First of your rods and nets are works of art. I am saving my pennies for a bamboo rod.
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I have understood that after emerging, the insect sitting on the water is a dun. They are waiting for heir wings to dry off, or the rest of their shuck to come off, or have some kind of retardation and become cripples.
If they are lucky enough to make it without being eaten, they turn into duns to mate. I have been taught that they go through a color change and their wings turn white or clear. They fly off into the air to do their thing. The females return to the water to lay eggs and then die. The males die after mating and create the spinner fall.
I will use tricos as my example. For a trico dun I would tie three microfibbet split tails, black dubbed body with light or dark dun colored hackle. For a cripple I use white Widows Web with a black body and light or dark dun colored hackle. All tied in sizes 20-26.
For spinners I tie females a glossy dark green with three microfibbet tails and white hackle. I sometimes put a small (very small) dubbing ball on the back end as an eggs sack. Usually light yellow or cream colored. For spinner males I use three microfibbet tails, black body, and white fluro fibre wings tied straight out from the body so they lay flat on the waters surface.
Hope my examples help