Start black perdigon flat body thread on the size 12 N500 and run a smooth base to the bend. Flat thread lays down without ridges, which matters under a slim dubbed body.
Tie in the silver wire rib at the bend.
Dub a spiky black squirrel body forward to the 70% mark, keeping the dubbing loose so the guard hairs stand out. That spikiness is half the fly. A smooth black body has none of the movement.
Rib forward with silver wire in five or six open turns and tie off, then pick the body out with a needle.
Dub a short, bright red synthetic thorax in front of the body. The black-and-red contrast against the spiky body is exactly what Vasies is after.
Take two turns of grey partridge hackle in front of the thorax, sweep the barbs back and whip finish. Two turns is the limit. More and it stops breathing in the current.
Fish it on the swing across and down, or as a dropper in a team.