A Bead Head Pupa pattern. I used two different colored pieces of copper wiring wrapped over the simple thread body. Contrast, segmentation and weight. The busy hackle and thorax materials (Ice Dub, ostrich and partridge) add to the suggestion of life.
An even simpler fly, equally dense to quickly sink. Copper wire tied in at the front of the shank and closely wrapped toward the end then used to rib forward over the wire abdomen. The dubbing ball for the thorax hides the tie in point for the copper wire.