This species is very common, and generally distributed throughout both the North and the South Islands; it also occurs plentifully at Stewart Island.
The expansion of the wings is 1⅜ inches. The fore-wings are pale plum-colour; there is an indistinct, curved, brownish transverse line near the base; a straight dark brown line across the middle, and a curved series of blackish dots beyond the middle; the apex is pointed, and the termen has a strong projection a little above the middle. The hind-wings are ochreous, with a series of minute brownish dots across the middle.
This is a variable species. The fore-wings are often much clouded with rich brown, and in some specimens scarcely a trace of the original purplish colour remains; the central straight transverse line is often absent, and the other lines are frequently very indistinct, except on the costa; the dots on the hind-wings are also often absent, and occasionally specimens are met with in which all the wings are almost white.
The larva is rather elongate, dull yellowish-brown or greenish-brown; there is a very broad dark brown dorsal line, and several wavy lateral lines; the prolegs are black, the spiracles are also black; there is a slight hump on the posterior edge of each of the last six segments, the hump on the penultimate segment being considerably larger than the others. The length of the caterpillar when full grown is about 1 inch.
It feeds on Pteris incisa, a beautiful pale green fern, attaining a height of four feet or more, and growing in open situations in the forest. This fern is especially abundant on old decaying logs situated amongst light brushwood. When disturbed these larvæ immediately drop to the ground and coil themselves up. In this situation they are very inconspicuous, as their colouring so closely resembles that of the faded fronds or stems of the fern.
The pupa is buried in the earth about two inches below the surface, the insect remaining in this state during the winter months.
The moth first appears about September, and continues in great abundance until the end of March or beginning of April. It frequents forest, and is noticed most commonly in the neighbourhood of its food-plant. There are probably several broods in the course of a year.
SESTRA FLEXATA, Walk.
(Cidaria flexata, Walk. 1421.)
(Plate [IX]., fig. 37.)