Cromarcha stroudagnesia is a species of snout moth. It was described by Solis in 2003 and is endemic to Costa Rica. The length of the forewings is 8–10 millimetres (0.31–0.39 in) for females and 5–9 millimetres (0.20–0.35 in) for males. There are two forms, with either a white or light brown ground colour. In both forms, the antemedial and postmedial lines are prominent. Both the upper- and underside of the hindwings have dark brown scales. There are two successive generations, one beginning in May and one in September.