This is an extremely variable insect. In some specimens there are very extensive white patches on the wings, whilst in others the colouring is almost uniform rich brown, and the characteristic markings can only be detected with difficulty. It may, however, be distinguished from the allied species by the interrupted pale jagged transverse line near the termen and by the absence of greenish colouring.
The eggs are oval with the surface honeycombed; they are pale green in colour.
The young larva, when first hatched, is much attenuated, light reddish-brown with a broad pale lateral stripe, and a few bristles. The full-grown larva measures about 1½ inches in length; it is rather slender and has a large hump on the sixth segment. Its colour is dark reddish-brown, mottled and striped with dull white and greenish.
It feeds on the white rata (Metrosideros scandens). During the day it firmly grasps a stem of its food-plant with its prolegs, holding the rest of its body out from the branch in a perfectly straight and rigid position. When in this attitude it so exactly resembles a twig, that, even in the case of captive specimens, it is often a matter of the greatest difficulty to find a caterpillar amongst the branches. Several times I have even caught hold of a larva, thinking it to be a twig, so perfect is the resemblance. At night these larvæ become much more active, and by the aid of a lantern they may then be seen busily walking about and feeding.
The pupa is enclosed in a slight cocoon about two inches below the surface of the earth. The larvæ of the autumnal brood remain in this condition during the winter, but in the case of the spring and summer broods the pupa state only occupies a few weeks.
The moth appears from November till May. It is very common in forest regions, and may be observed resting on the trunks of the trees, its pale yellow hind-wings being completely concealed by the mottled brown fore-wings. In this position the insect is almost invisible, and the protection afforded by its colouring is at once apparent. In the autumn evenings it is often very abundant at the blossoms of the white rata.
SELIDOSEMA ARISTARCHA, Meyr.
(Selidosema aristarcha, Meyr., Trans. N. Z. Inst. xxiv. 216.)
(Plate [IX]., fig. 17 ♂, 18 ♀; Plate [III]., fig. 17, larva.)
Of this fine species only about a dozen specimens have hitherto been captured, all of which have occurred in the immediate vicinity of Wellington. It is consequently at present a rarity, but future collectors will probably find the insect in many other parts of the country.