The expansion of the wings is about 1½ inches. The fore-wings are bright green; there are three paler green transverse lines, edged with black; one near the base of the wing, one just beyond the reniform spot, and one close to the termen; this last is inwardly much clouded with dark olive-green; the reniform spot is pale green edged with black. The hind-wings are very broad, pinkish-brown, tinged with green on the termen. In the female the hind-wings are considerably narrower, and are not so strongly tinged with green as in the male.
Some specimens appear to be rather darker than others, but beyond this I have not detected any variation.
The eggs are rather large, globular, flattened above and beneath, and pale green in colour.
The larva feeds on the mahoe (Melicytus ramiflorus).
When first excluded from the egg it is about ⅛ inch long, and of a very pale green colour. After the first moult the caterpillar is bright green, darker towards the head, with white dorsal, subdorsal, and lateral lines; there are eight rows of shining black spots, each spot emitting a number of stout black bristles; the head is yellowish-brown with a few black dots. After the last moult the larva has a totally different appearance. It is pale green marbled with darker green; there is often a whitish lateral line, and an obscure series of diagonal green stripes on the sides of each segment. Sometimes the whole larva has a pinkish-brown tinge, and there are often two or three rows of pale spots. In fact the full-grown caterpillar is very variable in its colouring.
These larvæ hibernate during the winter months, often secreting themselves in the burrows which have been made in the stems of the mahoe by various species of wood-boring insects. They come abroad about the end of August, and are full grown early in October. The pupa state is spent in the earth.
The moth appears in December, January, February, March and April. It is often found at rest on tree-trunks in the daytime, where its beautiful green colouring causes it to resemble, in the closest possible manner, a patch of moss. Mr. Hawthorne tells me that he has frequently found dead specimens in this situation.
This insect is, I think, commoner at slight elevations above the sea-level, forest ranges of from 500 to 1,000 feet in height being apparently the most favourable localities for the species. The appearance of the moth over so long a period would seem to indicate that there are two generations in a year, but I have never found full-grown larvæ in the middle of summer. There is, however, no doubt that the insect passes the winter in the larval condition. This species is often met with very late in the season, frequenting the few remaining blossoms of the white rata until the first or second week in April. Mr. Meyrick thus alludes to the scented tuft of hairs in the male insect: "The large tuft of the fore-wings is the source of a very strong vanilla-like perfume, which scents the box in which the specimens are contained for more than a week after their death; the scent is excited more strongly, even in the dead specimen, by stirring the tuft with a pin."[[17]]
I can fully testify to the accuracy of this interesting observation.