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Life Stories from Nature
New Zealand's Great Ghost Moth, Hepialus Virescens

(Written for the “New Zealand Railways Magazine” by H. Collett.)

The Ghost Moths (Hepialidae) of worldwide distribution, form a rather interesting study. They are without any known allies, and wanting in both frenulum and proboscis. Purely nocturnal in habit, little is known of their “life stories,” yet, to judge by the fecundity of the females, the family must have a host of enemies, especially during the larval period. The matured insects do not appear fitted out to take nourishment, theirs seems to be a case of “stored energy,” on the depletion of which the moth, no longer possessing strength for flight, falls and becomes an easy and living prey to ants. “Charagia” is frequently found in the Australian bush, fallen to the ground, or lying in the forks of trees, covered with small ants, literally devouring him alive, without sufficient power either to fly or shake his vivisectors off.

There are 150 varieties of Hepialidae known, of which twelve are indigenous to New Zealand. They vary greatly in colouration and size.

“Hepialus Virescens,” of New Zealand, is a truly regal insect, both as regards size and colouration; the female is the larger, with a wing spread of five inches as against four inches in the male. Apart from size, the sexes are easily distinguishable, even though the colouration is somewhat similar–a bright green on the forewings with the hindwings a brownish red at the base, that merges into pale green towards the outer edge. The female has conspicuous black markings on the forewings, green thorax marked with two black bands across. The first six abdominal segments are brown, the last three green. The male has less conspicuous markings on the forewings, but carries a row of seven white spots on each, about a quarter to half an inch from the edge. The thorax is green and bears a black cross, whilst all the nine abdominal segments are brown.

The larvae are of a light yellow, bearing a spot on each segment, the twelfth of which is brown, with the head of much darker shade. There are many food plants, but the one most favoured is the wild New Zealand currant (aristotelia racemosa). The pupa also is yellowish laterally, shading into dark brown at the head.

The larvae bore galleries in the main stem of the food plant, of an intricate and unique design that is worth describing. It has an opening to the air curtained off in silk, woven and coloured so as to completely resemble the surrounding bark, and on an exact level with it. These tunnels traverse the trunk, about three inches from the surface, in a downward direction.

When the pupal stage approaches, a far more intricate tunnel is made, which ends in a spacious cavity just below the bark, and with a large air vent exquisitely camouflaged in silk so as to exactly resemble the three scars. Three other large tunnels converge into this, the central one running into the heart of the trunk; the other two, to the right and left, just underneath the bark. The central tunnel has an upward tendency for a short distance, so as to give immunity against flooding; then, it travels horizontally to the centre of the tree and ends abruptly.

Again this is an instance of perfect camouflage; if the gallery floor is carefully examined a trap door will be discovered near the end. This trap door is circular and of hard silk, so constructed as to appear exactly like the tunnel walls in colour and texture. If this lid, which is slightly larger than the bore, is raised–a difficult thing from the outside–a vertical tunnel fourteen to eighteen inches deep, will be disclosed bearing downwards. At the very bottom of this the pupa will be found in an upright position with the terminal segment of the case supported on the discarded larval skin. The object of this lid is undoubtedly to keep out predatory intrusion to the chrysalid dormitory.

As the chrysalid approaches maturity it takes on darker tones of colour, the dark marking of the coming moth becoming apparent through the case months prior to its emergence. Instances are known where the pupa remains colourless almost, and the green wings of the imago appear suddenly through the case weeks before the final metamorphosis.

When the final change is imminent the pupa works upwards, lifts the lid, which responds to the slightest pressure inwardly, and gains access to the air, emerging all but the last three segments, which remain in the tunnel. Presently the thoracic shield bursts, the perfect moth wriggles free, rests upon the tree till the wings are sufficiently hardened for flight—then it flashes off into the unknown to its mating and destiny!

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