The scribbles on scribbly gums have intrigued people since the first European settlement in Australia.
The gum-tree stands by the spring.
I peeled its splitting bark
and found the written track
of a life I could not read.
(From A Human Pattern: Selected Poems by Judith Wright. Used with permission.)
Many Australians, especially those on the east coast, are aware of the 'scribbles' found on some eucalypt trees – often called scribbly gums. For years they have intrigued bushwalkers and writers.
These distinctive marks decorated the trunks of some of the first gum tree species described by European botanists at Sydney Cove in the late 1700s.
Scribbly gums have found their way into the poems of Judith Wright and the illustrations of May Gibbs' much loved classic The Gumnut Babies.
Despite their status as an icon of the Australian bush, very little was known about the cause of the distinctive 'scribbles'. At first, it was thought that they were caused by beetle larvae. Some people doubted whether they were caused by insects.
It is now apparent that different scribbly gum moths produce different scribbles.
Revealing the culprit
In the mid-1930s, Mr Tom Greaves from CSIRO Entomology discovered the cause of the scribble. He discovered that the larvae of a very small moth were producing the markings on the bark of snow gums in the Brindabella Ranges west of Canberra.
Our knowledge on scribbly gum moths languished for around seventy years. In 1999, Miss Julia Cooke, a student from Canberra, investigated the cause of the scribbles, as part of her entry in the BHP Science Prize. She compared the scribbles on different species of eucalypts and came to the conclusion that they were different and suggested there might be more than one species of moth. However, nothing was known about the biology of the moth.
In 2005, CSIRO scientists, Dr Max Day and Dr Marianne Horak, trapped two species of moth from the local Canberra scribbly gum Eucalyptus rossii and identified two distinct scribble tracks thus confirming that there is more than one species of moth that creates scribble patterns in trees.
We now know that there are at least six types of scribble, at least 20 species of eucalypts with scribbles and that there are several species of moths producing scribbles. There are many more to be discovered.
Find out about Scribbly gums: interpreting their scribbles.
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