Start UTC 70 black at the front of a size 10 scud hook and tie in the gills. Take a four-strand braided midge gill and peel it down to two strands. A real chironomid has two tufts at the head, so two strands wet out into exactly the right look.
Whip finish, slide a 2.8mm black bead up over the gill wraps, reattach the thread and start building the taper.
Tie small red wire in on the near side and run it into the bend, keeping the thread smooth both directions. Always be working the taper as you travel up and down the shank. That habit is what makes chironomids look right.
Tie in gunmetal grey Flashabou and bind it evenly along the shank, keeping the materials evenly distributed so no lump forms on one side.
Wrap the Flashabou forward in touching turns with no gaps, up to the bead, and tie it off. Gunmetal grey is hard to find but worth chasing. It matches an enormous number of chironomids.
Rib the red wire forward with a couple of turns right at the bottom to leave a small red tag, then seven even wraps up the body. The red tag at the tail is the blood spot the trout look for.
Counter-spin the bobbin to flatten the thread before whip finishing so the collar stays smooth, brush the gills together and trim, then coat with superglue for durability.