The Isonychia is a decent sized mayfly that can be so numerous at times, you simply aren’t sure where to cast. There have been plenty of times at dusk where I see more trout taking emergers than I do the mayflies that are aimlessly drifting on the surface, when the hatch is in full swing. Some trout will even come barreling our of the water to take them as they rise and swim through the water column.
Some of them do make it, and the evidence can be found strewn all around the river bank where they had once climbed up onto the rocks to finish their transformation.

The next time you’re in the middle of an Isonychia hatch; try to divert your eyes away from the far bank for a few seconds, and look down. Concentrate on what is right in front of you at your feet. If you stand still, gazing into the water as it swiftly passes, you will see the nymphs. They are almost breaking dancing as they head down river! Many of them do not make it to adulthood, they become stuck in the film.
That is where this pattern comes in handy, and its for two reasons. When dead drifted tied just the way it is, it gives a little movement. A little extra attention grabber as it passes the eye of a hungry trout. Then after the fish have destroyed it to the point that your CDC bubble is ruined? Let it sink and swing it! It will wiggle and thrash around with those broken CDC fibers and continue to work.