For my twenty-first birthday, my parents gave me a gum tree seedling. It was a young Eucalyptus rossii and we planted it in the their front garden. It was only about 50cm high. The species was significant because I had conducted a high school project on this species, or rather on the moth larvae that mine under the bark of the trees. Scribbly gums moths lay their eggs on the bark and the grubs burrow into the bark and feed in the cambial layer. You can’t see them. But some time later, perhaps the following year, the outer bark sloughs off and the feeding tracks made by the larvae are revealed. These tracks show that the larvae zig-zag up or down the trunk in distinctive ways, which is why their tracks are called scribbles. For my school project I measured thousands of these tracks to learn more about the larvae behaviour, and published my findings here.
But back to the tree my parents gave me. It has thrived and grown and at just over 15 years old, it is now about 6 m tall (thanks to my folks!). But the tree has never had a scribble on it’s bark.
Scribbles are not usually found on narrow trunks so in the early years we were not surprised that we didn’t find any. Also the moths only have a wingspan of 0.5 cm, and there are no E. rossii trees near my parents house, so we wondered if the moths could get there on their own. Perhaps we would need to collect some leaf littler at the time the larvae pupate and bring home?
But this morning Mum emailed me with some exciting pictures. On the way back from her morning walk she noticed that the tree had recently shed last year’s bark. She checked the new bark and found scribbles! Our Eucalyptus rossii had three scribbles! The tree was big enough and the moths had found their way there all on their own! I love it that Mum raced for her camera to send me picture straight away.
And the timing was perfect… it was my birthday this week.
Photos: Pam Cooke.