Stuart Rae

Scribbly Gums

A rich mix of old and young trees in Black Mountain forest

I have noticed that there have been many more features on wildlife than wildpaces lately in the blog, so I shall try to adjust this. First off, this gave a reason to go for a walk in one of the local forests, the 500 ha Black Mountain Nature Reserve, which is only two kilometres from Canberra city centre  The woodland is dominated by two eucalyptus tree species, Scribbly Gum Eucalyptus rossi and Red Stringybark E. macrorhyncha, and the under story is mostly a sparse covering of grasses and short shrubs. The trees provide thousands of cavities for such animals as possums and parrots - especially Crimson Rosellas, while I often see swamp wallabies and echidnas working through the undergrowth.

Wild forest in the foreground - urban high-rise only a mile away

There are numerous tracks to follow through the forest and multiple variations of routes to take. On today's walk I went around the summit and looked down onto the city. And I noticed how, even the city looked green with the street and park trees shining between the buildings.

A zoomed-in view of Canberra city from Black Mountain

Now that it is late summer, some species of eucalypt trees have shed their outer layers of old bark to reveal shiny new skin. The Scribbly Gums do this but not the stringybarks.

This fine old Scribbly Gum has large and small hollows,
 it is a true veteran, yet is still throwing up young branches from its old trunk.

The cast bark lies thick on the ground in some places, giving homes and shelter to all sorts of animals, but it can build up deep enough to become a fire hazard and Canberra, as the bush capital, is well aware of the danger of bush fires. So there are regular burn-offs of the ground cover over the years to prevent such a risk.

Shards of bark lie about the base of the gum trees, their inner surface glowing red in the sunshine

The Scribbly Gum is named after the marks on its bark, which are especially noticeable when the bark is freshly cast. These scribbles are the marks of where a species of moth larvae, Scribbly Gum Moth Ogmograptis scribula, have meandered safely beneath the old bark layer, while munching on the fresh growth immediately below. To find out more on the moth and its larva, click here to a link to the Australian museum website.

The zig-zag trail left by a scribbly gum moth larva - its journey began at the thin end of the trail, where the adult moth had laid her egg. The trail ends at the thick end where the larva emerged and crawled into a crevice to form a cocoon. The  adults emerge in the autumn.