Yesterday, I presented a fly pattern with an abdomen created from a piece of twisted, synthetic fibers (Zelon or Antron). The twisting of the fibers and careful wrapping up the shank creates an impression of segmentation. In the below photo, I am showing what I often use, which is a tying thread body with an overlay of wrapped wire ribbing, which also shows segmentation.
What is missing are the fibers that suggest life from dubbing, yarns, ostrich, peacock, pheasant tail etc. Considering that many of these pupa/emerger patterns are tumbling through riffles, it is debatable if it is required. Tie the stiffer patterns like this one and add animation in the thorax. In other patterns add life in the abdomen with materials to suggest gills (like the Fuzzle pattern yesterday). This pattern simply shows the ease of a thread body. The thorax is a little beefy and the thread abdomen could have been tapered larger as it neared the thorax. Still, looks ok. Beard is starling feather barbs and collar is black ostrich. Hook: Size 14. Dubbing: Ice Dub (Peacock)