Family Psychidæ.
Œceticus omnivorus (Plate [X]., fig. 1 ♂, 1a ♀, 1b larva, 1c ♂ pupa).
This insect is very rarely seen abroad, but can be easily reared from the larva, which feeds on manuka and other plants throughout the year. When very young, and in fact immediately after leaving the egg, it constructs a wide spindle-shaped case, principally composed of silk, with a few small fragments of leaves, &c., attached to the outside. It has a large aperture in front, through which the head and anterior portion of the larva are projected, and a much smaller one at the posterior extremity, which allows the pellets of excrement to fall out of the case as they are evacuated. The body of the enclosed caterpillar is of a light straw colour, the head and three first segments being dark brown, with numerous white markings. The abdominal segments are considerably thickened near the middle of the insect, rudimentary prolegs being present on the third, fourth, fifth, and sixth segments of the abdomen. The anal prolegs are very strong, and are furnished with numerous sharp hooklets, which retain the larva very firmly in its case. As it grows it increases the length of its domicile from the anterior, causing it gradually to assume a more tubular form, tapering towards the posterior aperture, which is enlarged from time to time. The outside is covered with numerous fragmentary leaves and twigs of various sizes, placed longitudinally on the case, and frequently near the anterior aperture, the materials, owing to their recent selection, are fresh and green. The interior is lined with soft, smooth silk of a light brown colour, the thickness of the whole fabric being about the same as that of an ordinary kid glove, and so strong that it is impossible to tear it, or indeed to cut it, except with sharp instruments. The size of the case when the caterpillar is mature varies considerably, ranging from 25 to 30 lines or more in length, and about three in diameter, the widest portion being a little behind the anterior aperture (see Fig. 1b).
During the day the larva closes the entrance and spins a loop of very strong silk over a twig, the ends being joined to the upper edges of the case on each side; in this way it hangs suspended, the caterpillar lying snugly within. I have often known a larva to remain thus for over three weeks without moving, and afterwards resume feeding as before; this probably occurs while the inmate is engaged in changing its skin. At night the larvæ may be seen busily engaged: they project the head and first four segments of the body beyond the case, and walk about with considerable rapidity, often lowering themselves by means of silken threads; the only locomotive organs are, of course, their strong thoracic legs, which appear to easily fulfil their double function of moving both larva and case. If disturbed, these insects at once retreat into their cases closing the anterior aperture with a silken cord which is kept in readiness for the purpose, and pulled from the inside by the retreating larva. This operation is most rapidly performed, as the upper edges of the case are flexible, and thus fold closely together, completely obstructing the entrance. When full fed, this caterpillar fastens its case to a branch with a loop of strong silk, which is drawn very tight, preventing the case from swinging when the plant is moved by the wind, and also rendering the insect's habitation more inconspicuous, by causing it to resemble a broken twig. The anterior aperture is completely closed, the loose edges being drawn together and fastened like a bag. The posterior end of the case is twisted up for some little distance above the extremity, thus completely closing the opening there situated. It is lined inside with a layer of very soft silk, spun loosely over the sides, and partly filling up each end. In the centre of this the pupa lies with its head towards the lower portion of the case, the old larval skin being thrust backwards amongst the loose silk above the chrysalis. In this stage of existence the extraordinary sexual disparities, which are so characteristic of the family, manifest themselves, the male and female pupæ being very widely different in all respects. The former is figured at 1c, the female pupa differing from it in the following particulars. It is much larger and more cylindrical in shape, the abdomen occupying nearly the whole of the body, and consisting of nine visible segments, the terminal one being obtusely conical. The head and thorax are very rudimentary, more resembling those of the larva than the male, all the appendages being, however, reduced to hardly visible warts. In colour it is pitchy black and shining, and its length is about ten lines. This insect remains in the pupa state during the winter months, viz., from May till September. When about to emerge, the male chrysalis works its way down to the lower end of the case, forces open the old aperture there, and projects the head, thorax, and upper portion of the abdomen, the pupa being secured from falling by the spines on its posterior segments, which retain a firm hold in the silk. Its anterior portion then ruptures, and the moth makes its escape, clinging to the outside of its old habitation, and drying its wings. It is probable that the female insect does not leave her case, communication with the male being no doubt effected through one of the orifices, and the eggs afterwards deposited inside. On one occasion I found a case full of eggs, containing the shrivelled body of the female and her old pupa shell, which would seem to confirm the above opinion. The perfect insects are drawn at Figs. 1 and 1a. The male (1) is extremely active, dashing about the breeding cage with great rapidity when first emerged, and rapidly beating his wings to tatters; but the female (1a) closely resembles a large maggot, all the appendages being completely rudimentary, except the two-jointed ovipositor at the end of her body; she is incapable of any motion, except a slight twirling of the abdomen, which takes place while the eggs are being laid.[[17]]
Family Noctuidæ.
Leucania nullifera (Plate [XIII]., fig. 3, 3a larva).
This large, though dull-looking insect, is occasionally taken at light during the summer and autumn months.
The larva feeds on the spear-grass (Aciphylla squarrosa), an abundant plant on the coast hills near Wellington. It devours the soft central-growing point, and its presence in a tussock can be at once seen by a quantity of pale-brown "frass," visible at the bases of the leaves. The formidable spear-like points with which this plant is armed must afford the caterpillar considerable protection from enemies. As a rule a single specimen only is found in each clump of the grass, so that the female probably deposits her eggs singly. This larva is full-grown about August, and may be found feeding in the plants during the autumn and winter.
The pupa state is spent, in an earthen chamber, amongst the roots of the spear-grass, and the moth emerges during the summer.
This species occurs at considerable elevations. I have seen it as high as 4,000 feet in the Nelson province, where its food-plant may also be found.