Crystal Flash Red or pearl crystal flash (1 strand)
Superglue or UV resin Clear superglue or uv resin (Thin coat)
How to tie it
Bead an Ahrex FW540 with a red bead and start red tying thread. Red on red on red. A bloodworm is one colour all the way through, so nothing here should break that up.
Tie in a sparse pinch of red marabou at the bend and pinch it to length rather than cutting it, so the tail ends in a soft taper instead of a blunt chop.
As you bind the marabou butts down, keep the body even along the whole shank. Real bloodworms have no taper, so a swollen thorax is the one thing that makes this pattern look wrong.
Tie in a single strand of Crystal Flash right on top, leaving a little hanging off the back so it blends into the marabou tail.
Wrap the Crystal Flash forward in open turns to segment the body, then tie it off and trim. One strand is enough. This is a segmentation cue, not a flash fly.
Whip finish and coat the body with superglue or resin. That coat is what gives the fly the wet, glassy look of a real larva and keeps the marabou underbody from unravelling.