The Pale Morning Dun mayfly is one of the more prettier mayflies we have here in the west, Genus Ephemerlla is a favorite among trout. This is a hatch where an angler can sleep in and have a leisurely breakfast before getting out on the water. PMDs hatch late morning to noon time. These mayflies start hatching as the weather warms in early spring, but on some rivers like the Lower Yuba they begin even earlier due to the lower elevations and the fact that it's a tailwater which can fool the bugs with the rise and fall from water releases. Colors of the dun range from a yellowish olive to light olive, and some have pastels of orange and pink. From the crawler family, these mayflies have three tails and are 7-12mm.
As PMDs get active before the hatch trout will feed heavily on nymphs that let go of the bottom part of the river and become available in the drift. High sticking is very effective during this time but I prefer to swing flies in the tailouts of major runs and riffles. The simple act of your fly rising at the end of the swing mimics the emerging nymphs quite well and aggressive takes are the norm. The nymphs drift to the top water column buoyed by gasses trapped in their exoskeleton upon emergence. To perpetuate the species the PMDs come off in massive numbers at times which can cause quite the feeding frenzy when the trout take notice. Fish can also get fussy at this time but not too selective so an angler will still find it challenging yet fruitful.
The freshly hatched dun is active for two days, then the transformation to spinner takes place in stream side foliage. Spinners have clear wings and a rust colored body, males have over sized orange eyes that attract the female when finding a mate. After mating the male spinners fall to the water and become spent while the female drops her eggs from the air over riffles or by floating on the water. The eggs are yellow in color and some trout key in on females with egg sacs during a spinner fall. The rusty spinner is the standard dry fly to use at this time.
The PMD Sparkle Dun is my go to fly when duns are hatching, refusals are rare with this fly and the trailing shuck lets trout know that this mayfly is a helpless emerger, or even a cripple which translates to an easy meal. Sizes 14 and 16 will cover any hatch you may encounter. Now is the time to spin up some PMD patterns and fill your box with dreams of blanket hatches and rising tout.