Stick or Leaf Insects

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Notes on stick or leaf insects, with an account of Podacanthus wilkinsoni, as a forest pest, and the spiny leaf insect, Extatosoma tiaratum, in the orchard.

From AGRICULTURAL GAZETTE OF N. S. WALES. 16: 515-520
June, 1905.
Miscellaneous Publication, No. 862.

WALTER W. FROGGATT, F.L.S.,
Government Entomologist.

THE large size and grotesque form of the orthopterous insects belonging to the Family Phasmidæ, better known under the popular name of Stick or Leaf insects, has always brought them under the observation of entomological collectors, and though very little is known about the early stages of the development of our commonest species, many of our larger ones were described at a very early date, chiefly by G. R. Grey, Westwood, and Macleay. Isolated descriptions of single specimens are apt to be misleading, as the difference in the sexes in some species is so marked that it has led to them being frequently described as distinct forms. In some groups both sexes are wingless, in others while the females are wingless the males are furnished with large flying wings, and are much smaller and slender in form.

They are amongst the most helpless of insects, and from their large size are destroyed by many birds, but, in compensation for their helplessness, nature has endowed them with most remarkable powers of imitative mimicry to the foliage among which they live and feed. Not only do their colours harmonise, but their wings, legs, and head are often covered with leaf-like spots and markings, the margins scalloped and crenulated in imitation of their food plants, so that in spite of its large size, if the insect remains motionless, it will easily escape detection right under one's eyes. They have a general appearance to the carnivorous Mantis, which, however, puts on its mimic livery to more easily capture its prey, but they can be distinguished at a glance by the difference in the structure of the fore legs which are used for walking, and are without claws or spines. They lay their eggs singly, dropping them on to the ground below, while crawling among the foliage. The eggs are rounded, enclosed in a very hard shell, and many of them are wonderfully like seeds. They often remain for upwards of two years on the ground before the larva makes its way out, a helpless stick-like creature, with slender body and legs, and though no parasitic enemy could get at them in the egg state, such helpless creatures as these baby phasmids must have an immense number of enemies in the first few weeks of their childhood. Australia is rich in large and remarkable looking species of phasmidæ, about fifty-four having been described, while probably in the interior many others

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are still to be discovered, for although the casual entomologist often finds them from their awkward bulk they become damaged or destroyed in transit, and are difficult things to keep in perfect condition when collected.

The Ringbarker (Podacanthus wilkinsoni, Macl.).

This stick insect was described by Macleay in the Proceedings of the Linnean Society of New South Wales in 1889, from specimens obtained by the late Government Geologist, Mr. C. S. Wilkinson, near Binda Caves, who stated that they were so numerous at that date that large tracts of forest trees were completely stripped of their foliage, and appeared to be dying from their attacks. Macleay in commenting upon these notes said that it was probable that in many cases where the trees were found to be dying out, from no apparent cause, that it might frequently be brought about by the infestation of this or other allied species of plant-eating phasmids.

Bushes denuded of foliage by Podacanthus wilkinsoni.

In 1891, Oliff, in the pages of this Gazette, published a note on this insect; they were recorded as very numerous at Murphy's Creek, near Walcha, and since then they have been recorded as appearing in similar swarms every alternate year, which points to the fact that it takes two years from the time the eggs are dropped on the ground until the perfect development of the phasma.

Through the kindness of Mr. J. F. Campbell, the District Surveyor at Walcha, with whom I have been in communication for a few years on this interesting subject, I was enabled this season, 1905, to visit the district infested by this gregarious stick insect, collect specimens, and make notes on the damage caused by their presence.

The country over which they range is about 50 miles long, comprising a wide strip of forest, including what is known as Murphy's Scrub, through Upper Tia, and Noundoc Station to the Gulf, a depression in the mountains towards the Manning River, in which district they are known as the “Ringbarkers,” “Murphy's Ringbarkers,” or “Lowrie's Flying Gang,” on account of the dying brown appearance of the trees covering the ranges after they have been feeding through them. So like the effects of ring-barking upon the trees is this damage, that I was told that many years ago the forester, new to

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the district, noting the brown foliage, accused the squatter of ring-barking timber on leasehold land without permission. At the present time (February), the adult insects are hanging in couples, or clambering over the tops of the young gum scrub, which are completely stripped of every leaf right down to the ground in many instances, while the tops of the large gum trees above are quite leafless, and many of them covered with dead branches that have died back for several feet from the effects of former attacks.

All species of eucalypts are devoured, but no other scrub trees are molested.

The young insects emerge from the eggs upon the ground in the early summer, but are not noticeable until they take on a yellow and black banded tint; growing rapidly, the bulk of them are full-grown about New Year, and commence laying their eggs towards the middle of February, and continue into March, when those that survive die with the first frosts which may come early in April in this district. Therefore, the eggs now being laid will remain dormant until the early summer of 1906, and the next crop of phasmids will be at New Year, 1907.

The adult male measures 3½ inches from the front of the head to the tip of the abdomen, with the slender antennæ in front about an inch longer, and across the expanded wings 4 inches. The general colour is dull green with brownish tints on the legs, the tegmina or forewings leaf-like, and edged with white on the outer edge, the hind wings with the front stripe opaque green, the base orange red, all the semitransparent portion pink with a shade of purple.

The head is rounded, the mesothorax forming a rounded neck covered on the upper surface with a number of conical spines; the legs and abdomen long and slender, the latter furnished with a clasping apparatus above the genitalia, and slender cerci at the extreme tip of the abdomen.

In several immature males collected at the same time, the mesothorax is fully twice the length of the adult, without any dorsal spines; the tegmina and wings small and rounded at the tips; the thighs of the hind leg stout and cylindrical, with two large black spines in the centre of the under surface not present in the perfect insect, and the male genitalia and claspers are undeveloped, simply represented by a swelling at the apex of the abdomen.

The female is of a very similar structure in the head, legs, and thorax, but of a lighter green tint, though it is very variable. The tegmina is light green, with the front margin of the hind wings of a similar tint, except the basal portion, which is a rich reddish orange tint, the membranous portion a deep purplish pink, somewhat brighter than that in the male wings. The abdomen is swollen, but tapering to the tip, is of the same green tint as the tegmina, with pinkish markings between the wings; the under surface of the abdomen roughened and almost black. On account of her thickened abdomen she looks shorter than the slender male, but the measurements both in length and across the wings are about the same. There is a variety often noticed among the females which have the whole of the tegmina, front of the wings, and abdomen reddish salmon colour.

The eggs are over one-sixth of an inch long, rounded behind, truncate at the summit, with a round plug projecting from the centre like the stopper of

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a bottle. They are black in colour, with delicate fringes of plush-like material forming wavy lines all over the outer surface. Their numbers can be estimated by the fact that on one hillside in an area of about ¼ of an acre I collected about 500 specimens of these insects, which simply covered the low scrub; when handled the females eject a drop of fluid from the mouth, which has a sickly offensive smell, which may have some protective influence in regard to their enemies among the birds, for though the birds were plentiful, I did not notice any species feeding upon them, though I was informed by residents that the magpies, crows, and laughing jackasses do somtimes eat them. I was told too that in the ring-barking season, when the fowls eat them, the yolks of the eggs get a curious colour and are considered uneatable, just as in the western plains in the locust season, the fowls that eat them lay discoloured eggs.

Extatosoma tiaratum.

One squatter, whose young pigs died from the indigestion caused by the chitinous wings and legs, had the run of a paddock where the insects were plentiful on some low gum scrub where they could reach them.

The forest country, tenanted by this phasmid army at present, contains little timber of special value, but though they have been confined to this strip of country for so many years without spreading to other districts, altered conditions might cause them at any time to spread.

The clearing of tracts of country in their haunts has now broken up the once united swarm into several minor armies, and when once they can rise from the ground they can fly very well, and their wings (before the females become distended with eggs) are capable of carrying them considerable distances with a favourable wind. In good forest country they would cause immense damage, for the trees, denuded of their foliage, shoot out from the butts, often forming quite a thick scrub, and the wood does not split freely where it is being constantly damaged. In such a way the phasmid could develop into one of the worst forest pests in Australia, and be one very difficult to deal with.

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In conclusion, my thanks are due to Mr. S. Watts, of Upper Tia Station, and Mr. Albert Lowrie for their kindness in showing me over the infested country, and furnishing information as to the phasmid's range and habits.

The Spiny Leaf Insect (Extatosoma tiaratum, Macleay, W. S.)

This species was originally described by W. S. Macleay in the appendix of King's Survey, published in 1827, under the name of Phasma tiaratum, but as the insects collected during King's voyages came from all parts of the Australian coast, there was no exact locality given. In 1833 G. R. Grey, published “The Entomology of Australia, Part I; Monograph of the Genus Phasmidæ,” illustrated with fine coloured plates of all the then known species; in it he figured and described both sexes of this insect, calling the male “Hope's dilated-bodied Spectre,” a rather cumbersome name (Extatosoma hopei), though he seems to have thought it might be the male of Macleay's

Extatosoma tiaratum on Japanese Holly, showing imitative mimicry.

species from the similar form of the head and legs. It is furnished with well-developed wings, their front margin green, and the network blackish, interrupted with whitish bands circling round, and its body is long and slender. In describing our species, which he called “Macleay's dilated-bodied Spectre,” Grey says that his specimen was armed at the tip of the abdomen with a strong sharp curved black claw, which must have been some malformation, as the genitalia is very pronounced in this species. In conclusion, Grey says that “Mr. Cunningham has kindly informed me that they live on the saplings in the neighbourhood of Parramatta.”

The female measures up to 5 inches in length from the front of the head to the tip of the abdomen; general colour dark green with the upper surface clouded with a smutty tint, like that upon the foliage caused by black fumagine, while the sides of the segments are mottled with

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white and brown imitating the shades of the moss and lichens found on the tree-trunks. The head is small, with a curious crown on summit, the thorax and abdomen swollen out into a rounded body edged with spiny flaps, the elytra represented by small bracts, wings wanting, and the legs dilated and scalloped like holly leaves. Three specimens were captured by an orchardist, Mr. Flusburgs, of Brunswick River, who found them in the foliage of his peach trees, into which they had probably wandered out of the surrounding scrub. When unpacked they were placed on a pot plant in the office window, where they hung in all manner of curious attitudes, sometimes holding on with only a single claw, at other times with two, but a favourite attitude was with the head thrown back and holding on with all the feet. They would remain motionless like this, except when carefully changing their position. On the journey down they laid a number of eggs, and here they continued egg-laying, a single egg falling at intervals on to the paper beneath the jar. The eggs are about the size of a large radish seed, somewhat oval in form, flattened on the sides, light brown in colour, with a creamy, glazed mark round one side, and a cork-like plug on the summit. They lived in this manner for eight days, then their legs began to relax, and they kept falling to the ground and died, evidently before their time, because when opened large numbers of eggs were found in their ovaries. Examination of a number of specimens shows that each phasmid lays about 100 eggs. This phasma has a very wide range, being recorded from Tasmania, the east coast of Victoria, along the tropical scrubs of New South Wales, Queensland, and New Guinea. In nearly all cases where I have collected this insect I have only come across single females, and never seen the male in its native state. The capture by Mr. Flusburg of three specimens of this phasmid is a unique experience.

[One Plate.]

Stick Insects
1. Podacanthus wilkinsoni (male), 2. Podacanthus wilkinsoni (female), 3. Podacanthus wilkinsoni (immature male), 4. Podacanthus wilkinsoni (hind leg, immature male), 5. Podacanthus wilkinsoni (egg).

Sydney: William Applegate Gullick, Government Printer. - 1905.