On a species of Phasmatidæ destructive to Eucalipti

By William Macleay, F.L.S.

Macleay, W.J. (1881) On a species of Phasmatidæ destructive to Eucalipti. Proceedings of the Linnaean Society of New South Wales,

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At a meeting of this Society last month, Mr. C. S. Wilkinson, the Government Geologist, exhibited three specimens of a Phasma which he had obtained a week or two previously in the vicinity of the Binda Caves, in the county of Westmoreland. He informed the meeting that he had found these insects in amazing numbers in that locality; that the trees for miles around were completely denuded of leaves, and that the dead and dying insects were lying beneath the trees almost in heaps.

The occurrence of a Phasma in such numbers is a very remarkable fact, and perfectly new as far as my experience goes. I judge also from observations made at the time of Mr. Wilkinson's announcement by the members present that all were equally struck with the unusual character of the occurrence. The Phasmidæ or Phasmatidæ as they are now more properly called, are, as we know, all leaf-eaters, and it is rare in any part of the

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country in the summer season to find a gum tree without a few of these inscets grazing on it. But, though very widely and generally distributed, this is the first instance I believe recorded of one of the family being found in such multitudes as to cause the entire destruction of large areas of forest. Mr. Wilkinson's discovery shows, however, that such cases occur, and the question will naturally arise in many minds: “May not the hitherto unaccountable death of gum trees over large areas in different parts of the country be due to the occasional superabundance of the leaf-eating Orthoptera?” Among the many causes suggested for the dying out of the gum tree over large areas, as may be seen for instance throughout a large portion of the Lake George Basin, I hare heard the opossum named, and this probably, because observers may have noticed the dying trees looking as if their leaves had been enten ; but I never cculd believe that an animal which, like the opossum, is fond of travelling long distances at night in search of food would fix himself to leafless trecs for a period long enough to cause their death. But Mr. Wilkinson's Phasma clearly dees denude trees completely cf their leaves, and it is inevitable that a tree submitted to such a process for two or more consecutive years must die.

From what is known of the habits of the Phasmatidæ, I should say that they are the most likely of all insects to retain their position on a tree or in a mass of trees as long as they possibly can, and that whea their food supply is exhausted by the death of the tree, they drop to the ground and die. Many of the Phasmatidæ, no doubt, have wings, and Mr. Wilkinson's species rather large ones; but, unlike their saltatorial and migratorial brethren, the Gryllidæ and Locustidæ, they seldom use them, and never take long flights. Among the Phasmatidæ most, if not all, the adult insects die at the beginning of winter, dropping off the trees as soon as the frosts set in, but they have previously fastened their egg-cases securely on the upper branches, so that the warmth of spring produces an abundant crop of young to complete the destruction commenced by their parents.

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Mr. Wilkinson has kindly presented me with the specimens he exhibited at last meeting. I find them to be of a new and undescribed species, closely allied to the well-known Sydney species Podocanthus Typhon, but differing in some important particulars. I name it after its discoverer.

PODOCANTHUS WILKINSONI.

Head above, behind the antennæ, with several impressed longitudinal lines, antennæ twenty-four jointed, about the length of the anterior legs in the male, shorter in the female. Prothorax narrower than the head, and becoming narrower to its junction with the mesothorax, its length being about equal to the length of the head behind the antennæ; the mesothorax is rather narrower and scarcely longer than the prothorax except at its base, where it widens out; it is covered beneath and on the sides with small tubercles, and on the back with a double row of five larger tubercles; the metathorax is longer than the mesothorax, and much wider ; it is sharply tuberculated beneath, as are also, thouglh in a less degree, the abdominal segments. The tegmina are rather pointcd - in the female half the length of the wings, in the male about one-third. The wings are moderately large and equal in both sexes. The legs are rather short; the hind femora strongly dentated beneath on the inner and outer edge, with a deep groove between; the intermediate femora are armed in the same way, but not so strongly; and the anterior are grooved beneath, but not dentated. The basal joint of the tarsi is a little the longest, except in the intermediate legs.

The specimens have been in spirits and therefore it is impossible to make out the colouration with certainty, but the body seems to have been of a reddish-brown, almost black beneath, the wing coverts yellowish, with the median carina brown, the costal area of the wings brownish-yellow, and the wings themselves hyaline, without any visible rosy tint. Length of male three inches six lines; the female is not longer nor bulkier than the male. This

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uniformity of size in the sexes, if constant, is, I believe, quite unprecedented in this family of insects.

If it should be found that the ravages of this or any other species of the Phas matidæ are the causes of the wide-spread destruction of trees now going on in many parts of the colony, it will, I think, be a simple matter to limit, where the timber is of sufficient value, the extent of the injury by clearing a wide belt round infested spaces.