Mount the curved hook, tie in a strip of clear Scud Back and the wire rib at the bend, plus a few short hackle fibers as a tail.
Dub a full body of guard-hair-rich dubbing around the curve, plumper than a mayfly nymph.
Pull the shellback over the top and tie down at the head.
Counter-wrap the wire rib in 5-6 turns, segmenting the shell.
Pick out the belly dubbing hard. Those trailing fibers are the scud's many swimming legs.
Whip finish.
Substitutions
Body instead of Dubbing with guard hairs: Sow Scud dubbing (olive) — Purpose-made, coarse fibers; Squirrel dubbing (olive) — Natural, spiky; Arizona Simi Seal (olive) — Coarse with flash
Shellback instead of Clear plastic or Scud Back: Clear Scud Back — Standard material, easy to find; Thin Skin (clear) — More durable; Clear stretch tubing — Budget alternative
Rib instead of Fine wire: Clear mono — Invisible segmentation; Fine copper wire — Adds slight flash