Philpott described the adults of the species as follows:
♂︎♀︎. 34 mm. Head, thorax, and abdomen whitish-ochreous finely sprinkled with fuscous. Antennae in ♂︎ with rather short pectinations. Forewings triangular, costa strongly arched, sinuate at middle, apex moderately sharp, termen subsinuate, oblique; ochreous-grey-whitish; termen broadly margined with greyish-fuscous; costal edge very narrowly fuscous; a thin curved brown line near base; first line (anterior edge of median band) irregularly subdentate, curved, brown, from 1⁄3 costa to 1⁄3 dorsum; second line (posterior edge of median band) irregular, slight triple projection at middle, excurved beneath, from 2⁄3 costa to 3⁄4 dorsum, brown; an obscure waved pale subterminal line : cilia greyish-ochreous. Hindwings ochreous-grey-whitish; a median fascia and a broad terminal band greyish-fuscous : cilia greyish-ochreous.[4]
Distribution
G. nebulosa is endemic to New Zealand.[2][7] As well as its type locality of Coverham and The Bluff, Clarence River, this species has been found at the Tone River bed and at Ka Whata Tu o Rakihouia Conservation Park in Marlborough. It is also present at Macraes Ponds in Waitaki,[8] and in Otago.[9]
Biology and life cycle
The larvae feed at night.[6] The species is most commonly seen in March.[5]
Host plant
The larvae of G. nebulosa feed on mountain carrot, Gingidia montana.[6][10] This plant suffers from browse reduction which in turn affects the moth population.[11]
^ abcdCraw, R. C. (1987). "Revision of the genus Helastia sensu stricto with description of a new genus (Lepidoptera: Geometridae: Larentiinae)". New Zealand Journal of Zoology. 14 (2): 269–293. doi:10.1080/03014223.1987.10422997.