A scribbly gum moth - one of several species of these tiny moths that have now been found.

Scribbly gums: interpreting their scribbles

CSIRO researchers are the first to uncover the lifecycle of the moth responsible for iconic scribbles on Australian eucalypts.

• 7 September 2006 | Updated 14 October 2011

• Background
• Recent discoveries

Background

The 'scribbles' on scribbly gums have intrigued people since the days of early European settlement in Australia. Despite their status as an icon of the Australian bush, until recently very little was known about the cause of these distinctive 'scribbles'.

In the mid-1930s CSIRO scientist Mr Tom Greaves discovered that the cause of the 'scribbles' was the larva of a very small moth.

Adult moths were sent to England for identification and it was found they were from a new genus, which was given the name Ogmograptis and the moth was named O. scribula.

By the late 1990s, scribbles had been found on about 20 species of eucalypts. It is now known that there are more than half a dozen species of Ogmograptis and at least five distinct scribble patterns, suggesting that different moths produce different scribbles. 

Although most of these eucalypt species have been planted in the Australian Botanic Gardens (ANBG) in Canberra, only the local Eucalyptus rossii and its close relative E. racemosa 'get scribbled on'.  This would indicate that the scribbly gum moth species associated with the eucalypt species from other regions in Australia are not found in Canberra.  So only the local gums with the local moths are scribbled on.

Recent discoveries

In the summer of 2005, CSIRO Entomology Emeritus Fellow, Dr Max Day and a group of interested helpers undertook a search for the moth larvae. They eventually found and captured the tiny larvae and pupae of a scribbly gum moth on a local Canberra scribbly gum. The moths, when they emerged, were not O. scribula but a new species, yet to be described and named.

Scribbles from one species of scribbly gum moth on the trunk of a eucalypt.

The discovery of larvae and pupae enabled the scientists to describe for the first time the life cycle of one species of scribbly gum moth. Eggs are laid in autumn (i.e. April and May) and the larvae develop in the bark through winter. The scribble patterns are caused when they feed on tissues just below the epidermal cells in the tree trunk.

In early summer, the larvae pupate at the base of the tree. The tiny adults that emerge in autumn are only a few millimetres long.

Dr Marianne Horak and Dr Ted Edwards have now identified four species of moth and two distinct types of scribbles from the local Canberra scribbly gum Eucalyptus rossii. This is added evidence that individual moth species make different scribble patterns.

This also confirms that there is more than one species of moth that creates scribble patterns in trees.

Scientists are keen to discover more on the natural history of these moths as there are still many questions to be answered, in linking moth species with their scribbles.

Find out about The saga of scribbly gum moths.