New Zealand Moths and Butterflies/Psychina
V.—THE PYRALIDINA.
Not dealt with in this volume.
VI.—THE PSYCHINA.
The Psychina are distinguished by the following characters:—
"This ancient group, which furnishes the origin of the five preceding, is not now very prominent, though much more numerous in warm regions.
"Imago with fore-wings more or less elongate-triangular, hind-wings ovate, often rather small.
"Larva with 10 prolegs, usually with few hairs.
"Pupa with segments 8-11 free, usually 7 also (except in Psychidæ), in male 12 also; protruded from cocoon in emergence."—(Meyrick.)
The Psychina and Micropterygina are included amongst the Micros by most modern authors. I have, however, described and figured certain conspicuous and interesting species belonging to both these groups. The insects in question have, until so very recently, been regarded as Macros, that I think it would be a mistake to omit them in the present volume. There can, however, be no question that the modern view is the correct one, and that notwithstanding the large size of some of the species, they are really closely allied to those Micro-Lepidoptera, with which they are now associated.
Of the Psychina we have one family represented in New Zealand—the Psychidæ.
Family 1.—PSYCHIDÆ.
"A rather small family of universal distribution, but commoner in warm countries. Male imago with thinly scaled wings, without markings; flight strong and swift, sometimes in sunshine. The female is almost wholly helpless; the abdomen is at first greatly distended with eggs, and ultimately shrivels up.
"Ovum oval, smooth. Larva inhabiting a strong portable silken case, covered with fragments of stick or refuse. Pupa within the larval case."—(Meyrick.)
There are two genera in New Zealand closely allied to each other.
1. Œceticus.2. Orophora.
Genus 1.—ŒCETICUS, Guild.
"This generic name was wrongly spelt Oiketicus by its originator and others, for which there is no possible justification. I have corrected it."—(Meyrick.)
Although I have made several examinations of fully denuded wings of Œ. omnivorus, I have been unable to discover any trace of the additional veins mentioned by Mr. Meyrick. The hair-like scales which clothe the wings of this insect are very long and slender, and might easily be mistaken for a short vein, if placed in the requisite position. I am disposed to think that the examination of undenuded specimens has led to the discrepancy between the results.
We have one species.
ŒCETICUS OMNIVORUS, Fereday.
(Liothula omnivora, Fereday, Trans. N. Z. Inst. x., 260, pl. ix. Œceticus omnivorus, Meyr., Trans. N. Z. Inst. xxii. 212.)
This interesting species is seldom seen as an imago in the natural state, although the cases constructed by its larva are of common occurrence. Specimens of these cases have been noticed at several localities between Palmerston, in the North Island, and Invercargill, in the South Island, so that apparently the insect is common, and generally distributed throughout New Zealand.
The eggs of this species are deposited inside the old case, which the female insect never leaves during the whole of her life. The young larva when first hatched is about ⅛ inch in length. Its head and three anterior segments are corneous and much larger than the others, which are rather soft with the exception of the last one. These little larvæ are extremely active, and immediately after hatching leave the old case, and roam in all directions over the tree, letting themselves down from branch to branch by silken threads. They carry the posterior portion of their body elevated in the air, walking whilst doing so by means of their strong thoracic legs.
The food-plants of this species are numerous. The following are a few of them: Manuka (Leptospermum scoparium and ericoides, Cupressus macrocarpa, Pinus insignis), and various species of willow, &c. These, it will be observed, include several introduced trees. In fact, the insect is a very general feeder. About three days after leaving the egg, the little caterpillar constructs a minute, conical-shaped, silken case, which it carries almost in an upright position on its posterior segments. Later on in life this case becomes too heavy to be held vertically, and is afterwards dragged along by the larva, and often allowed to hang downwards. The case has two apertures—a large one in front, through which the head of the larva is projected, and a smaller one at the posterior extremity, which allows the pellets of excrement to fall out of the case, as soon as they are evacuated.
Owing to the apterous and completely helpless condition of the female imago, it is evident that the dispersal of this insect must take place in the larval state. Distribution is of course quite impossible without a female being transported in some way, and from observations made on a good many larvæ of various ages, I am disposed to think that the migration of this insect to new localities takes place at an early age, possibly soon after its emergence from the egg. On this account I think that the occurrence of the moth in both North and South Islands is of great interest, as it would seem to indicate the existence of some connection between the two islands, at a period not sufficiently remote to have allowed any appreciable modification to take place in the insect's structure and habits. At the same time, it should be borne in mind, that the protection afforded the larva by its case, and its ability to feed on so many different plants, may have rendered any modification unnecessary for the preservation of the species during recent times. The length of the full-grown caterpillar is about 1 inch. The head is dull yellow speckled with black. The first three segments are very hard, dark brown, with numerous white markings. The remaining segments are considerably thickened near the middle of the insect, rudimentary prolegs being present on the seventh, eighth, ninth, and tenth segments of the larva. The anal prolegs are very strong, and are furnished with numerous sharp hooklets, which retain the larva very firmly in its case. As the caterpillar 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 2¼ to 3 inches or more in length, and about ¼ inch in diameter, the widest portion being a little behind the anterior aperture.
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 whilst 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 grown, 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 insect.
The male and female pupæ may very easily be distinguished. The male pupa is rather attenuated, and has all the organs of the future moth plainly indicated on the integument, as is usual with lepidopterous pupæ. The female pupa, on the contrary, is merely a chain of segments, with a few faint indications of rudimentary organs on the anterior extremity. It is, moreover, much larger than the male pupa.
The insect remains in this condition during the winter months. About September the male pupa works its way down to the lower end of the case, forces open the old aperture there situated, and projects the head and thorax, 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 breaks open, and the moth makes its escape, clinging to the outside of its old habitation, and drying its wings.
The perfect insect must be about from September till December, but I have never then observed it. The only specimen I have seen was noticed flying very rapidly in the street in Wellington, in July. I was at first unable to tell what species it was, as it had a most unusual appearance on the wing, but its subsequent near approach enabled me to ascertain for certain that it was a specimen of this insect. In captivity I have also noticed the extreme activity of the male when first emerged. Indeed this moth is so vivacious, that it often happens, owing to the emergence usually taking place very early in the morning, that specimens are more or less injured by their efforts to escape, before they are discovered in the breeding cage. This restless energy of the male is no doubt essential to the insect's well-being, as the females, hidden away in their cases and incapable of any movement, must of necessity be very hard to discover. The power of locomotion lost in the one sex is thus doubled in the other. Considering the protection afforded this insect by the case, which it inhabits during its preparatory stages, its enormous mortality from the attacks of a parasitic dipteron (Eurigaster marginatus) is very remarkable. In this connection the following analysis of 38 cases, gathered at random, may be of interest:—
26 had parasites.
8 were dead.
2 contained eggs.
2 contained living pupæ, 1 male and 1 female respectively.
Amongst some of these parasites I once obtained a specimen, which was in its turn infested by a secondary or hyper-parasite, belonging to the genus Pteromalus, in the order Hymenoptera. Eighteen of these minute insects emerged from a single pupa of E. marginatus. The method by which the Pteromalus introduces its eggs into the dipterous larva, which is in its turn enclosed in a caterpillar, is not at present known to entomologists; but it seems probable that the eggs of the hyper-parasite are either deposited in the eggs of the dipterous insect, or else on the very young larvæ, before they penetrate the skin of the caterpillar.[1]
Genus 2.—OROPHORA, Fereday.
We have one species.
OROPHORA UNICOLOR, Butl.
(Plate XIII., fig. 7 ♂.)
This odd-looking little insect has been found by Mr. Fereday, at Rakaia.
The life-history is thus described by Mr. Fereday: "I have never seen the larva. Its case measures in length about 16 lines (1⅜ inches); the exterior is covered with pieces of stems of grass from a line to 5 lines in length, laid longitudinally and in the manner of thatch; the interior is thinly lined with fine silk. The cases are found fixed to the twigs of the Wild Irishman (Discaria toumatou), but it may be inferred from the covering of the case, that it probably does not feed on the shrub but upon the tussock grass, generally growing where the shrub is found. It is some years since I found the cases on Discaria toumatou, growing in the river-beds of the Rakaia and Waimakariri, on the Canterbury Plains, and I did not find any case in its earlier stage before the larva had fed up and changed into the pupa state."[2]
All Mr. Fereday's specimens were bred from the cases, and to the best of my belief no one has ever observed the insect on the wing. It is evidently a very scarce species, and is probably restricted to a few river-beds in the South Island.