One of the great hatches of the West, pale morning duns have everything going for them: massive numbers that trigger aggressive surface feeding.
The PMD Dun works very well in West Yellowstone, Montana and near Mammoth Lakes area in California.This small, pale-yellow mayfly of the crawler group is often referred to by its initials, PMD. Despite the name, hatches can occur in the morning, early afternoon, or evening. It's not unusual to have both morning and evening emergences on the same day. The hatch season begins as early as June and lasts as late as September, depending on the stream. This is often the dominant hatch where and when it occurs.