This is a go to nymph that should be in everyone's flybox. I have not found a river that is does not work on. Tie it in a variety of sizes. To me the key is the red thread at the head.
Thread: Red 8/0
Bead: Nickel Tungsten
Tail: Pheasant Tail
Abdomen: Med./ Large pearl Mirage Flash
Thorax: Sow Scud Rainbow Dubbing
Wing Case: Pearl Mirage Flash