The Magpie Moth

Dominion, Volume 28, Issue 104, 26 January 1935, Page 20

The Magpie Moth

(By

J. Drummond.

F.L.S., F.Z.S.. for “The Dominion.”)

THE magpie moth is very much in evidence this summer. Its sooty black wings, picked out with white, and the golden girdles on its body, make it conspicuous in fields, gardens and wild places. Unlike most moths, it feels that the light is sweet, and it loves the sunshine. It does not rush through the air helter-skelter, but Hies leisurely, as if wishing to bask in the warmth. There is no record of the number of eggs a female magpie moth lays, but brood after brood reared every season is sufficient to account for this insect's position as one of the commonest moths in New Zealand. Its great profusion influenced Dr. D. Miller, Chief Entomologist at the Cawthron Institute, when writing "Garden Bests in New Zealand,” to sketch its life history as typical of an insect that goes through a complete metamorphosis. An insect’s life history covers its career from the embryo in the egg to the adult form. There are species that do not alter much from infancy to the adult form except in size. These go through no metamorphosis. The silverfish, a slender night prowler covered with glittering scales that come on to ihe lingers like silky powder, is in this class. A newly hatched silver-fish is identical in form with a grown-up silver-fish. Earwigs, crickets, cockroaches and other insects go through a partial metamorphosis. Moths and butterflies are amongst insects that have a complete metamorphosis before they become adults; and complete metamorphosis is one of the world’s wonders, a complex process that involves in I he life history of a single individual stages almost inconceivably different one from another. Dr. Miller's sketch of the magpie moth’s life history begins when a female lays eggs on the under-surface of-a leaf. The eggs are pale green at first, but soon become yellowish, and then leaden. When- nearing the time

to be hatched, an embryo nitty be seen through the transparent egg-shell curled inside. The youngster bites a hole through its egg, and crawls out, a caterpillar one-sixteenth of an inch long. Its first impulse is to eat. Finding itself on a food-plant, it eats continually night and day. It moults several times until it is a fully-grown caterpillar, known as a woolly bear, an inch and a half long, black and hairy, with red lines on its sides. Before its final moult, it stops eating and wanders in search of a suitable place in which to go through its first metamorphosis. The site selected usually is amongst stones or rubbish, or under loose bark. There it spins a cocoon of white silk, entangling the long black hairs on its body in the silken strands.

In the cocoon, it falls into deep inertia. It cannot walk, cannot eat, has no desire to do either. Changes creep over it and through it. Instead of v an active caterpillar, devourer of plants, it has become a chrysalis, threequarters of an inch long, black or brown marked with yellow, Ou the horny covering there ean be traced the legs, wings, feelers, head, chest ami abdomen of the moth that will arise from the chrysalis. After about two weeks, perhaps three, four or live weeks, a cross-shaped slit is made on the back of the chrysalis behind the head. A perfect adult magpie moth draws out. At first, it is almost helpless. The body soon hardens, and the moth realises that it has wings to fly with, wings that are no longer soft and crumpled. Complete metamorphosis has taken place—tirst the egg. then the eaterpillar, I hen the chrysalis, then the perfect moth.

Outwardly, the caterpillar and the adult moth are as different as any two things ean be. One is wormlikb. wingless and voracious; the other is comely, vies with birds in grace of flight, daintily sips nectar from flowers, and is so elegant that it never eats at all.