Scoparia declivis was described by Alfred Philpott in 1918. However the placement of this species within the genus Scoparia is in doubt. As a result, this species has also been referred to as Scoparia (s.l.) declivis.
The wingspan is 28–32 mm. The forewings are fuscous-brown, irrorated with white. The basal area is pale up to the first line. This first line is whitish. The hindwings are pale whitish-ochreous. Adults have been recorded on wing in February.