Ctenucha rubroscapus, the red-shouldered ctenucha moth, is a moth of the family Erebidae. It was described by Édouard Ménétries in 1857. It is found in western North America, limited to low elevations west of the Cascade Mountains, south of Chehalis in Washington.

The length of the forewings is 19–20 mm.

The larvae feed on Poaceae and Cyperaceae species, including species of the genera Dactylis and Elymus.

...