In the South Island it is known from the Nelson, Buller, North Canterbury, Otago Lakes and Fiordland regions.

This species has a smaller dwarf form that can be found in the Pouakai Range and at Dart Hut.

[2] The male holotype specimen was collected at Dart Hut in the Mount Aspiring National Park in February by J. S. Dugdale and Kenneth John Fox.

[2] It can be distinguished from its near, and very similar in appearance, relative I. epiastra by the short and blunt frontal protuberances on its head.

[2] In the South Island it is known from the Nelson, Buller, North Canterbury, Otago Lakes and Fiordland regions.