S3:E34 The Short Happy Life of a Mayfly

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Mayflies are an important food source of trout. The short happy life of a mayfly is about a year – and all but roughly a day or so of its life are spent rolling around the bottom of the river. Their few hours as adults are mostly spent in a mating frenzy, after which the female deposits thousands of eggs into the river. And the cycle begins anew. The variations of mayflies are legion. But there are some basic patterns and types of mayflies that you’ll want to have in your fly box when, uh, opportunity rises. In this episode, we discuss the short happy life of a mayfly – and the happy life of a fly fisher when mayflies emerge.

Listen now to “The Short Happy Life of a Mayfly”

Great Stuff from Our Listeners. At the end of each episode, we often include a feature called “Great Stuff from Our Listeners.” It’s the last segment of each episode, where Steve reads one of the comments from our listeners or readers. We enjoy hearing from you, and appreciate your advice, wisdom, and fly fishing experiences.

How often do you fish mayflies? What is your best story of success fishing a mayfly hatch?


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7 Basic Facts about Mayflies


I don’t always think about mayflies. But when I do, I usually catch more trout.

Here are 7 things you need to know about Ephemeroptera — the insect order popularly known as mayflies. I’ve learned these from my friend, Bob Granger, and from the writings of Dave Hughes and Jim Schollmeyer. The insights have made me a better fly fisher:

1. All but one or two days of a mayfly’s 365-day life span is spent underwater.

This is the nymph stage. No wonder 85% of a trout’s diet comes from beneath the surface. It’s why fishing nymphs is almost always a sure bet.

2. Most mayflies hatch at mid-day.

This means that 11:00 a.m. to 2:00 p.m. is prime time — depending, of course, on wind and water temperature. Overcast, cool days are ideal, especially for Baetis flies and Blue-Winged Olives (BWOs).

3. Mayfly duns ride the surface until their upright wings are dry and hardened for flight.

Duns are the first of two adult forms of the mayfly. Their ride through the current typically lasts for ten to twenty feet. Obviously, this makes the duns vulnerable to rising trout. And these rising trout are vulnerable to your mayfly imitation.

4. If rising trout ignore the mayfly duns on the surface, they are feeding on emergers.

The emerger stage is the brief transition between the nymph stage and the dun stage. The child becomes an adult when the skin splits along the back of the nymph and the winged dun escapes. Wise anglers will put on an emerger pattern in these moments.

5. Once duns turn into spinners, they mate in the air and the females deposit their eggs.

At this point, the females are spent and fall to the water. This creates a “spinner fall” — another opportunity for a trout feeding frenzy. Anglers who see mayflies with flat wings like an airplane rather than with wings sticking up should switch to a spinner pattern.

6. Mayflies vary in size and in the time of year they appear.

In the western rivers, BWOs generally hatch from mid-March through May. Pale Morning Duns (PMDs) are more prominent from May through August. Then BWOs show up in force again in September. Typical sizes range from 14 through 18. But the brown and green Drakes in Henry’s Fork of the Snake River tend to be larger — from size 10 to 12.

7. Mayflies need cold, clean water.

Water pollution makes mayflies disappear. When mayflies disappear, the trout do too. So water conservation is vital to trout fishing.

Interpreting the 4 Feeding Behaviors of Trout

Look at that! Those trout are feeding on duns.”

My buddy Nolan pointed over the starboard bow of our drift boat: “Do you see those fish rising near the bank about forty yards away?”

We were floating the Yellowstone River in Paradise Valley, south of Livingston Montana. It took me a few moments to spot the three trout whose noses kept poking up from the surface. But I didn’t see any tiny mayflies in their dun stage. I thought Nolan was arrogant to make such a claim.

How could he have the 30x vision of a spotting scope?

After I scoffed at him, Nolan explained that he couldn’t see those insects any more than I could. Rather, he made the call by watching how the trout were feeding. While it is not an exact science, you can generally figure out what trout are feeding on by watching their behavior.

1. Noses mean duns

If you see noses poking through the surface, the trout are feeding on mayflies in their dun stage. Sometimes, these trout appear to be standing on their fins, up to their eyeballs in water.

The dun stage is the first of two adult stages of mayflies. A Parachute Adams may work fine. But in some cases — slow, clear water or a specific hatch — it might pay to use a Comparadun or Sparkle Dun pattern. Some kind of cripple pattern may work, too, given that most aquatic insects do not make the transition from nymph to adult stage and remain stuck in the surface film.

2. Fins mean nymphs

If you see only a dorsal fin or tail (and not the trout’s nose), then the trout is feeding on something just below the surface.

This is a good time to use unweighted nymph, which floats just beneath the surface. Or, you can use an emerger pattern which sits low and protrudes into the film beneath it. A pattern which rides high, like a Parachute Adams, will not work well unless it gets water-logged and disappears from your sight.

3. Dimples mean midges or spinners

If you see a small dimple in the water, chances are are the trout are feeding on midges or spent mayfly spinners. You may or may not see the trout’s nose. Sometimes you will even see the trout gently roll through the surface with the grace of a dolphin.

Aside from specific midge patterns, a size #20 Parachute Adams works well for midges. Mayfly spinner patterns have light bodies and wings which lay out to the side (like airplane wings) rather than shooting up from the body at a forty-five degree angle.

4. Splashes mean caddis

If you see rising trout making splashes, they are likely feeding on caddis flies. The reason for the splash is that these flies are fluttering on the surface, and the trout go into attack mode. Some kind of elk hair caddis pattern will do the trick.

Final Thought

Of course, watching surface behavior is only one part of your knowledge base. Knowing which hatches happen in the river you’re fishing at particular times of the year and even specific times of the day is critical to making the correct visual assessment. As always, talk to the experts at your local fly shop or read their reports online. Then keep your eyes open to watch what is happening on the river’s surface.