Helastia mutabilis is a species of moth of the family Geometridae. It is endemic to New Zealand, where it is known from both the North and South Islands. It inhabits native forest at lower altitudes and its larval host are moss species in the genus Racomitrium. This species is nocturnal and is attracted to light. It can easily be confused with the similar in appearance species Helastia alba and Helastia cinerearia.

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