Midnight is generally a good time to be tucked up in bed, sound asleep. But on this particular night, I find myself disembarking from a car at the edge of Springbrook National Park. Stifling a yawn, I throw my camera and tripod across my shoulder and hurry after my companions.
Our pencil-light torches pick out a well-worn path leading down to the rocky overhang known as 'Natural Bridge'. The overhang formed over millions of years, as a stream flowed over layers of volcanic rock. Today it sports a dramatic waterfall that plunges 10 or so metres into a crystal clear pool. It's a popular south-east Queensland tourist spot. But it's not only the waterfall that attracts tourists.
As we descend the steps that take us behind the waterfall, we're transported into the inky blackness of a shallow cavern. Moisture drips from the ceiling, and somewhere to our right, a colony of bats chatters and flaps through the darkness. But as our eyes adjust, a spectacle rivalling that of the Milky Way reveals itself. All around us, in the cracks and crevices of the cavern ceiling and walls, stretches a galaxy of tiny blue-green lights.
Switching on a head-lamp, University of Queensland PhD student, Claire Baker, studies one of the wall crevices. Ushering me nearer, she points out the source of one blue-green light. Suspended in a 'web' of sticky silk threads is a glow-worm - or more precisely, the glowing maggot of a mosquito-like fly.
The six million dollar glow worm
While maggots may seem an unlikely tourist attraction, bioluminescent glow-worms bring in over six million dollars for Australian tourist operators each year. The Natural Bridge colony alone attracts over 300 tourists a night. Despite this popularity, suprisingly little is known about the insects, leading to fears that increasing tourism could unwittingly impact on their survival.
To prevent this, Claire has spent the last two years collecting and studying glow-worms in the rainforests, caves and abandoned gold mines of Queensland, New South Wales, Victoria and Tasmania. Her work has provided some interesting insights into the biology, species diversity and distribution of these fascinating insects.
Only three glow-worm species have been described in Australia: Arachnocampa flava, which is endemic to Queensland, A. richardsae, found in New South Wales and A. tasmaniensis in Tasmania. The name 'Arachnocampa' literally means 'spider grub'- a reference to the web of silk threads that glow-worms use to capture prey.
This silk web, known as a 'snare', is made up of a mucus tube, in which the glow-worm resides, bracing threads, which suspend the glow-worm from its substrate, and 'fishing lines', which hang vertically beneath the mucus tube. Fishing lines can reach up to 40cm in length if undisturbed, and are studded with globular secretions of mucus to immobilise the insects that blunder into them. They look fragile, yet entangled in them Claire has found large insects like cockroaches and beetles. Generally though, smaller insects such as Chironomids (midges), Psychodids (tiny black flies), Phorids (hunchback flies) and other small fly species, are ensnared.
When night falls, glow-worms lure insects into their fishing lines using their bioluminescent taillight. The blue-green light is produced by a chemical reaction between luciferin - a waste product produced by the glow-worm - and the enzyme luciferase, in the presence of oxygen and a form of energy known as ATP (adenosine triphosphate). When an insect is caught, the glow-worm reels its catch upwards using its mouthparts, and attaches it to the mucus tube to prevent escape.
What Claire found
Most of Claire's research so far has focused on the Queensland glow-worm Arachnocampa flava. Claire has raised many of these larvae in the laboratory, in special incubators that maintain a balmy 98 per cent humidity and 230C. Within the incubators, the larvae are housed in clear plastic containers, set up in such a way that the glow-worms experience conditions almost identical to those in their natural environment. To complete the simulation, Claire feeds her larvae two tiny fruit flies (Drosophila melanogaster) a week, by carefully placing anaesthetised flies into their snares.
Claire's work has shown that A. flava larvae live between five and 12 months and go through a series of four moults. The delicate 'first instars' are about three millimetres long and transparent, but reach about four centimetres in length by the 'fifth instar' stage. When a larva is ready to pupate, the mucus tube hardens around it and the adult develops over about seven days. This transformation is similar to that of a caterpillar into a butterfly.
Just before the adult flies emerge from their pupal cases, Claire transfers the cases to a sealed jar containing damp cotton wool. The adult flies, which look a bit like mosquitoes, usually mate as soon as they emerge, and mating can last for more than seven hours! The females then deposit their eggs on the cotton wool.
In the wild, female flies are often greeted by a gathering of eager males jostling for her attention. Both sexes are poor fliers, so females lay their eggs - around 130 of them - within or near the original colony. The adults die soon after the eggs are laid, but after eight or nine days the first instar larvae hatch and begin a new cycle. As the young larvae are very sensitive to cold, dry conditions, they establish themselves near tiny cracks or seepage spots, which they can retreat into if conditions deteriorate.
While the Queensland glow-worm, A. flava, prefers a relatively warm temperature of around 230C, in Tasmania and Victoria, the most spectacular glow-worm colonies are found in caves or old mines where conditions are moist, but a lot cooler. Claire says one colony surviving in an alpine cave at Mt Buffalo in Victoria is significant for a number of reasons.
"It appears that the rainforest used to extend up Mt Buffalo and that the glow-worms remained after the rainforest retracted. Normally the area would be too cold and dry to sustain a glow-worm population, but the cave protects it from the elements," she says.
"This population and other populations like it, could be instrumental in investigating the biogeography of the region and perhaps providing insights into the history of rainforest expansion and contraction within Australia."
Claire's research also suggests that the alpine cave colony is a new species, with close links to the famous New Zealand glow-worms, A. luminosa.
"Based on physical characteristics, the Mount Buffalo population is more closely related to the Tasmanian and New Zealand species, than those along the eastern coastlines of Queensland, New South Wales and Victoria," she says.
"The population is currently being described as a new species, which has implications for conservation, due to its restricted and isolated habitat."
Claire estimates that there are up to a dozen species of glow-worm in Australia and is currently identifying and describing the physical characteristics of larvae she collected from 38 populations around the country - many of which were isolated and previously undocumented. These physical descriptions will be supplemented with genetic information later.
As well as providing new information that will enhance the understanding of Australian glow-worms and their conservation needs, Claire's findings will help tour operators and parks and wildlife managers lessen the impact of tourism on glow-worms, while optimising the visitors' experience.
Claire has also prepared tourist information pamphlets outlining glow-worm biology and factors that affect the insects. For example, she has found that glow-worms are sensitive to torchlight and will switch off their bioluminescence for up to 15 minutes if disturbed. Smoke from fires or cigarettes, and insect repellent, also affect glow-worms and their prey.
In the future, Claire hopes to develop management guidelines for Australian regulatory agencies and tour operators, to ensure the longevity of glow-worm populations and accommodate the needs of industry regulators and tour operators.
"Glow worms are a unique and potentially important insect, so I hope my research can be used as the basis for management and long-term conservation."
More about Claire Baker's research
Fireflies and glow-worms at The Living Museum
About bioluminescence or glowing in the dark
Get the facts about glow-worms from Lamington National Park
The Blue Mountains info page tells all about the Glow Worm Tunnel area of Wollemi National Park
More info on the Glow Worm Tunnel from the Lithgow Tourism Foundation
A set of photographs of scenes near the Glow Worm Tunnel
Claire Baker's project is funded by the CRC for Sustainable Tourism, Aries Tours, Forest of Dreams, Springbrook Tour Operators, and the Queensland Parks and Wildlife Service. Claire would also like to thank Dave Chitty from Adventure Tours, Mt Buffalo, Victoria and Robyn, Glen and Luke from Warburton Wilderness tours, Victoria.