IN TOUCH WITH NATURE

Otago Daily Times, Issue 20866, 5 November 1929, Page 2

IN TOUCH WITH NATURE

THE STICK INSECTS. By J. DRUMMOND, fx.s., f.z.s. Although introduced birds take many stick insects in New Zealand, these strange creatures are still fairly plentiful in almost all parts of the Dominion, except towns and cities. They are not seen often because their effective methods of mimicking twigs in their plant homes give them a large measure of concealment. Nature has created many famous mimickers in the flies, the beetles, the moths, the butterflies, and other orders. Stick insects, probably, are the most famous of them all. Drop a stick insect on the ground, and only sharp eyes will disclose its presence. Usually, a stick insect resembles a dry twig. It then is a dirty grey or a brown. In other cases, it is so green that its coat makes a perfect match with the foliage amongst which it clings inertly. Stick insects no not beautiful. They represent the ugliness of insect life, if they are judged merely on appearances. In other respects—life cycle from egg to perfect insecthood, development, structure, rhythm of organs, and so on, —they are as beautiful as any either insects; and in insects is not only skin deep. There is a stick insect in New Zealand so uncomely that an entomologist christened it, in Greek, the horrid thorny-skinned stick insect. The female, which is much larger than the male, reaches a length of six inches. The spines on its body may or may not be an additional protection, as they are formidable to some extent. The dull brown colour certainly is protective More so are pale patches that resemble lichens. Few individuals of this stick insect are - in collections. Entomologists sometimes take it at night. _ Looking for other insects, they discover it feeding on the leaves of shrubs. The flash of a light induces it to become absolutely motionless at once. Its fancy favours the lovely white rata as a food plant.

A female stick insect takes no care of her eggs or her young,’ In this she is a contrast to the earwig and to many beetles. She lays her eggs singly on the ground, at random. Mass production may be a good thing in human industry. With some insects and fishes it allows for heavy losses by enemy attacks. On the oJJier hand, stick insects’ eggs, lying singly on the ground, are not ao conspicuous as they would be in masses. Each egg is enclosed in a tiny horny chest. There may be a further protective ruse in this contrivance, as an egg may be jnistaken for the seed of a plant ot the pea family. To add to the resemblance, on one side of the chest there is a mark liko the mark on pea-seeds at the point of attachment to a pod. This resemblance has not been explained. A suggestion is that it is intended to deceive parasitical ichneumon flies; but observations have shown that ichneumons are not deceived. They lay their eggs in the chests, and the young ichneumons feed on the young stick insects. The resemblance may protect the eggs from insectivorous birds, but it increases the risk of attention from aeed-eating birds.

On hatching, a young stick insect pushes up a lid on the chest and bursts into tho higher life. It' has difficulty m getting rid of its old little prison. Hooks on the youngster’s hind legs seem to catch in the skin of the egg. A strange feature of this phase of a stick insect’s life is that when it emerges it is three times as large as the egg. The discrepancy is explained by tho fact that expansion takes place during emergence. Before emergence, the legs are fairly close together. In the struggle to escape from the egg, the hind joints of the middle body lengthen and spread out. The young one grows rapidly and casts its skin several times before it becomes a grown-up.

In moulting there sometimes ig difficulty m getting a limb free from the old skin. The limb may snap off. One stick insect, it is believed, sometimes “*tes the limb of another stick insect. If these losses are suffered in the early '.-art of a stick insect's life, the defect 13 temedied by/replacement of the lost limb, on the same plan as crabs and lobsters follow. At the next moult a new limb appears on a reduced scale. The following moult will disclose a limb less out of proportion to the other limbs. If a hmb is lost late in life, there are not sufficient moults to allow completion of the process. In any case, stick insects cio not exert themselves much! sluggishness is their characteristic; the loss of a limb is not a great disaster. A stick insect’s toot ends in two sharp hooks. Between these there is a little cushion. By this contrivance, a stick insect can grasp a twig quickly, and it cap retain its hold securely, in spite of branches being shaken in the wind.

All New Zealand's stick insects—l 4 species have been listed-—are wingless. When wings are present in stick insects in other countries the male’s are larger and better than the female’s. There are species in which only the males have wings. Males are comparatively rare, f eey are slenderer than the females, and often are less spiny. Brown and green are the fashionable colours. They vary greatly with growth, and, it is believed, with the seasons. The young of one species, at least, on leaving the egg on the ground, and climbing up the stem of a j 8 ° ro ' vn - It becomes green when it feeds amongst the leaves. It revdrts to brown 'again if it finds that it is necessary to mimic a fairly thick twig. Some have green marks on brown, resembling minute liverworts, that cover stems and leaves. Many stick insects unpleasantly eject an acid liquid with a bad smell. This practice has not been noted amongst New Zealand’s stick insects. In other countries there is a belief that if the liquid gets into a person’s eye it will cause blindness.

Mr 6. \. Hudson, of Wellington, observed a New Zealand species of stick insect for several months. In the spring months, he saw many litjde stick insects on parasitical ferns that cover the stems p.itrees in forests. “ They are curious little creatures,” he states. “ Their antics when they mimic inanimate twigs are very amusing.” Stick insects’ hind legs, unlike the hind legs of their relatives, tue grasshoppers, are useless for leaping. Their forelegs, unlike the forelegs of another, relative, the mantis, are useless tor seizing prey. As they are strict vegetanans, this is no disadvantage. Much of their attenuated stick-like appearance is due to the elongation of their forebodies, to which the legs and wings, if any, are attached.

A young Isew Zealand entomologist who takes the stick insects in hand might give attention to a remarkable feature of stick insect life noted in Europe. Some species there reproduce generation after generation without a single male appearing. Males of these species are very rare. When they are found it is seen that they are much smaller than the females, and much less conspicuous. Many thousands of individuals of an Indian species DixipPus, have been born in captivity in the Old Country, but never a male amongst them. In spite of this, the females continue to lay fertile eggs. An English breeder of these insects supplied all his entomological friends with eggs or young, and still was at a loss to know what to do with the nbundant surplus.

A few weeks ago Mr J. A. M'Leod. Onehunga. asked if anybody except Mr S. Marks and himself had heard a singing mouse. Mrs Louise Calvert states, in reply, that when she lived in Marlborough “ark, Ireland, she heard and saw a singing mouse, which, for several mornings, ran round the floor of her bedroom. It wae caught in a trap and killed. Using a lens, she examined the body: and found a white growth, as large as a big pga, partly covering the entrance to the windpipe. Mrs Calvert believes that if she had not caught the mouse the growth would have covered the larynx, and the song would have been finished.

“ You occasionally give instances of birds nesting in queer places,” a resident in a Christchurch suburb wrote on October 10. " You may be interested to know that _a pair of starlings have built their nest in my letter box, which has a smeffkt large slot, to admit papers. There are five eggs. I am interested to discover if the parents will see the job of hatching atnd rearing the young through. Although there is only a ' baching ’ whare on the place, the box i is opened six days a week from once to [ five times a day. Do not publish my | address, in case a mischievous boy interferes with the starlings.”