Hans
A thin strip of mole on each side of the underbody of a nymph, then wrapped with small vinyl ribbing creates tiny gills. I have not tied one in some time and the mole skin escaped somewhere in the mass of tying stuff or I would post a photo.

I also use it as tiny zonkers for lake leeches in very basic basic patterns with a tiny tail on very short but heavy "bait" hooks, Mustad 9710 IIRC. Inched slowly along the bottom I have caught some big fish on them. I save pheasant aftershafts for lake leeches and wrap a narrow collar with them on some. The tail and body are moleskin, just like a typical flesh fly, but tiny.
art