... as in Plain Brown Nymph. Those are the smaller of the simple little things in the pic.
I first tied this pattern several years ago but only fished it a few times while still down in SE Idaho.
The past week or so, the fishies on my home water have been actively feeding close to the surface, and while some are willing to come all the way up for a small dry fly, a lot of them are content to wait for whatever it is in the drift that they have been regularly dining on. Enter the PBN. Tied some a couple days ago and had the opportunity to fish them for a while yesterday.
The PBNs in the pic are tied on size 20 Dai-Riki 125 hooks which are a 2X short straight eye emerger style hook. I also tie them on size 18 125s, and that is what I fished yesterday and is shown in the corner of that cutthroat's mouth.
This is a one material fly. CDL fibers from a medium pardo CDL feather.
The tying sequence is - cut a small bundle of fibers from the CDL feather, tie it in at the bend overhanging the bend for a tail / shuck, twist the bundle with hackle pliers or whatever and wrap it forward in touching turns to just behind the eye, tie it off, trim the waste and cut the tying thread.
Some fibers on CDL feathers have a natural taper to them and will create a slightly tapered abdomen and a pronounced thorax - if you are extremely lucky and get just the right fibers. If the fibers you select don't produce that effect, just wrap the fibers back over the thorax area and then forward again to bulk the thorax up.