Photo by huntervalley
The scribbly gum is a eucalypt tree which has played host to the scribbly gum moth (Ogmograptis scribula). The moth lays its eggs between the old and new season’s bark and as a result, a wonderful set of ‘scribbles’ are revealed when the tree sheds the old bark.
There is much more information about the Scribbly gum tree to be seen and a good place to start would be the Australian National Botanic Gardens website or the Wikipedia page on scribbly gums.