This species has occurred at Wellington in the North Island; and in the South Island at Akaroa, Christchurch, and Dunedin.
The expansion of the wings is about 1⅜ inches. The fore-wings of the male vary from pale pinkish-grey to pale greenish-grey; there is an obscure darker basal area, a rather broad central band, formed of numerous shaded, wavy, dark grey lines, which are generally absent towards the middle of the band; there is a black dot above the middle; the termen is shaded with dark grey, and there is an oblique pale mark near the apex. The hind-wings are grey with a few very faint wavy lines. The cilia of all the wings are pinkish-grey. The female is dull yellowish-grey, with the markings very indistinct.
Both sexes vary slightly in the ground colour, and in the intensity of the markings. Mr. Purdie has pointed out that the species is very liable to fade, and hence it appears to vary more than is actually the case.[[33]]
The eggs are oval, pale yellow, changing first to orange, and then to dull grey before hatching. The young larva, when first emerged, is pale greyish-brown and very slender. Later on the caterpillar becomes dull olive-green speckled with black; there are two paler stripes just below the middle of the back, then a fine black line, followed by a very fine white one, then a broad pink stripe on the side; below this is a broad black line followed by a white line and two fine black ones. The larva is moderately stout, and the two prolegs are very close together.
The larva, when full-grown, measures about ¾ inch in length. The general colour is dull reddish-brown, often greenish-tinged. The back and sides are marked with numerous slightly waved fine black lines; there is a double series of black dots down the back, a broad black lateral line, followed by a fine white line. The under side of the larva is pinkish-brown; the head greenish-brown speckled with black. The caterpillar is obscurely marked, and very variable. It is often clouded with greenish colouring.
The food-plant is watercress.
The pupa, which is enclosed in a slight cocoon constructed of earth and silk, is found on the surface of the ground.
The perfect insect is most abundant in December, and is attracted by light. It seems to be about during the entire year, as Mr. Meyrick states that he has taken numerous specimens from May till September, and hence concludes that it is essentially a winter species.[[34]] I can to some extent confirm this observation, as I have also found the insect during the winter, although not commonly. It is probable that there are several broods in the course of a year, and that the species hibernates as an imago.
Regarding the synonymy of this species Mr. Meyrick remarks that "C. ardularia, Gn., is the male and C. inamænaria, Gn., the female of this species. C. subidaria, Gn., quoted by Butler as a synonym, is an Australian species, and not identical."[[35]]
XANTHORHOE OROPHYLA, Meyr.