1 Julia Cooke and Ted Edwards, ‘The behaviour of scribbly gum moth larvae Ogmograptis sp. Meyrick (Lepidoptera: Bucculatricidae) in the Australian Capital Territory’, Australian Journal of Entomology, vol. 46, 2007, pp 269–75.
The gum-tree stands by the spring
I peeled its splitting bark
And found the written track
Of a life I could not read.
Judith Weight was inspired to pen these words, intrigued by Nature’s enigmatic graffiti on our smooth-barked gum trees. These scribbles have puzzled biologists and bush walkers up and down Australia’s south-eastern seaboard for generations.
May Gibbs etched these hieroglyphics into the national folklore when she chose them to inspire the font style of the birthday invitations and the strike banners in her 1918 classic Snugglepot and Cuddlepie. A copy of the first edition of this book was a popular choice by the Australian Government for Princess Mary of Denmark on the birth of her first child. Gibbs didn’t have a clue back then about the biological significance of the scribbles she had made famous. At first they were presumed to be the work of beetles, but cursory research by Tom Greaves at CSIRO Entomology in 1934 established that the critter responsible was a very small, and totally uninspiring, moth.
In 1935 the scribbler was given the erudite name Ogmograptis scribula by an ageing English school teacher, Edward Meyrick. Meyrick spent his ‘spare’ time describing and naming a good part of the world’s moth fauna; more than 14,000 species bear scientific names given them by this inspired part-time taxonomist. Each newly named species was meticulously described by Meyrick, so this naturalist was no casual name dropper. His labels have stood the test of time and the scrutiny of modern science.
As a young man, Meyrick visited the Antipodes and taught classics at Sydney Grammar and The King’s School, Parramatta between 1877 and 1886. He returned home shortly after and devoted the leisure moments of his long life to a labour of love—describing a group of moths, large in number but small in size, that entomologists call microlepidoptera because their wings (pteros) are covered in small scales (lepidos).
Just one family of these compact moths, the Oecophoridae, number more than 6000 species in Australia alone. These fauna, whose larvae are mainly leaf-litter munchers, have shaped much of Australia’s soils over eons. They invented the mobile home: oikos being Greek for ‘home’, and phoro meaning ‘carrier’, in recognition of the fact that many species construct and then shelter in these mobile dwellings.
Without doubt Meyrick would have been familiar with the scribbles but not the scribbler during his early days in Australia. But half a century later, by 1935, Meyrick had become the undisputed expert. He was the natural choice to describe the scribbly moth and give it a scientific name. Being a classics scholar helped, and he created around 28,000 scientific moth names such as Ogmograptis scribula, which combines ogmos, Greek for furrow; graptis, Greek for inscribed/painted; and scribula, Latin for writing.
That’s where the story might have ended, but for the confluence of some extraordinary events over the past fifteen years. Why nothing happened to unravel the mystery since 1935 is itself interesting. Putting the question into context, CSIRO believes that there are about 220,000 species of insects in Australia. Around 86,000 enjoy scientific names. For the vast majority, little is known about their biology or role in the environment. O. scribula fits into this category. What’s remarkable is that we are learning more about scribbly moths, but only scratching the surface. Already one species has now blossomed into twelve new species, with more to come. The prediction of 220,000 species down under could be a vast underestimate.
There was no economic issue to prompt further investigation on the scribbly moth. There was no particular scientific question to arouse interest. There was no environmental trigger, just a single species among the many species of moth whose larvae developed under the bark of some smooth gum trees. All the scientific tools were available in 1935 to solve the riddle. What was missing was a catalyst, and that was provided several years ago. A teenager started asking questions.
What has emerged is a fascinating story of forensic taxonomy, combined with some exquisite detective ecology involving a schoolgirl in Canberra, Julia Cooke, and the curiosity of two retired scientists. One of them, Max Day, spent much of his life studying insects but retired thirty years ago—and he’s still at the crease, scoring boundaries, four years short of his century. Max was joined by a retired botanist, Celia Barlow, and a determined taxonomist, Marianne Horak.
This odd ensemble, bolstered by several serving colleagues with complementary skills, has unravelled an amazing story and given us not one, but well over a dozen new species of scribbly gum moths that started a co-evolutionary journey with eucalypts around 70 million years ago. We now know much more about how these moths function in a fabulous demonstration of insect behaviour shaping design, essentially the larval machinery, as the moth larva completes its lonely life cycle in the cork cambial layer, the growth tissue just under the outer bark, of their chosen eucalypt hosts.
Nothing had progressed in our understanding of the scribbles or the biology of its creator since Greaves’ brief 1934 work, not even where the moth fitted into the various candidate families of the large lepidopteran fauna. The close relatives of the moth were not clear to Meyrick, despite his enormous knowledge of these moth families. Indeed, Ian Common, the foremost twentieth-century expert on Australian moths, refused to list the iconic moth in his definitive Moths of Australia (1990). Like Meyrick, Common couldn’t even assign it to a family, something almost unheard of for a named insect; and so this famed insect continued to languish in obscurity.
Only last year, in the delightful children’s book My Little World, a youthful Julia Cooke wrote:
And then upon a smooth-barked tree,
I found the oddest mark.
Like a funny zigzag pencil line,
Scribbled on the bark.
The owner of the tag was gone—
Perhaps it’s very shy?
What sort of thing could make this mark?
And how and when and why?
Gran couldn’t read the writing,
And it made no sense to me.
Could it be an insect code,
Written on the tree?
During a Canberra High School assignment, Cooke helped trigger the sequence of events that has begun to answer the very questions she poses in her poem. Working on a statistical analysis of the population of scribbles at three localities in the Australian Capital Territory, Cooke rightly concluded that there must be more than the one species of moth creating the scribbles. Three distinct scribble ‘dialects’ forced that surprising conclusion on Cooke and her mentor, Ted Edwards. Cooke and Edwards, another retired lepidopteran taxonomist from CSIRO Entomology’s National Insect Collection, published their scribbly gum moth findings in 2007. 1
In about 1990, when I was chief of CSIRO Entomology, Max Day walked into my office. Day had led a very distinguished career as a researcher in the Division (1940–66). He was subsequently on CSIRO’s executive. Then followed a term as the first chief of CSIRO’s Division of Forestry, where his interests in eucalypts were further developed.
Day, then eighty and retired for fifteen years, put a proposition to me this way. ‘My doctor says I might lose my marbles if I don’t exercise my brain. Could I return to the Division and join the distinguished group of Honorary Research Fellows?’ Short of any ready reason to decline his request, I agreed. Day dusted the cobwebs off his neurons and began to do some arcane work on taxonomy of a sap-sucking group of insects.
That task completed, casual discussions with moth taxonomists Marianne Horak and Ted Edwards about the scribbles on neighbouring Black Mountain spiked Day’s interest and reignited his plant–insect interactions skills that had lain dormant for many years. Day cobbled a team of interested players into his scribbly moth network: Horak and Edwards (moth specialists), Celia Barlow (a retired botanist), You Ning Su and Stephen Cameron (a molecular biologist). What emerged has been a sensation even among hardened entomologists.
Many of the key findings have been submitted for publication in an Australian taxonomy journal. The authors could have chosen more prestigious international journals. But this was an Australian story with international ramifications; and so they chose a local but well-respected journal where the paper remains under review.
Eleven new species of scribbly moths have been described, and it’s clear that an even larger number remain undescribed. The close relationship between the various moth species and their eucalypt hosts indicated the moths were also competent taxonomists; they were picky about which species of tree were suitable for depositing their eggs.
However, where the scribbly species fitted into the lepidopteran order remained uncertain. The early larval stages (called instars) are constructed as superb tunnelling machines. They are legless, just a chewing head, a middle and a tail end for discharging the bark cells converted to powdery droppings, or frass. The moult to the final larval stage, when legs first appear, takes place at the exact moment when the cork cambium starts producing cork—except inside the larval track, where callus tissue starts to form. Just how this delicate developmental synchrony between moth and tree was achieved over evolutionary time is a topic for future research.
So for the remainder of its juvenile existence, the last instar larva turns back into its old tunnel, now filled with nutritious callus on which it feeds until fully grown. The mature larva drops to the ground and pupates in the surface debris, eventually emerging as a weakly flying moth to repeat the annual cycle. Comparison with its sister group of moths in South Africa suggests that the co-evolutionary journey commenced 70 million years ago, before Africa drifted away from Australia and the rest of Gondwana. That means the moth’s ancestors had 70 million annual life cycles to perfect the relationship.
The larval phase is confined to a precise position in the cork cambial layer such that when the bark completes its annual shedding, the larval track is recorded on the outer trunk of the gum tree and on the shed bark. The zigzags also fit within the edges of the shed bark. Just how the larva can detect where these abscissal boundaries will form remains a mystery. Clearly, these edges must be predetermined before the bark commences the shedding process. It is not obvious that the moth is harming the tree; nor is it apparent that the tree gains anything from this relationship.
There is another group of these moths whose larvae work the inner vascular cambial layer. Their tunnels are not lost with the shed bark, but become embedded in the wood as the tree continues to grow and appear as raised scars on the surface of smooth-barked eucalypts. These are the ghost scribbly moths. I now know the origin of the ghost scribbles in my blackbutt dining-room floor.
The thickened portion of the scribble is not a simple mine, like the wider zigzagging initial phase, but is filled with callus. This led Horak, Day, Barlow and colleagues to realise that they were looking at a group of taxa with a two-phase life cycle—miners and callus feeders. The field biology finally allowed Horak to work out the evolutionary relationships of this group of scribblers and other members of lepidoptera, and confirm the hitherto tentative referral of the scribbly moths to the family Bucculatricidae. The related ghost scribbly moths had been wrongly ascribed to another family. Preliminary molecular and morphological evidence now confirms that these also belong to the often gall-forming Bucculatricidae.
It’s a shame that Judith Wright and Ian Common did not live long enough to learn more about the ‘life I could not read’. Julia Cooke has just completed a PhD at Macquarie University on insect–plant relations and has a bright career ahead. And we are all blessed that Max Day has ‘kept his marbles’ long enough to lead the field work and inspire the team to unravel the biology of the scribble moths: all hard slog in the midday sun, cutting bark to examine live scribbles, collecting larvae at different stages of development, searching for pupae (the resting stage between larva and adult), matching development with seasons, and moth species with eucalypt species.
There are some morals to this story. Fortuitous encounters brought the team together to complete the zigzag jigsaw puzzle, or at least to assemble enough of the pieces to enable us to grasp the bigger picture confidently. Unfortunately, no amount of luck or ‘fortuity’ will allow us to believe this story could be repeated.
Trends in modern research facilities see the traditional field workers, once equipped with four-wheel-drive vehicles, replaced with desk-bound ‘meta-scientists’—geeks who study earlier studies. Computers and their operators, connected like Siamese twins, breathe rarefied air as they spend their working hours mining the tailings of existing data from already published reports.
That’s perhaps a bit of an exaggeration, but let me defend my perception by drilling a bit deeper into the scribbly moth story. It was only possible by the pooling of a suite of skills—ecology, classical taxonomy and molecular biology. Retirees Day and Barlow sorted out what was happening in the field, who did what and where, and how the plant responded to the presence of the larva in producing the callus within the larval tunnel. Horak, assisted by retiree Edwards, did the painstaking morphological investigation. Her work not only elucidated the phylogenetic relations between the many taxa; based on the field work and microscopy, Horak was also able to link larval forms with function and behaviour—the legless larvae working as a well-designed mole, the legged larvae harvesting the callus tissues, and the adult female well tooled to lay eggs. Preliminary molecular work on DNA confirmed and finetuned the evolutionary relationships.
Horak and Edwards are unlikely to be replaced by similarly skilled taxonomists. Their discipline is deemed passé. Max Day, although ninety-six, might soldier on and outlast all of us. To the extent that researchers such as Horak are being replaced at all in a world where funding for frontline science is shrinking in absolute terms, the new emphasis is on modellers and molecular biologists; these are the favoured castes. In particular, there is a push to fund and expand a novel field of molecular identification called ‘barcoding’ at the expense of traditional taxonomy.
Molecular barcoding, as the name suggests, comes from the familiar technique where a unique set of bars allows rapid scanning at supermarket checkouts. It also provides huge management benefits for inventory, ordering, stocktaking and so on. The molecular version has also become a valuable tool in taxonomy and biodiversity studies, though it is far from infallible. It helps detect cryptic species—where the taxa are genetically separate but morphologically indistinguishable. It also allows the association of the often very different-looking larva, even eggs, with the adult as they all have the same genetic material. Molecular barcoding will enable rapid identification of a taxa, for quarantine say or pest ID purposes. It is not just a valuable tool in taxonomy; clearly it serves other useful purposes and needs to develop as a mature discipline.
However, if barcoding capability is seen as a substitute for classical taxonomy, whose essential role we saw in the scribbly moth story, it would be as destructive as its use in the supermarket, if the tin can carried no other label beyond the bar code. Whether it is beans or jam or soup, the information on the label—its nutrient content and so on—is vital for the customer.
A visit to some of our national labs nowadays reminds me of Jonathan Swift’s satire on science in Gulliver’s Travels (1726):
About forty years ago, certain persons went up to Laputa, either upon business or diversion, and, after five months continuance, came back with a very little smattering in mathematics, but full of volatile spirits acquired in that airy region: that these persons, upon their return, began to dislike the management of every thing below, and fell into schemes of putting all arts, sciences, languages, and mechanics, upon a new foot. To this end, they procured a royal patent for erecting an academy of projectors [i.e. scientists] in Lagado; and the humour prevailed so strongly among the people, that there is not a town of any consequence in the kingdom without such an academy. In these colleges the professors contrive new rules and methods of agriculture and building, and new instruments, and tools for all trades and manufactures; whereby, as they undertake, one man shall do the work of ten; a palace may be built in a week, of materials so durable as to last for ever without repairing. All the fruits of the earth shall come to maturity at whatever season we think fit to choose, and increase a hundred fold more than they do at present; with innumerable other happy proposals. The only inconvenience is, that none of these projects are yet brought to perfection; and in the mean time, the whole country lies miserably waste, the houses in ruins, and the people without food or clothes. By all which, instead of being discouraged, they are fifty times more violently bent upon prosecuting their schemes, driven equally on by hope and despair.
Swift’s Gulliver then proceeds to describe the antics of some of the ‘projectors’. His satire presupposes the utilitarian value of science as its sole and unchallenged justification. Swift foreshadowed scientific modernism—harnessing nature for the material benefit of humanity. His cynicism towards the various projects in the academy was prompted by their impracticality, not their irrelevance. For example, the solar energy projector had ‘been eight years upon a project for extracting sunbeams out of cucumbers, which were to be put in phials hermetically sealed, and let out to warm the air in raw inclement summers’.
Gulliver’s condescending account had another modern ring. Referring to the sunbeam harvester, he recorded, ‘I made him a small present, for my lord had furnished me with money on purpose, because he knew their practice of begging from all who go to see them.’
Wherever we stand in the spectrum of modernism (controlling nature for our benefit) through to postmodernism (living with nature), the scribbly moth story gives us cause to pause and reflect about what it is we want from our scientists. Are they mere handmaids of industry? Scribbly moths pose no economic threat nor opportunity to ‘justify’ the research. The value of the knowledge is cultural; it stems from our desire to understand the natural world around us. It’s what Ed Wilson, one of the world’s leading biologists, calls ‘biophilia’, a uniquely human attribute.
The moth story so far poses more questions than it answers; yet we are enriched. There may be twenty species when we thought we had only one. We know their evolutionary relatives, something that flummoxed Meyrick and Common because the biology was missing. We see finely tuned machines redesigned over each life cycle to meet changing needs. We find a schoolgirl and retirees energising each other. None of this is mainstream science in today’s Australia.
A resurrected Judith Wright might now muse:
The gum-tree stands by the spring
I peeled its splitting bark
And found the written track
Of a life I now could read.
Extract from ‘Scribbly Gum’, 1955, by Judith Wright, from A Human Pattern: Selected Poems, ETT Imprint, Sydney, 2010.
Extract from ‘My Little World’ by Julia Cooke and Marjorie Crosby-Fairall. Text © Julia Cooke, 2011. First published by Omnibus Books, a Division of Scholastic Australia Pty Limited 2011. Reproduced by permission of Scholastic Australia Pty Limited 2011.
© Max Whitten 2012