NATURE NOTES.

New Zealand Herald, Volume LXVI, Issue 20402, 2 November 1929, Page 1 (Supplement)

NATURE NOTES.

THE STICK INSECTS.

BX J. DKXJIUIGKD, r.t.S., F.Z.3.

Although introduced birds take many stick insects in New Zealand, thesis 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 largo mea3ui'o 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 theu is a dirty grey, or a brown. In other cases, it is so green that its coat makes a perfect match with the foliage among which it clings inertly. Slick insects are 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 other insects; and beauty 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 uisect. 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 duil 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 j beetles. She lays her eggs singly on the j 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 tlie other hand, stick insects' eggs lying singly on the ground are not so 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 mistaken for the seed of a plant of the pea family. To add to the resemblance, on one side or the chest there is a mark like 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 youpg ichneumons feed on the young stick insects. The resemblance may protect the eggs from insectivorous birds, but ifc increases the risk of attention from seedeating birds.

On batching, a young stick insect pusiies up a Lici on the chest and bursts into the higher life. It has difficulty in 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 ? life is that when it emerges, it is three times as large as 'die egg. The discrepancy is explained by the 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 oi the middle body lengthen arid spread out. The young one grows rapidly and casts its skin several times before it becomes a grown-up. In moulting there sometimes is difficulty in getting a limb free from the old "skin. The limb may snap off. One stick insect, it is believed, sometimes bites off the limb of another _ stick insect. If these losses are suffered in the early part of .1 stick insect's life, the defect is remedied 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 les:;_ out, ot proportion to the other limbs. II a limb 13 lost late in life, there are not sufficient moults to allow completion of the process, in any case, stick insects do not exert themselves much; sluggishness is their characteristic; the loss of a limb is not a great disaster. A stick insect s foot ends in two sharp hooks. Between these tliere is a little .cushion. By this contrivance a stick insect can grasp a twip quicklv, and it can retain its hold securely, in'spite of branches being shaken in the wind. All New Zealand's stick insects —fourteen species have been listed a.re wingless. When wings are present, m stick insects in otber countries, -the male 3 are larger and better than the female s. There are species in which only tno males have wings. Males are comparatively rare. They are slenderer thau the females, and often are less spiny. Brown and green are the fashionable colours. Thev vary greatly with growth, and, i*. is * believed, with the seasons. The \oung of one species at least, on leaving the e~g on the ground, and climbing up the stem of a shrub, is brown. It becomes ,T reen when it feeds amongst the lea\ es. It reverts to brown again if it finds that it, is necessary to mimic fairly thick Iwi". Some have green marks en 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 ii the liquid gets into a person's eye it will cause blindness. Mr. G. V. Hudson, ot Wellington, observed a New Zealand species of stick insect for several months. In the spring months, he saw many little stick insects on parasitical ferns that cover the stems of trees in forests. " They are curious little creatures," he states. "Their antics when they mimic inanimate twigs are very amusing." Stick insiscts' hind legs, unlike, the hind legs of their relatives, the grasshoppers, are useless for leaping. Their forelegs, unlike the forelegs of another relative, the mantis, ara useless for seizing prey. As they are strict, vegetarians, this is no disadvantage. Much of their attenuated stick-like appearance is duo to the elongation of their fore-bodies, to which the legs and wings, if any, are attached. A young New Zealand entomologist who takes the stick insects in bind 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 ara 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 inala 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 abundant surplus.