This species is endemic to New Zealand and occurs in the Buller, Marlborough, North and Mid Canterbury regions.This species inhabits short tussock grassland in montane to subalpine zones.

Lewis at Broken River, Canterbury and named Hydriomena expolita.

[3][4] George Hudson discussed and illustrated this species in his 1928 book The Butterflies and Moths of New Zealand under the same name.

Forewings moderate, triangular, costa moderately arched, apex subacute, termen sinuate, oblique; whitish-grey with faint purplish tinge; markings dark purplish-fuscous; basal line thick, evenly curved, projecting angularly at middle; anterior margin of median band inwardly oblique beneath costa at 1⁄3, thence broadly excurved to dorsum at 1⁄4; posterior margin from 2⁄3 costa to 3⁄4 dorsum, with strong broad apically-indented projection at middle; traces of a thin waved white subterminal line; an oblique suffused purplish-fuscous fascia from apex : cilia grey, obscurely barred with fuscous, tips whitish.

[2] This species prefers short tussock grassland habitat in montane to subalpine zones.

[9] This moth is classified under the New Zealand Threat Classification system as being "At Risk, Relict".