Leaf and Stick Insects: Order Phasmatodea

Phasmids are insects that eat leaves and resemble leaves or sticks.

They are usually green or brown but may reveal brightly coloured underwings when they fly. They have developed many unusual shapes to camouflage themselves to avoid detection by predators. The order Phasmatodea includes the longest insects in the world.

Habitat and Distribution

About 150 species of phasmids are found in Australia. They usually live in gum trees but are sometimes found in gardens on rose bushes or fruit trees. However because of their excellent camouflage, they are often overlooked. When disturbed, a phasmid may sway, imitating a dead leaf or stick swaying in the breeze. During summer many people have found stick and leaf insects in the laundry, clinging to windows, and drowned in swimming pools. The attractive green and pink Podacanthus typhon is one species that is often found.

Most species of phasmids are quite rare but a few such as Podacanthus wilkinsoni can occasionally occur in plague numbers, causing extensive damage to eucalypt forests. In the 1960s, a series of devastating outbreaks occurred in mountain forests of Victoria, New South Wales and the Australian Capital Territory. Other species that can reach high densities include Didymuria violescens, and Ctenomorphodes tessulatus.

Appearance

Marked variations in body features and colours occur in many species of phasmid. Horns, spines and lobes on the abdomen or the legs, may be more or less developed, or completely absent, in the same population. Some species have green and non-green forms. Many of these features may also vary geographically, together with overall size, relative wing length, and the colour of the hind wings, if present.

The longest Australian phasmid is the Titan Stick Insect (Acrophylla titan) which can grow to 25 cm long.

Reproduction

Many female phasmids do not need to mate in order to produce fertile eggs. This form of reproduction is called parthenogenesis and all the eggs produced will hatch into females. If the females do mate with a male before producing eggs, the nymphs (babies) may be male or female.

Spiny Leaf Insects

One interesting Australian phasmid is the Spiny Leaf Insect (Extatosoma tiaratum), also called Macleay's Spectre Stick Insect. The females of this species have very large bodies but very short wings and are unable to fly. The males are long and slim with fully developed wings. Spiny Leaf Insects are popular pets in Australia and also overseas.

Female Spiny Leaf Insects are not only larger than the males, but also live longer, surviving for up to 18 months. They lay thousands of eggs during their adult life, flicking them onto the ground below their perch. The eggs have a knob, called a capitulum, which is attractive to ants. Ants carry the eggs back to their underground nests, eat only the knob, and leave the rest of the egg in the nest, protected from other animals that might eat it. The young phasmids (or nymphs) hatch after one to three years underground and look and behave like red-headed black ants. They emerge from the ant nest and climb rapidly upwards, looking for soft green leaves. In a tree, they moult into a green or brown, slow-moving leaf mimic. The females live for about 18 months, while the males are only short-lived, surviving for around 6-8 months.

Back from the Brink - the Lord Howe Island Phasmid

The Lord Howe Island Phasmid or Land Lobster (Dryococelus australis) may be the rarest insect in the world, and possibly also the rarest invertebrate. It was originally found only on the remote Lord Howe Island (700km NE of Sydney), but was thought to have been extinct for the last 80 years, after decimation by rats introduced after a shipwreck in 1918. However, in February 2001 three living specimens were found by a team from New South Wales National Parks and Wildlife Service (NPWS), the Australian Museum and the Lord Howe Island Board on the remote pinnacle of Ball's Pyramid (16km south of the island). The NPWS is now preparing Interim Recovery Actions to protect the species, along with a Species Recovery Plan. It is hoped that the large flightless insect (15cm long) may one day be reintroduced to its former range.

References

• Clyne, D. 1978. How to Keep Insects as Pets. Angus & Robertson: Australia.
• Horne, P.A. and D.J. Crawford. 1996. Backyard Insects. Melbourne University Press.
• Hughes, L. 1996. When an insect is more like a plant. Nature Australia 25(4 ): 30-38.
• Wilson, S. K. 1990. Throwing your babies at the enemy. Geo: 12(4): 106-113.
• Rentz, D.C.F. 1996 Order Phasmatodea: Leaf and Stick Insects. Pp 244-257 in Grasshopper Country. UNSW Press: Sydney.