Hydriomena arida

This species was first described by Arthur Gardiner Butler in 1879 using specimens collected by Frederick Wollaston Hutton in Dunedin and named Melanthia arida.^[4][2] In 1883 Edward Meyrick, thinking he was describing a new species, named this species as Cidaria chaotica.^[5][6] Meyrick synonymised this name into Cidaria arida in 1884.^[7][8] George Hudson discussed and illustrated this species under the name Hydriomena arida in both his 1898 book New Zealand moths and butterflies (Macro-lepidoptera) and his 1928 book The butterflies and moths of New Zealand.^[9][10] It has been hypothesised that species belongs to another genus and so this species is also currently known as Hydriomena (s.l.) arida.^[11] In 1971 John S. Dugdale suggested this species may fall within the genus Cephalissa but in 1988 kept the current placement of this species.^[12][2] The male holotype specimen is held at the Natural History Museum, London.^[2]

Hudson described this species as follows:

The expansion of the wings is 1+1⁄8 inches. The fore-wings are dark blackish-grey; there are two small cream-coloured patches on the costa at 1⁄3 and 2⁄3 continued across the wing as two curved series of small cream-coloured spots; there is a subterminal series of whitish dots. In most specimens there is a very broad paler brown median band with a rounded projection below the middle almost touching the termen; this band is traversed by numerous fine wavy dark brown transverse lines and contains a conspicuous discal dot. The hind-wings are very pale brownish-grey or creamy-grey; all the cilia are nearly black.^[10]

This species is variable in appearance. Hudson goes on to say that this species can be distinguished from similar appearing species as its forewings are very darkly coloured but have a broad often paler median band.^[10]

This species is endemic to New Zealand.^[11] This species occurs in the South and Stewart Islands.^[10][13] A specimen has also been collected from Arapawa Island in the Marlborough Sounds in July.^[14] This species is regarded as being rare. In 1988 it was reported as being locally extinct in Dunedin.^[2] However in February 2022 a specimen was observed in Port Chalmers.^[15]

This species inhabits native forest and has been found at altitudes of between 1500 and 3000 ft.^[10] The larval host of this species is Gunnera monoica.^[3][16]

The adults of this species are on the wing most commonly from October until February and attracted to light.^[3][13]