile.
- Emergers/Dries: Hexagenia adults, commonly called “Hex,” are easily recognized by their large size and yellow coloration. Their front legs extend forward prominently, a defining characteristic. Dries are typically sizes #8–#14 and thrive in calm evenings, often accompanied by spinner falls just after sunset.
Habitat
- Most Likely: Slow-moving rivers, lakes, and ponds with silty or muddy bottoms
- Occasionally: Backwaters and oxbow lakes connected to rivers
Seasonality and Hatch Timing
- Hatch Seasons: Summer to Early Fall
- Hatch Time of Day: Late evenings into night, often peaking just after sunset
- Water Temperature Range: 60–70°F
Fishing Tips
- Evening Hatch Focus: Fish Hex dries during calm evenings near vegetation or along silty riverbanks. Look for large rises near sunset and present your fly delicately in low light conditions.
- Burrowing Nymph Strategy: Target Hex nymphs in muddy bottoms using heavily weighted patterns drifted close to the substrate. Adding slight movement can mimic their burrowing behavior and attract strikes.
- Night Spinner Fall: After the hatch, Hex spinners often collect on the water. Use a Hex Spinner pattern during the night, focusing on quiet pools or eddies where trout feed on spent adults.
Key Fly Patterns
- Hex Nymph: Brown and tan with heavy weight, sizes #8–#12
- Extended Body Hex: Yellow or cream body with upright wings, sizes #8–#14
- Hex Spinner: Spent-wing design in tan or light yellow, sizes #10–#14
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West, Northwest, East, Southeast, Midwest
Hexegenia Sizes: #6 - #12
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Isonychias
Common Names: Slate Drakes, Leadwing Coachmans, Isos, Grey Drakes
Identification
- Nymphs: Isonychia nymphs are strong swimmers, characterized by their fuzzy appearance due to gills along their bodies. Their coloration ranges from dark brown to mahogany. Typically found clinging to rocks in moderate to fast-moving currents, these nymphs are sizes #12–#16, though some can reach size #8. Weighted patterns like the Iso Nymph or Chocolate Nymph are highly effective for imitating them.
- Emergers/Dries: Depending on the region, emergers either crawl onto banks to molt into adults or emerge directly from the water. This variability makes emerger patterns critical. Emergers are typically chocolate, shiny black, or mahogany in color. As adults, Slate Drakes have slender, dark bodies in shades of black, brown, or dark olive and upright wings. Sizes range from #12 to #16.
Habitat
- Most Likely: Rivers and streams with moderate to fast currents
- Occasionally: Tailwaters and spring creeks with stable flow
Seasonality and Hatch Timing
- Hatch Seasons: Late Spring (May–June) in the East; Summer to Fall elsewhere
- Hatch Time of Day: Evenings, particularly on warmer days
- Water Temperature Range: 55–65°F
Fishing Tips
- Drift Nymphs Along Riffles: Cast weighted Iso Nymph patterns into riffles and allow them to drift naturally. A dead-drift presentation with occasional twitches mimics the swimming behavior of Isonychia nymphs.
- Focus on Emergers: When emergers are active, use patterns like the Iso Emerger fished in the film. Pay close attention to slower eddies where trout target emergers struggling to break through the surface.
- Twilight Dries: During evening hatches, fish adult patterns like the Leadwing Coachman on calm stretches of water. A long, drag-free drift will increase your chances of enticing a rise.
Key Fly Patterns
- Iso Nymph: Dark brown with ribbed body, sizes #12–#16
- Iso Emerger: Shiny black or mahogany body, CDC wing, sizes #12–#16
- Leadwing Coachman: Dark brown or olive body, upright wings, sizes #12–#16
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: East
Isonychia Sizes: #12 - #18
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Region: Southeast
Isonychia Sizes: #12 - #18
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Region: Midwest
Isonychia Sizes: #12 - #18
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Mahogany Duns
Common Names: Mahogany Dun, Paraleptophlebia, Rusty Dun
Identification
- Nymphs: Mahogany Dun nymphs are clingers, typically found in moderate to slower current. They’re small, with a reddish-brown or mahogany hue. Their flattened bodies and strong legs help them cling to rocks and debris. Pheasant Tail and Hare’s Ear nymphs in rust or brown shades work well as imitations.
- Emergers/Dries: These mayflies are known for their deep, reddish-brown bodies and medium-gray wings. They tend to emerge later in the season, often during crisp fall afternoons. Emerger patterns that sit low in the film are especially effective.
Habitat
- Most Likely: Small to medium streams, often with clear, clean water
- Occasionally: Larger rivers with slower runs and tailouts
Seasonality and Hatch Timing
- Hatch Seasons: Late Summer – Fall
- Hatch Time of Day: Afternoons, especially on warmer days
- Water Temperature Range: 48–60°F
Fishing Tips
- Focus on Soft Water: Target soft seams and slower-moving pools where trout can comfortably feed. A low-riding emerger pattern often fools selective fish during sporadic Mahogany Dun hatches.
- Match the Rise Forms: Look for subtle sipping rises. Trout feeding on mahoganies tend to rise more gently compared to their behavior during a caddis hatch.
- Keep It Sparse: These duns have a simple profile. Use slim-bodied dries and emergers with minimal hackle for a more natural presentation.
Key Fly Patterns
- Mahogany Dun Sparkle Emerger: Rust-brown body with an antron shuck, sizes #14–18
- Parachute Mahogany Dun: Mahogany body, white post, and dark dun hackle, sizes #14–18
- Rusty Pheasant Tail Nymph: Slim profile with a dark wing case, sizes #16–20
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West, Northwest
Mahogany Dun Sizes: #14 - #20
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Region: East, Midwest
Mahogany Dun Sizes: #14 - #20
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Gray Drakes
Common Names: Gray Drake, Speckled Drake, Siphlonurus Mayfly
Identification
- Nymphs: Gray Drake nymphs are burrowers, often found in slower-moving water with sandy or silty bottoms. They have elongated, streamlined bodies and are strong swimmers, often darting quickly to escape predators. Pheasant Tail Nymphs tied with a slightly thicker thorax and brown or gray bodies work well.
- Emergers/Dries: The emerging Gray Drake is often speckled with distinct, patterned wings and a grayish-brown body. They tend to emerge sporadically rather than in heavy, predictable hatches. The adults are known for their mottled wings and slender bodies, and spinner falls often occur at dusk over slow water.
Habitat
- Most Likely: Slow-moving rivers, spring creeks, and lakes
- Occasionally: Larger rivers with silty or sandy bottoms
Seasonality and Hatch Timing
- Hatch Seasons: Late Spring – Early Summer
- Hatch Time of Day: Evenings, often near sunset
- Water Temperature Range: 55–65°F
Fishing Tips
- Focus on Slow, Silty Areas: Gray Drakes prefer slower, silty water. Fish emerger patterns along seams and foam lines in pools and tailouts.
- Prepare for Spinner Falls: The best action often occurs during evening spinner falls when adults gather to mate and fall spent on the surface. Use spinner patterns with upright, mottled wings and fish them dead-drift in the surface film.
- Think Movement for Nymphs: Since nymphs are strong swimmers, try swinging a soft-hackle pattern or using a slow retrieve to imitate their natural motion.
Key Fly Patterns
- Gray Drake Nymph: Slim gray body, dark thorax, sizes #12–16
- Speckled Spinner: Gray body with mottled wings, sizes #10–14
- Soft-Hackle Gray Drake: Gray body, partridge hackle, sizes #12–16
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West
Gray Drake Sizes: #8 - #16
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Region: Northwest
Gray Drake Sizes: #8 - #16
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Region: Midwest
Gray Drake Sizes: #8 - #16
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Region: East
Gray Drake Sizes: #8 - #16
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Region: Southeast
Gray Drake Sizes: #8 - #16
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Green Drakes
Common Names: Green Drakes, Western Green Drakes
Identification
- Nymphs: Green Drake nymphs are stocky crawlers with tails that converge into a sharp, pointed appearance. Their robust legs and brown coloration make them easy to identify on the streambed. Typically found in clean, well-oxygenated rivers, their presence often indicates healthy water quality. Effective nymph patterns include bulky, dark brown designs with moderate weight to keep them near the bottom.
- Emergers/Dries: During emergence, Green Drakes transition from olive to grey tones, with stocky bodies and upright wings. Adult Green Drakes are large mayflies, sizes #8–#14, with prominent veined wings and olive or greenish-grey bodies. They are a significant target for trout due to their size and abundance during hatches.
Habitat
- Most Likely: Clean, well-oxygenated rivers with gravel or rocky streambeds
- Occasionally: Spring creeks with steady, cool flows
Seasonality and Hatch Timing
- Hatch Seasons: Late Spring to Early Summer
- Hatch Time of Day: Afternoons and evenings, often peaking under cloudy or overcast conditions
- Water Temperature Range: 50–60°F
Fishing Tips
- Target Crawling Nymphs: Drift Green Drake nymph patterns in moderate riffles or slower runs near the bottom. Use weighted patterns to keep the fly in the strike zone. These nymphs exist year round in the water if green drakes are present.
- Focus on Emergers: Fish emerger patterns in the surface film during the hatch. Trout often key in on struggling Green Drakes as they transition into adults.
- Afternoon Dry Fly Action: Use large Green Drake dry patterns in the late afternoon and evening right into dusk. Present them with a drag-free drift, especially in slower-moving pools or eddies where trout rise to sip adults.
Key Fly Patterns
- Olive Pheasant Tail: Olive or dark olive, weighted with tungsten beadhead, sizes #10–#16
- Green Drake Emerger: Olive body with CDC shuck, sizes #8–#14
- Green Drake Cripple: Olive and grey body with trailing shuck, sizes #10–#14
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West, Northwest, Midwest
Green Drake Sizes: #8 - #14
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Region: East
Green Drake Sizes: #8 - #14
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Quill Gordons
Common Names: Quill Gordon, Early Brown Dun
Identification
- Nymphs: Quill Gordon nymphs are clingers, often found in well-oxygenated riffles and runs. Their dark brown bodies, with subtle grayish-brown tones, make them blend seamlessly into the rocky streambed. Hare’s Ear Nymphs or Pheasant Tails tied in dark brown or black are solid imitations.
- Emergers/Dries: The dun stage features light gray wings with distinct, dark veins and a slender, quill-like brown body. Quill Gordons are one of the first major mayfly hatches of the season, and trout often feed aggressively after a long winter.
Habitat
- Most Likely: Fast-moving, cold streams with rocky bottoms
- Occasionally: Spring creeks with steady flows
Seasonality and Hatch Timing
- Hatch Seasons: Early Spring
- Hatch Time of Day: Late mornings to early afternoons
- Water Temperature Range: 45–55°F
Fishing Tips
- Target Riffles First: Quill Gordon nymphs cling to rocks in riffles, so start with a dead-drifted nymph or soft hackle near the riverbed.
- Look for Slow Transitions: As the hatch intensifies, trout will often move to slower seams or the heads of pools to target emerging duns.
- Use Sparse Patterns: Quill Gordons have slim bodies, so choose flies with a slender, quill-wrapped body for better realism.
Key Fly Patterns
- Quill Gordon Nymph: Dark brown body with a sparse tail, sizes #12–16
- Parachute Quill Gordon: Brown body, gray parachute wing, sizes #12–14
- Soft Hackle Quill Gordon: Brown body with soft hackle for movement, sizes #14–16
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: East, Southeast
Quill Gordon Sizes: #12 - #16
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March Browns
Common Names: Gray Fox, March Browns
March brown nymphs are the reason Hare’s Ears and Pheasant Tail Nymphs are so popular. These tan to brown nymphs display three distinct tails and a slender body that broadens toward the head, featuring prominent legs—a quintessential mayfly profile. Adults respond well to Parachute Adams in tan, gray, or light brown. Though primarily spring emergers, nymphs remain present from January through July.
Identification
- Nymphs: March Brown nymphs are slender with three distinct tails and a body that thickens toward the thorax. Their coloration ranges from tan to brown, making them well-suited for patterns like Hare’s Ear or Pheasant Tail nymphs. These nymphs are common in rivers with moderate currents and are sizes #10–#18, with #12–#16 being most typical.
- Emergers/Dries: Adults are tan, gray, or light brown with upright wings and a delicate profile. Standard dry fly patterns like Comparaduns and Parachute Adams are effective, but specialized patterns that mimic their slightly bulky thorax can be advantageous. Typical adult sizes are #12–#16, with some regional variation.
Habitat
- Most Likely: Rivers and streams with moderate currents, particularly those with gravel or rocky bottoms
- Occasionally: Slow-moving tailwaters with steady flow
Seasonality and Hatch Timing
- Hatch Seasons: Late Winter to Early Summer (January–July as nymphs, April–June for adult hatches)
- Hatch Time of Day: Mornings and evenings
- Water Temperature Range: 50–60°F
Fishing Tips
- Nymphs Year-Round: Drift Hare’s Ear or Pheasant Tail nymphs through riffles and pool transitions. Use a weighted pattern or add split shot to keep your fly close to the bottom, where nymphs are most active.
- Emerger Action: During the hatch, fish emerger patterns just below the surface film. Trout often key in on this vulnerable stage, especially in slower water near eddies.
- Dry Fly Opportunities: Use patterns like the March Brown Comparadun during hatches in the spring. Focus on slower currents where trout rise to feed on adults, and prioritize a drag-free drift for better results.
Key Fly Pattern Characteristics
- March Brown Nymph: Tan or brown body with ribbed thorax, sizes #12–#16
- March Brown Emerger: Tan body with CDC wing, sizes #12–#16
- March Brown Comparadun: Light brown body with upright wing profile, sizes #10–#14
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: West, East
March Brown Sizes: #10 - #14
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Region: Northwest
March Brown Sizes: #10 - #14
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Region: Midwest
March Brown Sizes: #10 - #14
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Cahills
Common Names: Light Cahill, Ginger Quill
Identification
- Nymphs: Light Cahill nymphs are slender with a traditional mayfly appearance, featuring tan, yellow, or brown bodies. These nymphs resemble generalist patterns like Hare’s Ear or Pheasant Tail nymphs, making those flies effective imitations. Sizes typically range from #12 to #18.
- Emergers/Dries: Adult Light Cahills are pale in color, often white, cream, or light tan. Their delicate wings and slender bodies can resemble Callibaetis or PMDs, leading to frequent misidentifications. It’s essential to seine the water and inspect insects closely to distinguish them from similar species. Standard sizes for adults are #12–#18.
Habitat
- Most Likely: Rivers and streams with moderate currents
- Occasionally: Ponds or slower-moving sections of rivers with silt or sandy bottoms
Seasonality and Hatch Timing
- Hatch Seasons: Summer and Fall
- Hatch Time of Day: Sporadic throughout the day, with peaks during mid-morning and late afternoon
- Water Temperature Range: 55–65°F
Fishing Tips
- Generalist Nymph Patterns: Drift Hare’s Ear or Pheasant Tail nymphs through riffles and transitions. Light Cahill nymphs are active throughout the day, making these patterns productive even when no hatch is visible.
- Sporadic Dry Fly Action: During sporadic hatches, use light-colored dry flies like a Light Cahill Comparadun or Sparkle Dun. Focus on slower-moving water or eddies where trout rise to sip adults.
Key Fly Patterns
- Hare’s Ear Nymph: Tan or brown body, ribbed thorax, sizes #12–#16
- Light Cahill Comparadun: Cream or white body with upright wing, sizes #12–#18
- Sparkle Dun Cahill: Light tan body with trailing shuck, sizes #14–#18
Regional Hatch Chart | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Region: East
Light Cahill Sizes: #12 - #20
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Region: Midwest
Light Cahill Sizes: #12 - #20
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Region: Northwest
Light Cahill Sizes: #12 - #20
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Adams
Just to clarify: An Adams is not a species of mayfly. The Parachute Adams is a versatile fly pattern designed to imitate a variety of mayflies. Asking another angler if “the Adams are hatching” will likely get you some puzzled looks—unless, of course, you’re looking to have a little fun.
It’s just a fly pattern. No hatch chart needed for this one—clearly :).
Mayfly spinners
The Big Dance has ended
Mayfly Spinners
Likely 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.
All 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.
Mayfly Spinner Patterns
- BWO Spinner
- Trico Spinner
Conclusion
Lets talk about Caddis
Mayflies are one of the most exciting insects to fish, offering opportunities for both dry fly purists and nymphing anglers throughout the year. From delicate Blue Wing Olives in the winter to giant Hexagenia hatches in the summer, mayflies create some of the most memorable moments in fly fishing. By now, you should have a strong grasp of their life cycle, how to identify them, and the best ways to fish them at each stage. If you’ve ever struggled with picking the right size and color during a hatch, remember that using a seine and paying attention to trout behavior will always lead you in the right direction.
A great tip to keep in mind when fishing mayfly hatches is to go one size smaller than the natural insects you see on the water. Trout can get selective, especially during thick hatches, and a slightly smaller fly often triggers more confident eats. If you’re fishing a spinner fall, make sure your presentation is as delicate as possible—these insects aren’t moving, and any unnatural drift can turn a feeding trout away.
With mayflies covered, it’s time to move on to another trout staple—caddisflies. Unlike the delicate, slow-floating mayfly, caddis are strong fliers and aggressive movers, often skating across the water or tumbling in fast currents. Their erratic behavior makes them an exciting insect to fish, and understanding their unique life cycle will help you make better fly selections and presentations.
Next up, we’ll dive into caddisflies, covering everything from their distinctive case-building larvae to their explosive hatches that drive trout into a feeding frenzy. If you think fishing mayflies is fun, just wait until you see how trout react to an active caddis hatch. Let’s get started.
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Online Entomology Course
- Learn all 23 bugs above and under the water (all stages of each major insect)
- Available On and Offline Through our website and app
- Online = Self-Paced, Unlimited, Lifetime Access
- Useful for anyone who fishes for trout (worldwide)
- Learn how to match any bug to any fly and catch more fish
- Detailed hatch information for mayflies, caddis & stoneflies
- Eight easy to follow lessons to master the knowledge
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The Bugs Covered in Our Entomology Course
Midges
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
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
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.

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

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.
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