Start black 70-denier thread on the front third of a size 16 curved scud hook; do not run it down the shank yet.
Cut a strip of 2mm black foam slightly wider than it is thick and snip a point on one end. Catch that point in so the body will reach almost level with the hook point, a couple of wraps to stop it spinning, then a few more to bury the tie-in.
Push the foam up out of the way and take the thread in touching turns well around the bend; rotate the hook in the vise if you need to.
Bind the foam down at the rear with one medium wrap, another, then a few tight wraps. This sets the back of the body.
Spiral the thread forward over the foam in two or three tight bands to compress the underbody into segments; this thins the underbody rather than decorating it.
Return the thread to the front of the underbody, fold the foam forward over the top, and pull it fairly tight so it sits low like a caddis, not humped like a beetle. Lock with a couple of tight turns, snip the tag as close as you can, and bind the stub flat with as few wraps as will hold.
Optional indicator: leave the thread slightly forward, slip a strand of white parapost under it, pull both ends back, and wrap the thread back over it to the body.
Tie in a small dry-fly hackle by a stripped stem, concave side toward the hook, and trim the excess stem.
Optional head: dub a short, thin noodle of black rabbit and wind it at the head.
Wind the hackle about four turns with hackle pliers, back the thread off one turn, take two wraps to secure, ramp a small head back just enough for a whip finish, and snip the hackle tip.
Whip finish, trim the indicator shorter than the hackle tips, and add a drop of head cement.