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Introduction to PHASMATODEA (STICK INSECTS)
Phasmids or Phasmatids are stick and leaf insects that are spectacular creatures,generally they are characterised by being medium to very large, usually strongly elongated, broadened or flattened, and their legs are slender with flanges or spines present. They have compound eyes and those that are winged may possess three ocelli, antennae are short to very long (over 100 segments) the tarsi (feet) are made up of 5 segments.
The male is usually winged with the females brachypterous or apterous, the forewing (tegmen) is usually short and thickened with the hind wing having a fan like appearance with the front margin thickened. The females of most species are unable to fly, they usually glide, with some able to fly very short distances. Sexual dimorphism is present, the males being smaller than the females with the nymphs closely resembling the adults. Metamorphosis is incomplete. The Phasmids inhabit the warmer parts of the world, especially the tropics with approximately 2500 species known worldwide, 150 species are known from Australia, mostly endemic and representing two out of the three families.
They are distributed throughout Australia from North Queensland to Melbourne, Western Australia and are found in the drier parts of the outback. They have even been found in Tasmania. Stick insects have attracted much attention because of their remarkable resemblance to sticks and leaves, and also due to their size, some exceeding 30cm in length, Australia's largest species growing up to a length of over 30cm is Acrophyla titan.
Life History Their life histories are all very similar. From high foliage female Phasmids disperse their eggs simply, usually by dropping them to the ground, although some species flick the eggs with their abdomen as they are laid to scatter them further.
Some species stick the eggs to branches or other foliage. Depending on the species the females can lay between a hundred to one thousand eggs, over one, two or even three seasons. Once they are laid the female has nothing further to do with the eggs. The eggs resemble seeds and are usually strongly sculptured and
often patterned. There are often distinct differences in the eggs of different species and they are sometimes used to identify closely related species using a Scanning Electron Microscope (SEM) to produce high magnification micrographs. On hatching the nymphs appear as smaller versions of the adults,
but without wings, and search for suitable foliage for shelter. During the day Phasmids tend to remain still, but become active at night. The Phasmids are slow moving and clumsy, and do not normally take to the wing to escape.
When disturbed some species drop and lie motionless on the ground, this condition is called catalepsy and may last for a number of hours. Other species may open their wings repeatedly showing bright colours to frighten predators. Contrary to popular belief, Phasmids do not eat other insects they are herbivores, they eat Eucalyptus and Acacia spp. and Megacrania batesii feeds on Pandanus. In England breeders rear specimens on Bramble (Rubus spp.), apparently stick insects will eat almost any plant in the family Rosaceae.
Classification
The three families are Phylliidae, Phasmatidae and Timematidae, with the latter not represented in Australia. The leaf insects belong to the sub-family Phylliinae, and Necrosciinae we have two, possibly three sub-families in Australia, with the best known species being Phyllium siccifoium, all other species areconsidered stick insects and belong to a variety of sub-families, the notable ones being; Eurvcanthinae Dryococelus australis believed to be extinct? (See Note below).
Phasmatinae Acrophylla titan longest Australian species
Ctenomorphodes tessuatus males from unfertilised eggs
Eurycnema goiath Sub-tropical AKA giant green stick insect
Phatycraninae Megacrania batesii feeds on Pandanus
Tropidoderinae Didymuria vioescens pest species
Extatosoma tiaratum large & spiny
Podacanthus wikinsoni pest species
Life cycle
Egg (Diapause) Nymph (Instars 1-5 or more) Adults (Sexual and Parthenogenesis) Reproduction mating is usually prolonged with the sperm transferred by spermatophore. The males are fairly rare and many species reproduce via parthenogenesis (usually only females produced), although it is known that in one species Ctenomorphodes tessuatus; males can be produced from unfertilized eggs. Pest Species in Phasmids are few and hard to find, but there are three species that appear in a 7 year cycle, in plague proportions. These species are responsible for damage to a variety of natural Eucalyptus forests in New South Wales and Victoria, usually in Mountainous areas. They are Podacanthus wikinsoni, Didymuria vioescens and Ctenomorphodes tessuatus, if these forests are defoliated in succession they will usually die.
Note.
Dryococelus australis the Lord Howe Is stick insect was rediscovered in February 2001 by a team of scientists from NPWS of NSW, the Lord Howe Is board, the Australian Museum and Insektus.
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