NATURE NOTES.

New Zealand Herald, Volume LXVI, Issue 20288, 22 June 1929, Page 1 (Supplement)

NATURE NOTES.

BUTTERFLY'S SCENT BAG. ?

BY J. DRUMMOND, F.L.S., T.Z.3.

Gorgeous in orange-brown wings bordered with black, black veins, and small white spots on the margins of the wings, a largo butterfly sent by Mr E. S. White, Pukemiro, near Huntly, would grace any cabinet of moths and butterflies. It has not the delicate beauty of some of New Zealand's moths, but it ranks among the Dominion's most conspicuous members of the Lepidoptera. Particular interest is attached to this butterfly on account of a horny pocket on the second vein of each hind wing of the male of the species. This is a scent-bag, equipped with hairlike scales, one of the remarkable organs possessed oy moths and butterflies. Many males have it, but no females. It is believed that it is used to attract females by an agreeable fragrance, and that it has arisen from sexual selection.

The butterfly sent by Mr. White, Danaida plexinpus, is not common, but some of New Zealand's scented moths and butterflies are among the most plentiful. Observers who test moth 3 and butterflies for their scent usually find this work interesting and pleasant, but occasionally their experience is the reverse of pleasant. It seems to take some time after a male has emerged from its chrysalis stage, and after its wings are fully formed, for the scent secretion to become sufficiently diffused to give off the perfume. Very fresh butterflies are quite, or almost, odourless; old and ragged individuals sometimes are very fragrant.

A pair of butterflies w'ere seen courting. The female was seated on the upper surface of a horizontal leaf. Her wings were folded tightly together, her fore-wings drawn back as far as they could go. About an inch behind her, on the same leaf, there was a male, his body in line with hers, and facing the same way. His wings were close together, but his fore-wings were drawn far forward, their hinder border approaching the vertical, as hers approached the horizontal. At intervals' he suddenly opened and closed his wings, and constantly, almost incessantly, he slightly shifted his position, in a series of little rapid jerks. The males of this species have a strong, pleasant fragrance, compared to the fragrance of sandalwood and Spanish cedar. The fragrance from tiny glands in the skin. It often oozes out through fine pores or it accumulates in the scent-bag. Some ' males have minute reversible brushes, with delicate hairs, which allow the fragrance to diffuse into the air. The brush may be at the end of the tail and the scent-bags on the wings. In thatcase the butterfly must first sweep his wings. In other cases the brush-bag has slender threads. These break up into fine perfumed dust, which is scattered to the four winds. The outset has been described as an animated powder-puff. The sense of smell, which certainty seems to take a part in butterfly courtship, seems to be seated in the clubbed antennae, or feelers. An odour emitted by a male butterfly may be unpleasant, even nauseous, to human beings, but the pleasantest fragrance possible to a butterfly of the opposite sex.

Mr. White's butterfly, Danaida plexippus, usually lays its eggs on the under surface of a leaf. In about five days the caterpillar hatches. Its first act is to turn round and devour its .egg-shell. The caterpillar's head is jet black and polished. Its body- is pale greenish-white, and it is covered with small black bristles, which spring from still smaller warts. In three or four days a dusky band appears across the middle of each joint in the caterpillar's body. At the end of the fifth or sixth day it spins on the leaf a silken carpet,' and prepares to moult. There are four moults. The fullgrown caterpillar is cylindrical, naked, and white, with many black and yellow stripes.

It spins a little tuft of silk on the under surface of a leaf, twig or other object. After entangling the hooks of .its hind legs in the silk it lets go the hold by its other legs, and hangs down. For about twenty-four hours it hangs in that position. The skin along the back behind the head bursts, the front part of the chrysalis forces itself out. The old skin is slipped and crowded back until there is only a small shrivelled mass around the tail. The chrysalis, soft and supple, as described by Mr. G. V. Hudson, hangs heavily from the shrunken skin. It has neither legs nor arms, but it must perform the perilous task of completely extricating itself from the old skin and holding fast to the silk on the plant. Joints of the abdomen ar6 used instead of legs. The shrunken skin is suddenly grasped between the folds of two of the joints, as with a pair of pincers. The chrysalis disengages the tip of its body, and, for a moment, hangs suspended.

Mr. Hudson has given an account of the subsequent proceedings: —"With a few earnest, vigorous, jerking movements it sticks the horny point of its tail into the silk, and fastens it firmly by a rasp of minute claws on the point of. the tail. As soon as the point is fastened tho chrysalis, by a series of violent jerkmgs and whirlings, begins to dislodge the oio skin. Then it rests, ancf graaually cor. tracts aud hardefis The really active work continues for only a few minutes, and tho insect seldom fails to succeed." At the end of about the tenth day the dark, deep colours of tho future butterfly begin to show through the delicate, transparent skin. Suddenly thab> skin bursts open close to tho head. The newly-born butterfly extricates itself gradually, stretches forth its legs, clambers oil to a convenient object and allows its moist, thickened and contracted wings to hang listlessly until they aro fit for one of tho highest faculties, flight.

Wekas cnco were plentiful on Mr, G. D. Greenwood's estate, Teviotdale, North Canterbury. They went near the homestead and, in their characteristic and engaging way, were fearless, tame ajid sociable. Suddenly, without any apparent reason, they recently disappeared. This sudden and inexplicable disappearance of wekas in large uumbers has occurred in other parts of the Dominion. The strange, flightless, intelligent birds seem to bo seized with an impulse to migrate, although their migratory movements have not been noted. A suggestive feature of this phase of weka liie at Teviotdale is that when the wekas were plentiful rabbits were scarce, but no sooner had tlio wekas disappeared than the rabbits increased. Believing that cause and effect between tho wekas and the rabbits are operating, an effort is being made to have wekas liberated on Teviotdalo to induce the birds to como back and check the rubbits.

Mr. T. McGill reports that tho native snail, Paryphanta Hochstetteri, is very plentiful in the Rai Valley, Marlborough. It is favourite food of wild pigs, and he believes that on this account, it will be como extinct in that part, of the Dominion. He mentions that starlings, blackbirds, and somo other birds do not seem to be put out when their eggs are handled in the nests. If eggs are taken the birds continue to lay. A hoy took an egg from a goldfinch's nest. It was replaced by the female with another egg. A few days later a second egg was taken, but the complement was again made up. On the other hand. Mr. McGill touched an egg in a skylark's nest, at Richmond Brook Station, Marlborough. There were three eggs in tho nest. The following morning all the eggs had disappeared and the nest had been destroyed; He haii the same ex. perience with a skylark's nest at Dunsandel, Canterbury. On the bank of the Mangaheu River he found several wekas nests. There were three eggs in one nest, under a papa cliff. Mr. McQill's nephew handled one of those eggs, and all disappeared. . <