How to Pick the Right Fly (Part 2): Mayflies 101

16 mins read

This is the second post in our series on how to pick the right fly. To see all the posts in this series, click here

By Spencer Durrant

So, there I was – standing in a river in Oregon with blue-winged olives hatching so thick it looked like it was snowing.

My buddy Ryan and I stared upstream at this huge fish that kept rising, with regularity, to eat a few bugs off the surface with each gulp. The fish was tight up against a chunk of moss, and the current was pushing away from the fish’s lie.

In other words, getting a good drift in such a tight window looked to be as impossible as driving through rush hour traffic without losing a bit of hope for humanity.

Ryan coached me through the cast, then handed me his rod. I was nervous – I didn’t want to screw up this up.

By a stroke of luck, I made a perfect cast. The fly drifted right into the fish’s kitchen. The trout rose, I set the hook, and a few minutes later I let a 22 inch brown swim back to its home.

close up shot of a brown trout half in and out of the water in an angler's hand.

Making that cast was lucky, but fishing with Ryan that day was even luckier. He spent all of that epic blue-winged olive hatch teaching me about mayflies. By the day’s end, I felt confident enough to go fish a mayfly hatch all on my own.

That’s what I want to give you in this post – the actionable knowledge you need to feel as confident as I did, so you can go have success fishing with mayflies. From identifying mayflies at their individual stages, to picking flies to match any phase of the hatch in which you find yourself, this post is a crash course on all things mayflies.

What is a mayfly?

Mayflies are aquatic insects, found in just about every trout river in the world. All told, there are over 3,000 species of mayflies.

Thankfully, we don’t need to memorize every species. As anglers, we’re concerned with just a few of them:

Now, that might feel like a lot – like I’m asking you to find a polite driver from Utah – but I promise it’s not. Stick with this post and you’ll be able to spot a blue-winged olive as easily as you can spot a tourist on your home water.

Mayfly Life Cycle

Before we get into the details of the bugs themselves, we need to learn about the life cycle of a mayfly.

Even with the huge diversity of species, mayflies all follow the same general life cycle. They begin as a nymph, become an emerger, hatching into the adult – or dun – version of the aquatic insect, before mating and falling, spent-winged, back to the water.

mayfly life cycle graphic that depicts a mayfly going from an egg to an adult.

Now, the ability to tell if fish are eating the emerger or the dun can make or break your success during a mayfly hatch. This skill is absolutely vital, but fairly easy to master. We will cover that more in a minute.

graphic of a mayfly nymph and mayfly adult, with bullet points describing important aspects of each insect.

Adult mayflies are characterized by their long, slender segmented bodies, upright wings, and forked tails. The nymph versions of mayflies are short, dark bugs with three pairs of legs, a segmented body, and clearly forked tail. They come in a variety of sizes and colors, all the way from a size 8 down to a size 26.

Identifying Hatch Stages

As mayflies emerge from nymph to dun (adult), their movements attract trout. Trout key in on the stage of the hatch that’s the easiest for them to eat while expending the least amount of energy. Often, even when it appears that there are only duns on the water, trout are picking off straggling emergers or cripples. Emerging and crippled bugs are easier to eat, since they can’t escape as quickly as a dun can. That makes them a high-value food target for trout.

The key to knowing what stage of the hatch trout are keyed in on is knowing what rise forms look like.

A rise form is the disturbance a fish makes when it rises to eat a dry fly. Depending on what they’re eating, trout create different rise forms.

Learning to recognize these rise forms will tell you, within just a few minutes, what fish are keyed in on.

graphic depicting how a trout looks when it breaks the water to eat an emerging insect vs an adult insect.

Emerger Rises

Trout eating emergers create a unique rise form. Instead of seeing a fish’s head when it eats, you only see the back and tail fin. This happens because fish are eating bugs as they travel to the surface or are stuck in the surface film – emergers and cripples.

close up shot of a brown trout rising to eat a mayfly off the river's surface

A crippled mayfly is exactly what it sounds like. It’s either a dun or emerger that has some sort of crippling deformity that prevents it from leaving the water’s surface.

Dun Rises

When trout eat duns, they create the classic dry fly rise form. Their head breaks the surface, leaving behind the “ring of the rise” we’re so familiar with.

close up shot of a brown trout rising to eat a mayfly off the top of a river

Trout also eat spinners or spent-wings with a rise that looks like a dun rise. Spinners and spent-wings are two names for the same fly – the dead or dying mayfly that’s finished mating and “spins” back down to the water’s surface.

Major Mayfly Types

With over 3,000 mayfly species on the planet, learning to recognize them all is an impossible task. On top of that, there are over 150 species of blue-winged olives! Thankfully, we don’t have to memorize each species of each type of mayfly. The old joke about a guy on a river in a tweed jacket, smoking a pipe, and calling mayflies by their Latin names exists for a reason – anglers like that are real. I’ve met them.

You don’t need to be that angler. Thank goodness.

You do need enough actionable information, though, to identify bugs and pick a fly that matches what fish are eating. To that end, you should focus on knowing these mayflies in particular:

  • Blue-winged olives (BWOs)
  • Pale morning duns (PMDs)
  • Drakes
  • Tricos
  • Callibaetis

Let’s take a look at these bugs in greater detail.

Blue-winged Olives (BWOs)

Blue-winged olives (BWOs) are one of the most easily recognizable mayflies. Anglers look forward to the fall and spring hatches of BWOs because these bugs hatch thick enough to bring trout of all sizes to the surface – even big ones.

Recognizing BWOs

close up shot of a blue winged olive mayfly on a black background

Blue-winged olives are the first and last mayflies to hatch each year. Early spring and late fall are typically when BWOs hatch in earnest. Spring BWOs come off from April through May, and fall BWOs hatch during September and October.

However, some mayflies hatch during the same time as BWOs. To tell them apart, remember that BWOs have the following features:

  • Dark to light olive colored bodies
  • Smaller in size, around 16 for a dun. Occasionally as large as a size 14
  • Light blue wings

blue-winged olive mayfly hatch chart that depicts when these bugs are most active for anglers

The patterns I’d recommend most for fishing a BWO hatch include:

We have multiple BWO patterns in our BWO Baker’s Dozen pack.

Pale Morning Duns (PMDs)

Pale morning duns are, for me, the sign that summer is officially here. They begin hatching in earnest in June, and continue throughout the summer. Some of my best fishing is during PMD hatches on tailwaters.

Recognizing PMDs

close up of a pale morning dun mayfly on a black background

The PMD hatch overlaps with brown and green Drakes, so you’ll likely see some PMDs mixing with those bugs. Luckily, PMDs are easy to identify. They have the following features:

  • Light-yellow colored body
  • Usually larger than BWOs, often a 14
  • Clear, gray wings

graphic of a pale morning dun hatch chart

The patterns I’d most recommend for a PMD hatch are:

You can find some of our favorite PMD patterns in our PMD Baker’s Dozen pack.


Drakes are among the biggest mayflies, which makes them a special treat for trout. Some of the biggest fish you’ll catch all year will likely come during a Drake hatch. Drakes are among the first big flies to hatch, and they come off right before, or during, runoff. That combines to make them an easy, must-have meal for trout just waking up from a long winter. Drakes come in two general varieties, for angling purposes – green and brown. Green Drakes hatch in mid-May through June, and Brown Drakes hatch immediately after the Green Drakes.

Recognizing Drakes

close up of two images side by side of a green drake and brown drake mayfly

Since Drakes are such large flies, they’re easier to spot and identify. Green Drakes, as their name implies, have a vibrant green body, while Brown Drakes have an earthy brown body.

  • Green body for Green Drakes, brown body for Brown Drakes
  • Long, segmented body
  • Large – up to a size 8

graphic of a green drake hatch chart

graphic of a brown drake hatch chart

The flies I’d recommend most for fishing either a brown or green Drake hatch are:

You can view the Drake Baker’s Dozen pack here.


A trico is an extremely small mayfly that hatches in huge numbers. They’re common on tailwaters, and trout love them because tricos can’t escape as quickly as other, larger mayflies can. Tricos hatch later in the summer, starting in July and going through August.

Recognizing Tricos

Tricos can come in a variety of colors, but they’re always small, and always have three tails. While small, they still maintain the classic mayfly body shape. Remember that tricos hatch in July through August. This is outside the window of other mayflies, and most midges. So, if you see small flies buzzing around the water’s surface that time of year – and you observe trout eating them – it’s a safe bet those flies are tricos.

  • Dark colored body, usually black, brown, or green
  • Extremely small – size 18 to 26
  • Classic mayfly shape

graphic of a trico hatch chart

Some flies I’d recommend to have along during a trico hatch:

We have parachute tricos in this Baker’s Dozen pack of flies.


This mayfly hatches in stillwater environments (lakes and ponds), and is one of the most exciting hatches you’ll ever fish. Callibaetis mayflies hatch in large blankets, which causes the trout to eat without any care in the world. They’ll often rise for callibaetis flies in a straight line, making casting for these hungry fish an easy task of placing your fly just ahead of the trout. This hatch occurs during May all the way through August.

Recognizing callibaetis

close up shot of a callibaetis mayfly on a black background

These are larger mayflies with pale, earth-tone bodies. They have exceptionally thin bodies, but otherwise have the classic mayfly profile.

  • Larger, sizes 12 – 16
  • Earth-tone color
  • Thin, slender bodies

graphic of a callibaetis mayfly hatch chart

The flies I’d recommend you have along for a callibaetis hatch include:

  • Parachute Adams – a classic fly that still slays today
  • Light Cahill – great for the smaller, lighter callibaetis hatches later in the summer

You can find all of our callibaetis patterns in this Baker’s Dozen pack.


Here are all the hatch charts put together. Take a screenshot to use as a tool during mayfly season.

blue-winged olive mayfly hatch chart that depicts when these bugs are most active for anglers


Keep on Learning

So, that was a lot of information. If your brain hurts, that’s totally normal. Grab your favorite beverage, bookmark this page, and return to it as often as you need until you feel you’ve grasped the info.

Oh, and keep tabs here on the VFC blog, too. Our next post in this series on choosing flies is all about caddisflies – the buffalo wings of the aquatic insect world. All the trout love ’em, but some really want the boneless garlic parmesan instead of the atomic ghost pepper. In other words, there’s some variety to caddisflies, and we’ll cover all that in the next post in this series!


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