What turns glow-worms on? Baseline monitoring of the Tasmanian glow-worm and other cave fauna in Exit and Mystery Creek caves
Email: Michael.Driessen@dpipwe.tas.gov.au
Abstract
Exit Cave and Mystery Creek Cave in the Ida Bay karst system in south-east Tasmania contain a diverse and significant cave fauna. The most superlative faunal feature of these caves is the light displays by the Tasmanian Glow-worm Arachnocampa tasmaniensis. These displays have been recognised as a world heritage value under the criterion relating to outstanding natural phenomena. Remarkably, there has been no previous study on the ecology of the Tasmanian glow-worm. Glow-worms and other cave fauna were monitored monthly for 24 months to obtain information on their ecology and to establish baseline population data. A strong seasonal pattern was found for glow-worms, with pupae and adults most common in spring and summer. The increase in numbers of pupae and adults coincided with an increase in the number of prey caught in silk threads produced by the larvae. Larvae were present throughout the year but the number glowing varied both seasonally and spatially. In Mystery Creek Cave, the number of larvae glowing was generally highest during summer and autumn, and lowest in winter and early spring. In Exit Cave, there was no consistent seasonal pattern in the number of larvae glowing among sites, and overall there was less variation between monthly counts than at Mystery Creek Cave. This difference in seasonal patterns between the two caves may be due to a difference in cave climate, with Mystery Creek Cave possibly experiencing a greater drying out of the cave air in winter than Exit Cave. Monthly counts of cave crickets and other cave fauna, which were common in Exit Cave and uncommon in Mystery Creek Cave, revealed few interpretable patterns. The only consistent pattern observed was in the part of Exit Cave known as the ‘wind tunnel’ where cave cricket and cave beetle numbers were high during the warmer months and low during the cooler months. This is likely to be a response to the winter effect in that part of Exit Cave. Further information on this research is available in Driessen, M.M. (2009). “Enhancing the conservation of the Tasmanian Glow-worm (Arachnocampa tasmaniensis) by monitoring seasonal changes in light displays and life stages”. Journal of Insect Conservation 14: 65–75, and in Driessen, M.M. (2009) “Baseline monitoring of the Tasmanian Glow-worm and other cave fauna”. Nature Conservation Report 09/02, Department of primary Industries and Water, Tasmania. Both articles are available from the author.