Helastia siris is a species of moth in the family Geometridae. This species is endemic to New Zealand and is found in the Wellington region as well as on Stephens and the Chatham Islands. It is classified as "At Risk, Relict'" by the Department of Conservation. H. siris inhabits coastal tussock grassland. Little is known of the biology of this species. Adults have been observed on the wing in March and September. Adults are nocturnal and are attracted to light.

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