Part 21

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 {125}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 {126}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.[66]

Genus 2.--OROPHORA, Fereday.

"Ocelli present. Antennæ 2/3, in male moderately bi-pectinated throughout. Labial palpi rudimentary, hairy. Abdomen densely hairy. Fore-wings with veins 4 and 5 short-stalked, 7 and 8 out of 9. Hind-wings with veins 4 and 5 stalked, parting-vein well defined, 8 connected by bar with cell beyond middle, and additional vein (9) rising out of 8 before bar."

We have one species.

OROPHORA UNICOLOR, Butl.

(_Psyche unicolor_, Butl., Proc. Zool. Soc., London, 1877, 381. _Orophora toumatou_, Fereday, Trans. N. Z. Inst. x. 262, pl. ix. _Orophora unicolor_, Meyr., Trans. N. Z. Inst. xxii. 212.)

(Plate XIII., fig. 7 [M].)

This odd-looking little insect has been found by Mr. Fereday, at Rakaia.

The expansion of the wings is hardly 1 inch. _All the wings are rather broad, rounded, and very sparsely covered with dusky brown hair-like scales_; the body is very hairy, and the antennæ are slightly bi-pectinated. The female is apterous.

The life-history is thus described by Mr. Fereday: "I have never seen the larva. Its case measures in length about 16 lines (1-3/8 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."[67]

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.

{127}VII.--THE TORTRICINA.

Not dealt with in this volume.

VIII.--THE TINEINA.

Not dealt with in this volume.

IX.--THE MICROPTERYGINA.

The following are the principal characters of the _Micropterygina_:--

"Fore-wings with an oblique membranous dorsal process (jugum) near base, forming with the dorsal margin a notch or sinus, which receives the costa of the hind-wings. Hind-wings without frenulum, 1_c_ present, with 11 or more veins, neuration essentially, almost or quite identical with that of fore-wings. Fore-wings and hind-wings more than usually remote at origin.

"In the two families, which constitute this highly interesting group, is fortunately preserved a type of _Lepidoptera_ whose existence could never have been inferred from a study of other forms. Without a knowledge of these two families the true origin of the order could never have been more than a matter of more or less probable conjecture. The _Micropterygidæ_ are the primeval ancestors of all the Lepidoptera, indicating their origin from the _Trichoptera_ so nearly that one or two more discoveries might make it hard to draw any line of demarcation. The _Hepialidæ_ are an offshoot from the _Micropterygidæ_ (with considerable extinction of intermediate forms), constituting a separate line of development quite unconnected with any other _Lepidoptera_; if, as is possible, this separate stem may have ever given rise to other branches forming distinct families, all trace of their existence seems to have been lost.

"Imago with fore-wings and hind-wings more or less semi-oval, termen and dorsum forming a nearly uniform curve.

"Larva with few hairs, with 10 to 16 prolegs, or apodal, living concealed.

"Pupa in _Hepialidæ_ with segments 7 to 11 and in male 12, in _Micropterygidæ_ with all segments free."--(Meyrick.)

In this work the _Hepialidæ_ alone are dealt with, the _Micropterygidæ_ being reserved {128}for a future work. It may, however, again be mentioned that the last-named family contains amongst its New Zealand representatives _Palæomicra chalcophanes_, a species which more closely approximates in structure to a Neuropterous insect than does any other member of the _Lepidoptera_. This insect is consequently regarded by Mr. Meyrick as the most ancient species of the order yet known. The survival of _Palæomicra_ in New Zealand is quite in accord with the existence of such forms as _Apteryx_ and _Dinornis_ amongst the birds, the tuatara lizard (_Sphenodon_) amongst reptiles, and _Peripatus_ amongst _Myriapoda_, archaic forms which have been preserved in this country through its long isolation from continental areas, and the resulting absence of more recent competing forms.

Family 1.--HEPIALIDÆ.

"Head rough. Ocelli absent. Tongue obsolete. Maxillary palpi obsolete. Tibiæ without spurs. Fore-wings with all main veins and costa connected by bars near base, 1_b_ furcate, forked parting vein strong." (Plate I., figs. 22, 23, 24, 28, 29.)

"By no means an extensive family, yet of universal distribution. It stands more conspicuously isolated than any other group of _Lepidoptera_, for although it is without doubt a terminal development from the _Micropterygidæ_ (that is one from which no existing family has originated), the gap between them is considerable; exotic genera, whilst differing in various details, are remarkably uniform in the more important peculiarities of structure, and do not at all tend to bridge the gap. The relatively large size of the _Hepialidæ_ (of which some species exceed six inches in expanse of wing) may be attributed to the larval habits, which render these insects independent of the seasons or fluctuations of food-supply, thus removing the check which ordinarily limits growth. The modified type of neuration may have resulted directly from the increase of size, involving a great strengthening of the main veins beneath the costa to support the weight. As a consequence of this strengthening, the flight of the larger species is very powerful, and to this, combined with a choice of larval food, which is often rather indiscriminate, may perhaps be ascribed the wide range of the group, rather than to its antiquity. It is probably of Indo-Malayan origin, and must have existed in that region long enough to acquire fixity of type before its dispersal, which, geologically speaking, may not have been exceedingly remote."--(Meyrick.)

There are two genera represented in New Zealand.

1. HEPIALUS. 2. PORINA.

Genus 1.--HEPIALUS, F.

"Antennæ 1/8 to ¼, in male lamellate or simple. Palpi short, drooping, hairy. Posterior tibiæ usually densely rough-haired, in male sometimes with long projecting tuft above. Fore-wings with vein 7 from angle, 8 remote, 9 and 10 stalked. Hind-wings as fore-wings, 8 seldom connate or stalked with 7." (Plate I., figs. 22 and 23, neuration of _Hepialus virescens_, 24 head of ditto.)

"A genus of universal distribution, but not very numerous in species. Ovum spheroidal, smooth. Larva elongate, active. Pupa with segmental whorls of spines, enabling it to move actively before emergence."--(Meyrick.)

Represented by one species only--the largest moth we have in New Zealand.

{129}HEPIALUS VIRESCENS, Dbld.

(_Hepialus virescens_, Dbld., Dieff. New Zeal., ii. 284; White, Taylor New Zeal., pl. i. 6. _Hepialus rubroviridans_, White, l.c., pl. i. 1. _Charagia virescens_, Walk., Bomb., 1569; Scott, Trans. Ent. Soc. N. S. Wales, ii. 28. _C. fischeri_, Feld., pl. lxxx. 1. _C. hectori_, Butl., Proc. Zool. Soc. Lond., 1877, 380. _Hepialus virescens_, Meyr., Trans. N. Z. Inst., xxii., 211.)

(Plate XIII., fig. 16 [M], 17 [F]; Plate III., fig. 23 larva, 30 pupa.)

This large and conspicuous insect appears to be generally distributed throughout the North Island.

The expansion of the wings of the male is 4 inches, of the female sometimes fully 5½ inches. The fore-wings of the male are _bright green, with a series of paler ring-shaped markings between the veins; an irregular row of white spots crosses the wing near the middle_, and a small white spot is situated on the costa at the base. The hind-wings are very pale yellowish-brown near the body, becoming pure white in the middle, and pale green on the termen. The head and thorax are green, the abdomen is white, tinged with green at the apex. The female has all the wings of a relatively more attenuated shape; _the fore-wings are green, mottled with black_; the hind-wings are pale reddish-brown, shaded with green near the termen; the abdomen is also reddish-brown, becoming green at the extremity.

The species is rather variable in both sexes. In the male the white spots on the fore-wings vary considerably in size, and there are occasionally several additional spots near the body. In the female the black markings of the fore-wings are sometimes much more extensive than the green ground colour. This dark form of the female was described by Butler as a distinct species, under the name of _Charagia hectori_. In both sexes the green colouring is occasionally entirely absent, a dull orange-brown taking its place. I formerly attributed this peculiarity to the effects of fading, but Mr. Norris has shown me a very perfect specimen of this variety, which he bred from the pupa, he having noticed the orange-brown colouring immediately after the insect emerged.

The transformations of this insect are very interesting. The female lays an enormous number of very small, round, yellowish eggs, which she seems to deposit quite indiscriminately. The young larvæ consequently have to find their way along the ground to the stems of their food-plant, a large percentage no doubt perishing before they succeed in doing so, and this circumstance probably accounts for the great number of eggs produced.

The food-plants of this species are numerous; the following are a few of them: "wineberry" or "currant" (_Aristotelia racemosa_), apparently the favourite; "manuka" (_Leptospermum ericoides_); "ki-ki" (_Astelia solandri_); "black maire" (_Olea apetela_); titoki (_Alectryon excelsum_); and _Melicope_. The larva tunnels the stems of these trees, feeding entirely on the wood, which it bites off with its strong mandibles.

For the most part it inhabits the main stem of the tree, its gallery always having an outlet, which is covered with a curtain of silk and refuse, and is spun exactly level with the surrounding bark, and very inconspicuous. These burrows usually run towards the ground, and are mostly two or three inches from the surface of the trunk. In some instances the larvæ inhabit branches, in which case, if they are small, the tunnels are made near the centre. Later on in its life, but probably some time before its transformation into the pupa, the caterpillar of this insect constructs a far more complicated burrow than the above. It consists of a spacious, irregular, but shallow cavity, just under the bark, having a very large opening to the air, which is entirely covered {130}with a thin silken curtain, almost exactly the same shape and size as the numerous marks occurring at intervals on the trunks of many of the trees. Three large tunnels open into this shallow cavity: one in the centre, which runs into the middle of the stem, and one on each side, which run right and left just under the bark. These lateral tunnels are usually very short, but sometimes they extend half-way round the tree, and occasionally even join one another on the opposite side. The central tunnel has a slightly upward direction for a short distance inwards, which effectually prevents it from becoming flooded in wet weather; afterwards it pursues an almost horizontal course until it reaches the centre of the tree, when it appears to suddenly terminate. This, however, is not the case, for, if the gallery floor be carefully examined a short distance before its apparent termination, a round trap-door will be found, compactly constructed of very hard, smooth silk, and corresponding with the surrounding portion of the tunnel so exactly that it almost escapes detection. When this lid is lifted a long, perpendicular shaft is disclosed, which runs down the middle of the tree to a depth of 14 or 16 inches, and is about ½ inch in diameter. The upper end of this shaft is lined with silk, which forms a framework on which the trap-door rests when closed. The lid itself is of a larger size than the orifice which it covers, and this makes it extremely difficult, if not impossible, to force it open from the exterior, especially as it always fits down very closely as long as the insect remains in its burrow. The object of this contrivance is, no doubt, to prevent the ingress of enemies, large numbers of spiders, slugs, wood-lice, and various orthoptera being frequently found in both central and lateral tunnels, but they are quite unable to pass the trap-door. The galleries of individual larvæ are all wonderfully alike, the only differences observable being in the length of the perpendicular shaft, and in the direction of the horizontal burrow, which is sometimes curved. These variations are usually caused by the presence of other tunnels in the tree, which the larva appears to carefully avoid; at least I have never known an instance where a larva has allowed its tunnel to communicate with another one, whether inhabited or otherwise.

The caterpillar, when full grown, measures from 2½ to 3 inches in length. It is tolerably uniform in thickness, and of a dull yellow colour. The head is large, dark brown, very irregularly striated, and covered with a few short bristles. The first segment is hard and shining with the back and sides ruddy-brown. Its spiracle, which is very large, is situated near the posterior margin, and a little above it there is a dull black spot, filling a slight concavity about the same size as the spiracle itself. Each remaining segment has on its dorsal surface two horny plates, and two similar plates are situated on each side immediately below the spiracle. The body of the larva is thinly covered with yellow and black bristles. In many specimens the ventral surface and connecting membrane between the horny plates is pale purple. Younger specimens differ in being of an olive-green colour, which is much more pronounced, when they are small.

The last act performed by the caterpillar, prior to undergoing its transformation, is the construction of the above-described trap-door at the top of its burrow. This done the insect retreats to the bottom, its posterior segment resting on the termination of the vertical gallery. In the course of a few days the skin is cast off and worked downwards to the bottom of the burrow, underneath the last segment of the pupa.

This pupa varies from 2 to 2½ inches in length. It is attenuated in form and pale reddish-yellow in colour. The head and dorsal portion of the thorax are dark brown and harder than the rest of the body. The edges of the abdominal segments are furnished dorsally with a row of small {131}hooklets above and below all the divisions; on the ventral surface there is only a single row, which is situated in front of each articulation.

As development progresses in the pupa it becomes darker in colour, especially on the wing-cases, where, in some female specimens, the future black markings of the moth are quite discernible as long as two months before emergence. Other specimens remain pale in colour until within a fortnight or three weeks of the appearance of the imago, when the green colouring of the wings suddenly becomes visible through their semi-transparent envelopes.

When about to emerge the pupa works its way up the vertical tunnel by means of the above-mentioned hooklets, forces open the trap-door, and wriggles along the horizontal burrow until it reaches the air, only the last three or four segments remaining in the tree. Its anterior portions then break open and the moth crawls out and expands its wings in the ordinary way, resting on the trunk of the tree, until they are of sufficient strength and hardness for flight.