Gadira petraula

This species was first described by Edward Meyrick in 1882 using specimens he collected on the Lyttleton Hills and named Scenoploca petraula.[1][2] In 1883 Meyrick gave a much more detailed description of the species.[3] George Hudson discussed and illustrated this species under that same name in his 1928 publication The Butterflies and Moths of New Zealand.[4] In 1973 David Edward Gaskin placed this species within the genus Gadira.[5] The lectotype specimen is held at the Natural History Museum, London.[2]

Illustration of G. petraula by George Hudson.

Meyrick described the larvae of this species as follows:

Larva moderately stout, cylindrical, wrinkled, very sluggish ; rather dark greyish-fuscous on back, much lighter on sides; spots minute, blackish, obscure ; head fuscous.[3]

Hudson described the adult moths of the species as follows:

The expansion of the wings of the male is slightly over 5⁄8 inch, of the female about 1⁄2 inch. The fore-wings of the male are rather elongate, triangular, with the termen oblique; white with blackish-grey markings and very slightly tinged with ocherous; there is an irregular basal patch; a broad curved band preceding the first line and a narrow band following it; a large irregular discal patch, darker on the costa, surrounding a single, clear white, reniform spot; a conspicuous black sub-apical patch, and two wavy blackish transverse lines, indicating the position of the second line; a series of blackish terminal dots. The hind-wings are pale grey. The female has the fore-wings very narrow oblong and the hind-wings proportionately shorter and rounded; the markings resemble those in the male but are cramped and obscured.[4]

The adults of this species are very similar to that of Gadira leucophthalma however G. petraula is slightly smaller and their forewing dorsum has a grey and black pattern in contrast to the more whitish grey in G. leucophthalma.[6] Another distinguishing feature is that the female of G. petraula is short winged.[6]

This species is endemic to New Zealand.[7][8] This species is only known from Mid Canterbury.[9] The record of this species from Stephens Island is as a result of a misidentification and the record from Australia likely results from Meyrick gifting one of his New Zealand specimens to an Australian collector.[9]

The adult female of this species is flightless.[3] The males have been recorded on the wing in March.[4] Adults have also been found mid October to up to December depending on the altitude of the habitat in which the moths live.[6] It has been hypothesised that there are likely a succession of generations of the moth within a calendar year.[10]

Lyttelton hills, type locality of G. petraula.

The larvae of G. petraula feed on moss or lichens growing on volcanic rocks.[11][10] They live in crevices, creating a shelter of silk from which they emerge to feed.[4] This species preferred habitat is coastal, montane, and low alpine rocky sites.[6]

This species has been classified as having the "At Risk, Naturally Uncommon" conservation status under the New Zealand Threat Classification System.[12][6] Both the habitat and type locality of this species is at risk due to urbanisation.[9][10] The 2010-2011 Christchurch earthquakes destroyed or damaged much of this species habitat.[6] Another threat is the cleaning of rock faces by rock climbers.[10]

Wikimedia Commons has media related to Gadira petraula.

• Image of larva webbing