Fly Fishing Entomology 101 – The Pale Morning Dun

We were getting ready to step out of the Owyhee River in eastern Oregon and head to our SUV when my son exclaimed, “Dad, there’s one of those pale flies!” He was right. I turned and watched a couple Pale Morning Duns flying near the opposite bank.

It was a late morning in July, and so we tied on a couple of “pale fly” patterns and caught a handful of 16-18 inch browns. Veteran fly fisher Dave Hughes says that Pale Morning Duns are the second most important mayflies for fly fishing — not far behind Blue-Winged Olives.

Here is a quick profile of this species.


  • “Pale Morning Dun” is commonly abbreviated as “PMD.”
  • There are two species of PMDs—inermis (the most numerous species) and infrequens. It is impossible to tell the two apart, but it really doesn’t matter to fly fishers.

The Basics

  • Like Blue Winged Olives, PMDs inhabit all kinds of rivers and streams in the western United States. You will find the heaviest populations in spring creeks and tailwaters.
  • PMD hatches are most prolific in June and July, although they appear in May and continue into August.
  • The best time of day for PMD hatches is late morning to early afternoon. While hatches can begin as early as 9 a.m., PMDs are more likely to emerge around 11 a.m. and continue into the afternoon—until 3 p.m. or so.

Nymph Stage

  • PMDs nymphs belong to the crawler group of mayflies.
  • PMDs in the nymph stage are poor swimmers. They are slow and rather feeble, drifting along the bottom for quite a distance before they reach the surface.
  • PMD nymphs have blocky bodies with a modest taper, and their color ranges from reddish brown to dark brown with a bit of an olive tint.

Adult Stage

  • As their name suggests, Pale Morning Duns have a pale-yellow colored body with yellow-gray (female) or pale gray (male) wings. They also have small hindwings.
  • PMD Duns tend to have trouble getting off the water. So they drift for long distances while their wings dry. Frequently, they get stuck in their shucks as cripples. They often flutter in an attempt to lift off, but then end up back on the surface of the river.
  • Once PMDs emerge and molt into the spinner stage, they mate. Both the spent males and females end up on the water’s surface.

Effective Patterns

  • The classic PMD nymph pattern is a Hare’s Ear in an olive-brown color. A Beadhead Fox Squirrel nymph works too.
  • For an emerger pattern, a PMD Floating Nymph/Emerger is best.
  • For the dun stage, Craig Matthew’s Pale Morning Sparkle Dun is my favorite. A burnt wing pattern (like the one pictured above) usually works well, too.
  • For the spinner stage, try a PMD Parachute Spinner or Pale Morning Quill Spinner.
  • PMD nymphs need to be in the size 16-18 range. PMD Dun and Spinner patterns should range between size 16 and 20.
  • One thing to keep in mind about PMD patterns: they all seem to look different in color, wing type, etc. – depending on the tyer.

Other Entomology 101 Articles & Sources


    Sources: Dave Hughes, Craig Matthews, Jim Schollmeyer

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