NATURE

by VIC JAKES

From time to time over the years I have seen a laughing kookaburra flying away from the tops of the massive eucalyptus trees growing some 50m from the house carrying in its substantial beak what looked, initially, to be a short stick with a cleft at one end. The bird’s excitement, sometimes coupled with the fact another kookaburra was flying in eager pursuit, suggested to me that whatever was being carried was probably some sort of substantial meal. 

A quick check through the binoculars revealed the ‘stick’ was a little floppy and quite bright green in colour, leading me to conclude the precious prize was, in fact, a goliath stick insect (Eurycnema goliath). 

Endemic to Australia, it is the second largest stick insect to be found here after the titan stick insect. It is, however, not widespread, with its strongholds being here in south-east Queensland and north-eastern New South Wales, with small populations in northern Queensland, mainly around Cairns, and a few sightings in the Northern Territory.

These massive insects – the males can grow to 15cm and the females 20cm – are folivorous (leaf eaters) and favour eucalyptus and broad-leaved acacia trees. It is reported a fully grown insect will eat about 10 leaves each day. Although officially classed as common, they are, for essential survival purposes, not easy to see and because, from my experience, they seem to prefer the giddy heights near the top of their eucalyptus home. 

I did once see one of these fascinating insects, probably a female, flutter from the upper branches. Quite clearly, so did an ever-watchful kookaburra for, just after it touched the ground, it was quickly pounced upon and the perceived delicacy was immediately whisked away for consumption far from the eyes of any other birds that might be tempted to participate in the banquet.

Both sexes have wings but the females, due to their size and weight, are incapable of real flight, while the males have rather larger wings, which, coupled with less body weight, enable them to fly quite strongly. The insect I was able to photograph does, in view of what can be seen, give rise to quite a number of questions. Bear in mind that this particular male specimen was fully grown around the expected 15cm. While it can be seen that the wing furthest away is perfectly formed, the nearest wing is quite clearly malformed. Was it born like this, or has it been damaged as the insect grew, either by an attacking bird or possibly by being injured while escaping a bushfire? As the insect can thrive simply by crawling about its chosen food-source tree, it is possible that it has lived satisfactorily with this handicap since birth and, all being well, may still be doing so today, if it has not revealed itself to the local kookaburra community.

Before reaching adulthood, our goliath would have gone through five developmental stages called instars, where the exoskeleton is shed to permit growth. At each of these instars, one or more changes will occur in respect of size, colouration, sexual dimorphism (visible differences between male and female), leg length and wing development. The final moult will reveal their apple green colouration and unfolding of wings to their full size. 

To live to the ripe old age of a possible five years, the insect will need to learn all the defensive tricks, including remaining motionless to rely on natural camouflage, flashing the bright red underside of their wings as a warning, kicking its spiny legs and emitting an off-putting hissing sound to deter would-be predators.

Enjoy any sighting you can get of one of these fascinating Sunshine Coast residents.