Tie in a clump of black deer hair at the bend with the tips pointing back over the bend. Bind the butts down along the shank.
Wrap a small body of peacock herl or black dubbing forward to the 80% mark, modest, not fat. The shellback will define the profile.
Pull the deer hair forward over the top of the body as a shellback and tie down at the head. Pull firmly so the hair rounds over the body like a beetle's wing case.
Trim the hair butts, leaving a short stub as a small head.
Tie a tiny dot of bright foam or yarn on top. This is non-negotiable, a black beetle flush in the film is invisible without it.
Optional: 2-3 sparse hackle fibers or rubber legs out each side.