Order PHASMIDA

Phasmatodea

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Order PHASMIDA

Stick Insects

Compiler and date details

15 June 2009 - Updated by ABRS following Brock & Hasenpusch (2007, 2009).

30 June 1997 - John Balderson, D.C.F. Rentz & A.M.E. Roach, CSIRO Entomology, Canberra, Australian Capital Territory, Australia

Introduction

The Phasmida, commonly known as stick and leaf insects, are large (35–240 mm in length), terrestrial, often thamnophilus or tree-dwelling insects attaining the greatest abundance in tropical climes. In terms of length, they are among the world's largest insects. Most species show remarkable resemblance to plant parts, such as twigs, leaves and stems. Several species have been used widely in behavioural and physiological studies while others have been of considerable use in cytological investigations.

Kevan (1982) estimated that 2500 species of Phasmatodea were described worldwide; Brock and Hasenpusch (2009) give a figure of 'about 3000' species worldwide. Key (1991) estimated that the Australian fauna would probably reach about 150 species when all species are described. Brock & Hasenpusch (2007, 2009) list 104 described species for Australia.

Genetic variation in anatomical characters occurs in many, if not most, species. This has led to many errors in taxonomy. Lobes, 'horns', spines and differences in rugosity can be highly variable or absent among individuals of the same population. Green and non-green morphs also often occur in the same population. This, coupled with geographic variation, size and wing variation, and the fact that males are much smaller and quite different in appearance from females, has confounded the taxonomic literature. Velona et al. (2015) employed bar-coding and "uncovered cryptic diversity" in Australian stick insects: "Eighty-two specimens representing twelve morphospecies (Sipyloidea sp. A, Candovia annulata, Candovia sp. A, Candovia sp. B, Candovia sp. C, Denhama austrocarinata, Xeroderus kirbii, Parapodacanthus hasenpuschorum, Tropidoderus childrenii, Cigarrophasma tessellatum, Acrophylla wuelfingi, Eurycantha calcarata) were correctly recovered as clades through the molecular approach, their sequences forming monophyletic and well-supported clusters."

Stick insects have had a taxonomic history somewhat similar to that of cockroaches and mantids. They were considered as a family of Orthoptera in the early days but are now generally recognised as a separate order. However, the names used for the order often vary with the author. Cheleutoptera, Phasmida, Phasmodea, Phasmatodea, Phasmatoptera and Phasmoptera have all been used to designate the order. The classification used in the Australian Faunal Directory follows the online checklist of Brock (2013) with a minor modification, following the molecular systematic analyses of Bradler et al. (2014).

Bedford (1978) provided a comprehensive, world review of the biology and ecology of stick insects. Kevan (1982) provided a similar review at the taxonomic level. His 'escalated' view of the higher taxonomic levels is not followed here. Regular notes on the behaviour and ecology of stick insects, including Australian species, can be found in the Newsletter of the Phasmid Study Group (ISNN 0268–3806) and their journal, Phasmid Studies (ISSN 0966–0011).

Brock and Hasenpusch (2009) give a very useful comprehensive review of stick and leaf insect biology and history of collecting of Australian stick and leaf insects. They also detail methods for collection, rearing and preserving stick insects and give a summary of information on each of the described species.

Phase differences (often called kentromorphism in Australia) have been reported by Key (1957) in three Australian stick insects. These are Podacanthus wilkinsoni Macleay, Didymuria violescens (Leach) and Ctenomorphodes tessulatus (Gray), all of which can reach high population numbers. Low density nymphs are uniformly coloured—usually green, while those prone to high density populations are aposematically coloured and patterned. Morphometric phase differences are analogous to those of locusts. There is no correlation between density and activity, and stick insects show no obvious gregariousness.

One species, the Lord Howe Island stick insect, Drycocelus australis (Montrouzier), was believed to be extinct (Gurney 1947; Smithers 1969). It was endemic to Lord Howe Island where it lived on the trunks and in cavities of banyans. It is thought to have been exterminated after rats were introduced to the island in the early part of the century. It was found on the offshore Ball's Pyramid in 2001, and is being reared for release back on the Island.

Most stick insect species seem to be nocturnal and, with a few exceptions, rare in nature. Most species are found in foliage upon which they feed but a few are wholly terrestrial. They are entirely plant feeders and are unusual in their ability to develop on a wide variety of unrelated plant species. They exhibit cryptic postures and perform rhythmical swaying when disturbed. A few species can produce sound when disturbed by rubbing the hind wings against tubercles on the legs. There is no indication that they can hear any of the sounds they produce. When disturbed, some species drop to the ground in a state of catelepsy that may last for hours. Other defensive responses in Australian species have been described by Bedford & Chinnick (1966). Australian Megacrania species squirt a milky substance smelling of peppermint, probably actinidine for M. alpheus Westwood (Chow & Lin 1986), at intruders when disturbed.

ANATOMY
Morphologically, stick insects are very distinctive. They are generally prognathous with the head ovoid to rectangular, often with horns or protuberances. The antennae are short to long, ranging from 8 to more than 110 segments. Eyes are small and inconspicuous; ocelli are present only in some winged species. The prothorax is longer than the other thoracic segments (in contrast to the stick katydids, Tettigoniidae: Phasmodinae, in which the metathorax is the expanded thoracic segment). All three pairs of legs are gressorial and are long and slender. Tarsi of all Australian species are 2–5-segmented. Many species have the capability of being able to regenerate lost appendages if they are lost at an early stage of development. In those limbs, the tarsi are 4-segmented. Terminal claws bear an arolium. Both sexes of most Australian Phasmatodea are apterous, however, males of some species are fully winged, the females wingless or semi alate. The forewings are toughened tegmina, which are often small, rounded and dome-like and cover the base of the hind wings at rest and slightly overlap. The forewings typically have a knob-like structure dorsally in the proximal portion that accommodates a prominent sclerite on the base of the hind wing when folded. The hind wings are large, broad, with a large membranous anal area, folded fan-like at rest. Venation is very uniform; costa absent in forewing, weak and positioned on the anterior margin of hind wing; subcosta unbranched; radius unbranched in forewing, branching in hind wing forming R1 and radial sector; media bifurcate in forewing, in hind wing only basally and occasionally trifurcate.

Abdomen cylindrical or dorso-ventrally compressed, with or without spines or outgrowths; abdomen 11-segmented with the first tergite called the median segment, connected to metanotum (Australian species); tenth tergite well developed, emarginate posteriorly in males with ventro-caudal angles produced, clasping, often with small tufts of spines, lateral walls of this tergite curving ventrally or meeting the mid-ventral line anteriorly; eleventh tergite constituting the supra-anal plate, often concealed under T-10 in males, more elongate, often articulated in females. Sternite 10 well developed, fused posteriorly to the paraprocts. Cerci unsegmented, long or short, often concealed beneath the tenth tergite, often modified as claspers in males. In males the ninth sternite constitutes the subgenital plate which lacks styles but is modified distally into a cup-like lobe, often termed the poculum. The tenth sternite in males of some groups is provided with a backwardly projecting prong-like process, the vomer, which is used in copulation. The genitalia are concealed by the subgenital plate and constitute a group of symmetrical, membranous or lightly sclerotised lobes. Females are different in the structure of the posterior abdominal segments. The eighth sternite consists of a scoop-like or keeled structure called the operculum, the posterior margin of which may project beyond the abdomen and frequently bears an egg. The ovipositor is very short and consists of three pairs of valves, and is wholly concealed by the operculum.

The chromosome complements of Australian Phasmatodea range in number from 26 to 69, the larger numbers occurring in parthenogenetic species. Males usually are XO but XY species are known. Intricate studies illustrating chromosome races have been done by Craddock (1972) and varying chromosome numbers in parthenogenetic females have been demonsrated in the genus Sipyloidea by John et al. (1987).

Eggs of stick insects are of special interest because of their resemblance to seeds. The chorion is hard and may be wrinkled or smooth and patterned. The anterior pole bears an operculum and it in turn may bear a median prominence, the capitulum. On the dorsal surface there is usually a well-defined micropylar plate that resembles the scar-like hilum of seeds. The microstructure of stick insect eggs provides many reliable taxonomic characters. The eggs of Sipyloidea nelida Rentz are unique in that they are enclosed in two supernumerary membranes. Shortly after deposition, the membranes rupture and a system of tubules in the operculum everts forming a cluster of stellate hairs resembling the head of a dandelion. These have been shown to be connected to the inside of the egg and may transport moisture.

Stick insect nymphs may or may not resemble adults. They are often mimetic, resembling ants. Males undergo fewer moults than females and the exuviae are usually eaten. The number of antennal segments increases progressively.

Acknowledgements

Originally this section of the Australian Faunal Directory was derived from the Zoological Catalogue of Australia database, from which the published Catalogue (Balderston et al. (1998) was prepared at CSIRO Entomology, Canberra and the Division's resources and facilities were made available to the authors.

The authors were greatly aided by the kindness of several individuals. The Phasmid Study Group is an international organisation of amateurs and professionals dedicated to the understanding of the systematics, biology and ecology of stick-insects. Several members of that organisation provided invaluable help: Mr Paul Brock contributed photographs and notes on the type specimens of a number of Australian species he had studied in the BMNH and various museums in Europe. He also helped to locate important literature which was unknown to the authors prior to the study. Mr Phil Bragg, also a member of the above-mentioned organisation, provided the authors with a copy of his Phasmatid Database. This document will eventually list all of the stick-insect taxa and their dates of publication, references, type localities and location of types. The authors acknowledged the comprehensive catalogue and reference list of Australian species prepared by Vickery (1983) and thanked Mr Jon Prance of the CSIRO Black Mountain Library for assistance and time spent with the literature search.

The illustrations used in the family introductions in the published Catalogue are from Key (1991). They were reproduced with permission from CSIRO Entomology and the Melbourne University Press.

Funding was made available for the original checklisting project by the Australian Biological Resources Study.

Database Notes

The original information on the Australian Faunal Directory site for the Phasmida was derived from the Zoological Catalogue of Australia database compiled on the Platypus software program. It has now been upgraded and updated following Brock and Hasenpusch (2007, 2009).

Limital Area

Distribution data in the Directory is by political and geographic region descriptors (IBRA) and serves as a guide to the distribution of a taxon. For details of a taxon's distribution, the reader should consult the cited references (if any) at genus and species levels.

Australia is defined as including Lord Howe Is., Norfolk Is., Cocos (Keeling) Ils, Christmas Is., Ashmore and Cartier Ils, Macquarie Is., Australian Antarctic Territory, Heard and McDonald Ils, and the waters associated with these land areas of Australian political responsibility. Political areas include the adjacent waters.

Terrestrial geographical terms are based on the drainage systems of continental Australia, while marine terms are self explanatory except as follows: the boundary between the coastal and oceanic zones is the 200 m contour; the Arafura Sea extends from Cape York to 124°E; and the boundary between the Tasman and Coral Seas is considered to be the latitude of Fraser Island, also regarded as the southern terminus of the Great Barrier Reef.

Distribution records, if any, outside of these areas are listed as extralimital. The distribution descriptors for each species are collated to genus level. Users are advised that extralimital distribution for some taxa may not be complete.