For the beginning fly tier and fisher, the Pale Morning Dun is a ‘predictable’ hatch on Western rivers from June into September. It is a late morning to early evening window of opportunity for a hatch that has a pronounced pre-hatch nymph ‘drift’ before the emergence on the surface. It is enjoyable to figure out and to fish to. It is one of several Summer hatches that are satisfying to discover and react to.
The ‘crawler’ nymphs will move from the rocks and bottom debris where they have hidden. As they move up out of the protection, toward the surface, they are now at the mercy of the currents and trout. This drift, in moderate to slower waters, can take place over an extended period of time as the nymphs drift, wiggle upward, split their wingcases atop the thorax area, wiggle further toward the surface, shed that nymphal case at the surface (emerge) and poke through the surface film (meniscus) to ‘hatch’. The adults will drift a bit further as those now upright wings (opaque) dry a bit and then they lift off into the air, fluttering and drifting with the breezes of the day, toward shore. (Is that a mega paragraph or what?)
This whole process provides stages of presentation that are satisfying & predictable: nymphs drifting along the bottom in the moderate to slower waters (careful wading, longer distance-stealth presentations?); then emerger/wet fly/flymphs/floating nymphs in the top foot or so of water to the surface; dry fly action and later spinner fall action as the females bob about in quieter side waters to lay eggs and then fall with their clear, spent wings stretched out to the sides like a partially submerged little airplane in film…drifting down in the slower currents.
So many opportunities here for presentations from bottom to top. Once you find a hatch of PMD’s on your favorite stream note its location. Your patterns will tend toward the tan to dark tan (mottled earth tones) in sizes 16-18 over the course of the summer. You can research Google Images for PMD nymphs, emerger, dry and see a large variety of pattern options.