Thread black (or rust/red for the Redhead version) 12/0
Materials
Bead Black tungsten bead (1.5-2.0mm), optional (1)
Tail Coq de leon or micro fibett fibres (4-6 fibres)
Body/abdomen Thread or fine dubbing (gray, olive, or purple) (as needed)
Rib Fine silver or copper wire (1 strand)
Wing case / head Rust-red thread, dubbing or flash (the 'Darth' trigger) (few turns)
Thorax Dark dubbing (adds a slight bulge) (small pinch)
How to tie it
If using a bead, seat a small black tungsten bead behind the eye; start thread and tie in a short sparse coq de leon tail at the bend.
Tie in the wire rib, then build a slim tapered baetis abdomen of thread or fine dubbing (gray, olive or purple) forward over the back two-thirds.
Counter-rib with the wire in 4-5 open turns for segmentation and durability, then tie off and break the wire.
Dub a small dark thorax, then finish the head with a distinct rust/red trigger. Greg Garcia added the reddish head after throat-samples showed ~80% of the male baetis nymphs had rust-coloured eyes/heads the fish were keying on.
Whip finish and add a drop of head cement (or a spot of UV resin over the head).