Mayflies start life as an egg. The egg hatches into the aquatic, immature stage of the insect called a nymph.
Nymph see above
When it’s time for the nymphs to become adults, they congregate in the slow water at the bottom of the river (the cushion). At a predictable time, they ascend to the surface where they encounter the surface film (the meniscus). This is a big deal because the emerging insects (emergers)…
Nymph changing to a dun see above
have to get through the meniscus while escaping their shuck. They are helpless. The trout pick them off as they struggle.
Upon escaping the shuck and getting through the film, the insect becomes a dun.
Dun see above
Duns are sexually immature adult Mayflies. They ride the surface film until their wings dry, then fly to the foliage where their skin dries. It splits open allowing the sexually mature adult to crawl out of the shuck and is now called a spinner see above
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