All these crazy terms used in fly fishing. No wonder less people are flinging flies every year. This article is going to simplify one of those mystery terms.

What is a DUN in fly fishing?

A fly fishing DUN is the stage of the mayfly between a nymph and adult mayfly. The technical term is the SUBIMAGIO stage. This is a vulnerable phase for the mayfly since the wings are formed, but have a dull opaque color. Often this stage results in trout actively feeding from the water surface.

Sulphur Dun for Fly Fishing
Sulphur Dun for Fly Fishing

Other DUN terms in fly fishing

I like the word molting when the dun stage is discussed. Those little guys have popped onto the surface and the wings are unfolding and they transform in color from the darker nymph to a lighter shade of the adult colors. 

I’ve heard the term DUN relative to the color of a fly. A DUN color is usually a brown gray or a gray mixed with a blue. A weird thing is one of the most popular DUN patterns is the PALE MORNING DUN which is typically a yellow and white. 

In fly tying the term DUN hackle is sometimes used to indicate the wrapping forming the body of a fly. Think of the feathers wrapped up the body of a wooly bugger (palmered) or the wrap found just behind the head of a fly.

Can You Have a DUN Hatch?

Heck yes, the dun is a stage of a mayfly hatch. In fact, when you see fish taking flies off the surface of water it’s usually during the DUN phase when the bugs are vulnerable on the water. Remember the mayflies are morphing into an adult, the wings are still forming.

Where does a DUN fit into the stages of a May Fly?

may fly stages
may fly stages
  1. Egg Stage, mayflies can lay 1000s of eggs. Trout don’t actively feed on mayfly eggs, but the dropping of the eggs on the water can cause trout to rise.
  2. Nymph Stage, yup those ugly squirmy aquatic bugs crawling around on the river or lake bottom. Check out this link to WIKIPEDIA MAYFLYS
  3. Dun or Subimago stage, the mayfly has molted from the nymph and now has wings. Often the wings are still developing and will have the gray coloring.
  4. Adult or Imago stage, this is when the mayfly is sexually mature. At the Imago stage the mayfly may only live for 24 hours.
    May Fly Stage Cycle Sketch

Popular DUN Flies used in fly fishing

  • Mahogany Dun, a common may fly that has prolific hatches in the spring. A go to fly for many pieces of river. The size 12 and red/brown color are a great fly for matching many hatches.
  • Comparadun, marked by the upright wings bending toward the head. A great fly in the size 12 to 16. Usually the wings are a lighter color making these flies easy to see.
  • Sulfur, usually the bright yellow is a dead give away for this fly. Look for hatches in the spring May and sometimes even early June. Watch for these pretty’s in the morning.
  • Blue Wing Olive, a favorite winter time fly when the sun pops out in the afternoon. Size 14 to 18 is good, look for those sunny patches of water from September to April.

When to fly fish with a DUN fly

Dry fly fishing revolves around observing trout taking flies from the surface of the water. Most time this is during that two-hour span at sunrise and sunset. I like to think about those transition times as the magic time.
Often if a prolific hatch is happening

How to Setup a Fly Rod to Fish with Dry Fly Duns

For dry fly Dun fishing think about a lighter rod. A 3 weight 9 foot fly rod, I really can’t say enough good stuff about the TFO Drift  (Link to read more about the drift) which comfortable casts a 4 weight forward floating line.

To that fly line add a 9-foot tapered leader in a size 5X. From there attach 12 to 18 inches of 5X or 6X tippet. Read about recommended Tippet in this article How to select a Tippet Length and Size. 

I enjoy a medium action graphite or even a fiberglass fly rod. That gentle motion can put you into that relaxing mood that is associated with fly fishing.  For more information on relaxation read  Is Fly Fishing Relaxing

Where to use Duns in a River

Learning to read the water will help increase you hook up percentages. Trout are typically found in cool flowing rivers that have varying gradients.

Rivers sometimes follow a Riffle-Run-Pool sequence. When the gradient increases the water will push and pile rocks into the Riffles.  After the riffle a Run will focus the water.

This Run area is where you should be fishing dry fly duns. The nymphs dislodge from the rocks in the riffle and hatch in the runs.

After the run is usually a Pool with slower deeper water. Trout can be found here but in lower numbers.

5 Tips for fly fishing a DUN

  1. Often during a large hatch your fly is just another of the thousands floating by a hunger trout. When this happens, change things up a little. Example bump up the size of the fly your using or even cut back the hackle to cripple the fly.
  2. Timing and observation, I’ll bet you eat dinner on a schedule. Trout do the same thing, so watch a rising fish and count off the rhythm in your head.
  3. If your floating in a boat and see a rise rising ahead, STOP and give yourself time to make the right cast to the rising fish.
  4. The big switch, if you’ve tied on 7 flies with no results switch things up big. I’ve often switched to a DRY-Dropper setup at these times. Read about the Dry/Dropper Setup Here.
  5. Duns will float in water lanes close to the bank. You might lose some flies getting caught in the stream side brush, cast into those areas.  When the right cast + a good drift + fishy water come together it’s truly like magic watching a trout rise.

It’s All About the Natural DRIFT

It’s been said so much that I hate repeating this. When dry fly fishing the natural drift is what its all about. Positioning for a good cast, with no drag when drifting through those fishy waters is key.

It takes time on the water to hone these skills. So, get out to a river and observe. Watch how the bubble lines move at different speeds. Watch how the water flows around a boulder and creates slack water directly behind it.
Learning how to position yourself and for the best cast in those situations is what makes fly fishing fun.