AFTER WINTER

Auckland Star, Volume LXIX, Issue 208, 3 September 1938, Page 7 (Supplement)

AFTER WINTER

By E. G. Turbott

The Ghost Moth Grows Up

The custom among ghost moths of becoming fall grown in September was broken this year, for one came out in the middle of Aug-ust. It was c-aught promptly by a cat, perhaps because the cold made it too drowsy to look out properly for enemies. The early stages of this big moth's life are spent deep in a growing tree, where the young one eat® the wood in which ;t is liviEg. For over three years, perhaps for five, it is a caterpillar. spending its time burrowing in the wood of the tree. The female, which is larger than the male, as can be .seen in the picture below, lays small yellow eggs. The number of eggs laid is about two thousand, and it is just as well that there are so many, for she does not place theni on the proper food-tree as is done by most moths and butter- • flies. They are laid almost anywhere so that, when the young larvae hatch, they are not able to start eating immediately, but have to meet the j difficult problem of reaching a tree j suitable for their operations. Wine- 1 berry, putaputaweta or lacebark will do, and so will puriri. mangeao. manuka, maire. titoki. naaio. karaahi. beech, broadleaf and even willow, silver beech, oak, poplar or apple, but there may not be trees of this kind in the neighbourhood. Some of the young caterpillars reach the right tree safely, but a large number die. The successful ones dig into the tree immediately with their strong jaws and settle down in the wood. There is enough edible matter in the wood to make it food for the caterpillar, but the caterpillar which is to eat such obstinate stuff must have well-built mandibles. If a ghost caterpillar is examined. the*e jaws, dark brown and scissors-like, are one of its most striking features. As the caterpillar tunnels on into the stem of the tree, generally towards the ground, it does not leave an open front door through which enemies can get in. Over the entrance it weaves a tough curtain of silk mixed with debris, which is exactly the colour of the bark and so level with it as to be almost invisible. It is very difficult to find this entrance to the caterpillar's bore at all: generally his presence is first brought to light when the tree is cut. As described, the caterpillar is found in its burrow for three years or more. One was cut out of a stem in the middle of this winter —it was about three inches long and yellowish with a large brown head and showing a purplish tinge where the skin was thinner. Along the back were small hard plates, one to each segment, but on the whole the larva was soft and without much protection when out of jts wooden stronghold.

When its larval period of eating and is almost over, the caterpillar comes to the surface of the tree and makes a final burrow, much more complicated than the other. On the outside of the tree it makes a groove through or under the bark, and in doing so sometimes ringbarks the tree or one of its branches. This outer groove is covered by a web like that over the entrance, and opening into it is the burrow itself. It is shaped like a 7. first going slightly

upwards towards the tree's centre and then straight downwards for about six inches. The remarkable thing about this burrow, which is used by the caterpillar when it turns into a pupa or chrysalis, is the trapdoor at the top of the upright shaft. In "The Butterflies and Moths of New Zealand"' Mr.

G. V. Hudson says that the horizontal sallerv leading from the entrance cowards the centre of the tree appears to come to an end suddenly. e continues: "This, however, is not e case, for, if the gallery floor oe carefullv examined neat its apparent ter mination. a round lid will be lo - compactly constructed oi very nar , smooth silk, and corresponding wjtft the surrounding portion of the iunne so exactlv that' it almost escapes detection.'" The upper end oi the perpendicular shaft is lined witn % which forms a framework on »mca the lid rests when closed. The lid itself is of a larger size than tne hoie which it covers, and is more or less fastened to the siiken frame-* one, which makes it very difficult, il not impossible, to force it ot>en iroin the exterior, especially as ;t always fits down very closely as long as the insect remains in its burrow. -ir. Hudson says that the object of t:>!=trapQ'vr is. no doubt, to keep out enemies such as spiders. slugs, woodlice and other insects which are Oiten found in the outer tunnel. The young moth spends _ about three month? ?.e a rup'a at tric Dottom of this burrow. Then early in September it wriggles up to the trapdoor. Forcing it open, it passes into the outer tunnel and so reacr.es tne entrance. Fr<"*m this position the adult wriggles its way out oi the chrvsalis skin and pushes through the outer door curtain to reach the open. The female moth is the biggest flving insect in New Zealand. She differs from her mate in beinjj coloured brown on the bind w:ngs and central abdomen, while these areas are dull white in the male. On the rest of the body both are pale green, although the spots on the tore w-n?s are black in the female and white in the maleThe flight of the adults in the darkness is swift and. since they seem unable to resist bright lamps, they are often taught after coming in to the light through an open window They are large, ghostly creatures, eating nothing and are only really known from these sudden appearances from the darkness without. Since the adult insects are rarely seen, an account by Mr. Hudson of rearing the moth is particularly useful and is given in full:—'"The easiest way to find the pupa is to pass a straw or thin flexible stick into the horizontal burrow, and move it about j until it touches the lid. The collector !

is at once apprised of this circunsetance 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 suea sound is heard after moving the straw into every possible position, jt may be assumed either that the insect has left the. burrow or that it i» inhabited by a larva. When, - ever, a T'Upa is actually discovered, a section of the tree trunk should be cut out. extending from about two inches alcove the horizontal burrow to about one foot below it. and the V>2. thus obtained, taken home. Should i. number of papae be found in one tre<the whole trunk aaj then be takfr |if practicable, and kept in a we;! [lighted room or 2 conservatory. u*:t: [the enclosed ir-ert~ emerge. T;.--peciißens usually out of I pupa at about five or six o'clock the evening. . . . '•'The best time o? the to obtain the pupa of this i.n-ect is during September and the first fortn'giit in October, as most of the specimen; are then in that condition. If sections are cut out oi the tree t---o lon2 before the moths emerge, the contained insect may tan to come out. owing to shrinkage of the so*«i C'n this account it is advisable to keep the logs damp. Apart from the indi- • r.tions arrove described, burrows containing larvae may often be known by the fresh pellets which are present near the 07-ening. The vacated burrows frequently have the remains of the old pupa sjk-1] at tne entrance, and generally look snarled and weather-worn. These indications are useful guides to the collector before exploring the burrow with a straw in the manner above described. 7 '