Dominion Museum Notes

Dominion, Volume 31, Issue 106, 29 January 1938, Page 8

Dominion Museum Notes

animated sticks Protective Mimicry Has Taught These Insects To Resemble Twigs Sometimes, wandering in garden or wood, one will notice with surprise what at first glance appears to be an animated twig—an insect so closely resembling an actual piece of vegetation that a second glance is necessary to convince one that it is really a living thing, a marvellous example of protective mimicry, a stick insect, or “walking stick.” These curious creatures are found in many parts of the world, and although often large and grotesque are in reality most harmless and interesting. In many parts of the tropics are found allied varieties which, developed upon parallel lines, have acquired a most remarkable resemblance to green leaves.

Stick insects belong to a family known as I’hasmidae which in turn belongs to the great order of insects known as- the Orthoptera. The Ovthoptera includes, besides Phasmids, the mantids, grasshoppers, wetas, and cockroaches, all of which are familiar insects. The term phasmid comes from a Greek word meaning a ghost, and has been applied to these insects on account of their somewhat spectral appearance. Phasmid Characteristics

Stick insects are curiously modified creatures with characteristic long thin bodies and long thin legs. Some have wings, but many are wingless. The majority resemble sticks, twigs, or grass stems, and when at rest or feigning death, as they often do when disturbed, they are exceedingly difficult, probably the most difficult of all insects, to detect. Some are covered with spine-like outgrowths all over their bodies giving them a resemblance to old lichen-covered bark. Generally there is a marked difference in appearance between males and females. This protective resemblance is generally more highly developed in the females. Thev- are usually larger, sluggish in habits, and wingless. The males are

generally much smaller than the female, active, and winged. Their wings are delicate and membraneous.' folding up like a fan, and when at rest lie along the body of the insect, covered by Ihe hardened wingcases.

All species of phasmids are vegetable feeders, and are exceedingly voracious. They are us a rule, however, never in sufficient abundance to cause any great injury to plants of economic importance. A New Zealand Variety

Although by no means the bulkiestof insects, stick insects are among the

longest insects in the world. Species up to a foot in length are known. In New Zealand the largest 'species is known as Argosarchus horridus. Specimens have been found measuring up to Bin. in length. In Australia, the female of Palophus titan, is winged and measures up to lOin. across the outspread wings. The commonest stick in New Zealand is a slender, bright green coloured form, the female of which measures up to 4in. in length; it is known to science as Acanthoderus prasinus.

The visitor to the Dominion Museum will find specimens of these insects ondisplay. In the show cases there, he may also be attracted and interested by "a peculiar leaf-like looking insect known as J’hyllium crucifolium, or more popularly as “the leaf insect.’’ This is the commonest of a group of Insects known as leaf insects, found only in the moister parts of the Orient, and on the islands of the Indian Ocean. In life these insects are bright green in colour and resemble very closely indeed a leaf or a sprig of leaves. They are closely related to the stick insects. Stick insects on the whole do not lay as many eggs as the average insect. Their eggs are laid singly, and dropped on to the ground or among vegetation. No attempt is made by the female 1o place her eggs in any definite position. Each egg is enclosed in a tough capsule, and resembles more or less a plant seed. The period of incubation of stick Insects' eggs is in' many cases very long. In some species, the eggs may lie on the ground for two years before hatching. The young stick insect resembles closely "the adult, except in size. It has to find its own food plants, and it grows very slowly. Unlike many insects, stick insects are not seasonal, and may be found at any time of the year in New Zealand.