The green instars of caterpillars of O. eucalypti have substantial coloured warts with spiky hairs, see http://lepidoptera.butterflyhouse.com.au/satu/eucalypti.html This is not O. eucalypti. It does not look like any of the 997 caterpillars illustrated on the Coffs Harbour Butterfly website: file://localhost/C:/Users/donhe/Dropbox/Webpages/larvae/cats.html I do not know what it is. It would be good to rear it in captivity to the adult moth, which we could more easily identify.