Hook Standard dry-fly / wide-gap hook, e.g. Tiemco 100 or Fulling Mill All Purpose Dry, #12-16, #12-16
Thread Black 8/0 / 70 denier
Materials
Hook Standard dry-fly hook, Tiemco 100 or equivalent, #12-16 (1)
Thread Black UTC 70 denier (-)
Body/shell Black 2mm closed-cell fly foam, strip cut to ~1.5x the hook gap wide (1 strip)
Body flash/underbody Black Ice Dub or peacock black dubbing (pinch)
Legs Black round rubber legs, fine (or 3 fibers of black Krystal Flash) (3 per side)
Indicator post Hi-viz orange (or fl. pink) 2mm foam tab, or a tuft of fl. orange poly/antron yarn (1 small tab)
How to tie it
Start the black thread behind the eye and lay a smooth thread base back to a point above the barb.
Cut a strip of black 2mm foam about 1.5 hook-gaps wide and 2 shank-lengths long. Tie the rear end of the strip in firmly at the bend so the long tag points back over the tail; keep it on top of the shank.
Dub a slim body of black Ice Dub forward, covering the rear two-thirds of the shank and stopping at the 70% point.
Tie in one strand of fine black rubber leg on each side at the 70% point so a leg sticks out each side (splay them to roughly hook-gap length front and back).
Pull the foam strip forward over the back to form the beetle shell and tie it down at the 70% point with 3-4 firm turns, directly over the leg tie-in.
Set the hi-viz orange foam tab (or a small tuft of fl. orange poly yarn) on top at the tie-down point and lock it with 2-3 turns so it stands up as a sighter. The dark shell hides the fly from the trout while the bright post keeps it visible to you.
Trim the foam shell tag just behind the eye leaving a short black head, whip finish under the front lip of the foam, and trim the legs to length (about one hook-gap each side).