delfame,
A soft hackle. Here's a pic of a size 16. This is the fly "off the bench". if I want to specifically fish pupae, I pull some dubbing out between the ribbing stream side.
I fish it deep with a weighted nymph, in the film or greased on the surface. When fishing greased on the surface, I clip the hackle on the bottom of the fly stream side and grease the top hackle only. Heck, I've never done it, but it could be converted to the larva by trimming the hackle off.
I build up an obvious head with the brown thead, wrapped over the area where the hackle stem was wrapped. This binds down the fibers with thread to make it more durable and allows the hackle to "hug" the body rather than flare outwards.
this version is tied with mottled hen, but for others I use dark partridge- never light partridge. Grouse is another alternative.
In this version I tied a few 3-4 strands of antron like an underwing, extending past the hook bend.
pretty simple, easy to tie and very effective
oh two more details. I pulled the hackle aside a bit so that the body is more visible for the picture. They tend to have a near equal distribution of hackle fibers around the body. It is ribbed with gold wire, the pic doesn't show that well