The adults of this species prefer open habitat and have mainly been collected on south-facing rocky bluffs.

[4] The exterior surface of the labial palpi of H. extensilis is white-scaled whereas H. polita is dark-scaled.

[4] H. polita also has a transverse white forewing fascia which both H. extensilis and H. frigida lack.

[1] Although larvae of this species have not been conclusively identified, a likely specimen was collected in leaf litter consisting of detritus of Grimmia laevigata.

[3] This species has been classified as having the "At Risk, Naturally Uncommon" conservation status under the New Zealand Threat Classification System.