Erechthias externella is a species of moth in the family Tineidae. It was described by Francis Walker in 1864. This species is endemic to New Zealand and is found in the North and South Islands. This species inhabits native scrub. The larvae likely feed on either deceased plant detritus or tough leaves of plants such as palms or flax. Adults are sun-lovers and appear on the wing in October. They actively fly in the afternoon when their movements are rapid and can be hard to follow. They have also been trapped using blacklight.

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