Scribbly Gum Moth Tunnels

The scribbly gum moth larvae bore a meandering tunnel through the eucalypt tree’s bark at the level of the future cork cambium, first in long irregular loops and later in a more regular zigzag which is doubled up after a narrow turning loop.

When the cork cambium starts to produce cork to shed the outer bark it produces scar tissue in response to the feeding of the caterpillar, filling the doubled up part of the larval tunnel with highly nutritious, thin-walled cells.

These replacement cells are ideal food for the caterpillar which moults into its final life stage with legs, turns around and eats its way back along the way it has come. It now grows rapidly to maturity and leaves the tree to spin a cocoon at its base, where it pupates.

Not long after the caterpillar leaves the tree, the bark cracks off and exposes the iconic scribbles beneath.

https://csiropedia.csiro.au/scribbly-gum-moths/