Part 76

"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, 1b 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 , 17 ; 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.

The perfect insect appears in October and November. Although it must be common, it is rarely seen; specimens are consequently best obtained in the pupa state and reared in captivity. The easiest way to find the pupa is to pass a straw into the horizontal burrow, and move it about until it touches the trap-door. The collector is at once apprised of this circumstance by a distinct hollow sound, produced by the straw when it comes in contact with the lid, which acts like a miniature drum. If no such sound is heard after moving the straw into every possible position, it may be assumed either that the insect has left the burrow, or that it is inhabited by a larva only. When, however, a pupa is actually discovered, a section of the tree-trunk should be cut out, extending from about two inches above the horizontal burrow to about one foot below it, and the log, thus obtained, taken home. Should a number of pupæ be found in one tree the whole trunk may then be taken, if practicable, and kept in a well-lighted room or a conservatory, until the enclosed insects emerge. The specimens usually come out of the pupa at about five or six o'clock in the evening, and if intended for the cabinet should be killed before dark, as they very soon injure themselves when flying.