THE PALE MORNING DUN FLY PATTERN (PMD)
The PMD is a small mayfly found in most western North American trout streams and other locations throughout the world. On most days during the emergence period you can practically set your watch by the start and stop times of the hatch. On some rivers the hatch lasts for months. This gives the trout time to tune into this abundant food source at all the different stages; nymph, emerger, dun and spinner. There body size ranges from 6mm to 9mm in length which corresponds to size 14 to 18. Like other mayflies they get smaller as the season progresses. This phenomena lead to confusion in identification of species by the early angling entomologists, along with the even more confusing different body shades of the females and males which did not help classification. Body colours range from pale yellow olive, pale chartreuse to rusty orange.
'Pale Morning Dun' is a common term for different species of the insect family group called Ephemerella. It is hard to tell them apart without the help of a microscope. For the fly fisher it does not matter what sub species is hatching. In appearance, behavior and habitat they are so much alike. The PMD nymphs are crawlers. They live among rocks and debris feeding on vegetation. They have well developed legs that enable them to crawl along the bottom of the river without getting swept away. They stay hidden among the rocks and debris and are seldom available to the trout. They are not very good swimmers. If they do lose contact with the river bottom they can drift for long distances before sinking to the bottom again. They are very vulnerable if this happens. They have square shaped head and rectangular body. A Gold Ribbed Hairs Ear Nymph or Pheasant Tail Nymph is ideal as a PMD nymph imitation.