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The biology of Hickmania troglodytes, the Tasmanian Cave

N. E. Doran,' A. M. M. Richardson^ and R. Swain' 'Zoology Department, University of Tasmania, G.P.O. Box 252-05, Hobart, Tasmania 7001

Hickmania troglodytes, the Tasmanian Cave and transition zones of caves, which are Spider (Fig. 1), is of considerable phylogenetic believed to have ensured its survival during importance and zoogeographic interest. It the climatic fluctuations of the Pleistocene belongs to a relict group of with a (Goede 1967). scattered v^'orld distribution that combines Downloaded from http://meridian.allenpress.com/rrimo/book/chapter-pdf/2643144/rzsnsw_1999_052.pdf by guest on 28 September 2021 Despite the phylogenetic and zoogeographic characteristics more commonly divided between significance of H. troglodytes, and its ecological the primitive and advanced spider infra- importance as a major predator in caves, little orders. Endemic to Tasmania, the species is has been recorded about its life history and the type and sole representative of its , behaviour. In the course of a long-term (1991 and its closest relatives are found in Chile and to present day) monitoring program within Argentina. an undisturbed cave environment at Mole The Tasmanian Cave Spider was first named Creek, Tasmania, and through supplementary as Theridion troglodytes by Higgins and Petterd studies of caves throughout the state, we have in 1883, one of the earliest and most made many observations of H. troglodytes and prominent examples of cave fauna recorded now know that it displays many unusual for Tasmania. The species has undergone a characteristics in its life history. variety of changes in name and taxonomic For the first time, field observations have placement since then, culminating with been made of courtship and mating behaviour Gertsch's designation of the genus Hickmania in this species, and for the "austrochiloid" in 1958. This was in turn placed within the group as a whole. The majority of courting by Forster, Platnick and Gray and mating events occur from late winter in 1987. to spring (August to October), in contrast to Hickmania troglodytes is the largest spider the late spring and summer matings of most in Tasmania, with a legspan of up to 18 cm Tasmanian spiders. Courtship is ritualized, (Figs 1 and 3). There is an obvious sexual and may last for hours. The mating hold is dimorphism, with males possessing more precise, with the male using the specialized slender bodies, longer legs, and a distinct crook in the metatarsi of his second leg curve in the metatarsi of the second leg pair to pin the cheliceral region of the female. jair. The species builds a large and obvious Her legs are in turn immobilized and pushed lorizontal sheet web, which may be more than back by his first leg pair (a more detailed a metre across. The spider hangs beneath account of mating behaviour and the repro- its web, attacking prey that fall into it from ductive cycle is in preparation for publication above. Females produce large pear-shaped egg elsewhere). sacs of tightly woven white silk, approximately 4-f cm high and 2.5 cm wide (Fig. 2). Egg-sac construction is an involved process and the finished structure is unusual, with a The Cave Spider is widely distributed rigid thimble-hke egg mass hanging separate throughout Tasmania, particularly where lime- from the silk walls. This "thermos-like" structure stone, dolomite or other karst and pseudo- may serve to buffer the eggs and young from karst caves and features are found. As a external fluctuations in temperature and troglophile, however, the species is not an humidity, and to isolate them from contamin- obligate cave dweller, and — with slight ants that settle in the silk. The silk in turn behavioural modifications — can also be found appears to be exceptionally resistant to fungal in any suitably cool, dark, damp and sheltered and bacterial degradation, as discarded egg- surface habitats, including hollow logs in rain sacs can persist for years in caves while all forest, the underside of bridges, river banks, other organic materials are rapidly over-run culverts, mine shafts, and even the occasional by fungus and mould. Surface dwelling H. shower recess. Despite this, the primary troglodytes can even camouflage their egg-sacs habitat for the species remains the entrance by implanting fragments of wet rotting wood

Pp. 330-32 in The Other 99%. The Conservation and Biodiversity of Invertebrates ed by Winston Ponder and Daniel Lunney, 1999. Transactions of the Royal Zoological Society of New South Wales, Mosman 2088. Downloaded from http://meridian.allenpress.com/rrimo/book/chapter-pdf/2643144/rzsnsw_1999_052.pdf by guest on 28 September 2021

Figure 1. Adult female H. troglodytes against 1 cm scale, Figure 2. Adult female H. troglodytes guarding an egg-sac dorsal view (photo: Niall Doran), constructed in captivity, lateral view (photo: Kevin Doran).

by a marked increase in condensation on the outer surface of the egg-sac, as conditions vary with seasonal changes in air flow through a cave. Whatever the stimulus, emergence periods and timing appear to vary between caves, and even between regions within a cave. The mobility and distribution of the spiders varies according to age/size, sex, and repro- ductive status. Males will wander large distances to find females, while females may in turn wander between those areas that are more productive for food sources and those that are more suited to nurturing egg-sacs. Spiders will move in response to seasonal fluctuations in cave entrances, whether in Figure 3. Adult female H. troglodytes on the hand of the direct response to the changing conditions or senior author, Honeycomb Cave (photo: Kevin Doran). the changes that these impose on their prey. Juvenile spiders tend to penetrate deeper into cave environments than adults, probably due directly into the silk surface with no ill effect. to a mixture of differences in environmental Whether this is due to the physical structure tolerances, requirements, competition and of the silk, a low nutrient content, or direct predation. activity of antibiotic materials is currently under investigation. A single intermoult period for H. troglodytes may last for over two years. Given their The young emerge from the egg-sac eight sedentary lifestyle and slow growth, these large to ten months after laying, well in excess of spiders may live for decades, placing them the usual spider emergence time of four to among the longest lived of the advanced eight weeks. Despite this, anecdotal evidence Araneae. suggests that the emerging young may be less well developed than the young of more Beyond the significance of H. troglodytes as advanced spiders. Emergence may be triggered discussed above, the spider has a potentially

June 1999 The Other 99%. The Conservation and Biodiversity of Invertebrates 331 important role in cave (and cave fauna) While Hickmania troglodytes is not a threat- conservation. Tasmania has many caves, and, ened species per se, its sedentary nature, size, despite the sparse and barren appearance of longevity, and numbers present a potentially such environments, these have been shown to useful long-term tool for the monitoring contain a rich and diverse invertebrate fauna of cave fauna and karst areas, and for the (Eberhard et al. 1991). Unfortunately, the evaluation of remedial and management sparse, small and cryptic nature of this fauna activities in such environments. As such, it often makes regular monitoring programs may play an important role in future land untenable, and sampling programs may even management decisions and planning for karst be detrimental given the fragile nature of cave areas, and can provide valuable indirect environments and the population dynamics of information on the health of cave ecosystems. the cavernicolous invertebrates they contain Indeed, the Tasmanian Cave Spider is already (Slaney and Weinstein 1997). being used for just such purposes, and in this way is helping protect the rich invertebrate Despite their apparent isolation from diversity of Tasmania's caves. the surface, cave environments are directly dependent upon and affected by surface events. Land-use activities impacting on ground REFERENCES Downloaded from http://meridian.allenpress.com/rrimo/book/chapter-pdf/2643144/rzsnsw_1999_052.pdf by guest on 28 September 2021 and surface water quality and levels, humidity, Doran, N. E., Eberhard, S. M., Richardson, A. M. M. air movement and temperature and the and Swain, R., 1997. Invertebrate biodiversity and provision of various sources of food (including conservation in Tasmanian caves. Memoirs of the stream-borne detritus and entrance zone Museum of Victoria 56: 649-53. vegetation) can all have immediate and devas- Eberhard, S. M., (in press). Cave fauna management and tating impacts on underground ecosystems. monitoring at Ida Bay, Tasmania. Tasmanian Parks and While clearing and quarrying are two Wildlife Service Nature Conservation Report. particularly important issues with regard to Eberhard, S. M., Richardson, A. M. M. and Swain, R., cave conservation, the increase in recreational 1991. The Invertebrate Cave Fauna of Tasmania. cave use is also of concern (Eberhard et al. Zoology Department: University of Tasmania. 1991; Doran et al. 1997; Richardson et al. Forster, R. R., Platnick, N. I. and Gray, M. R., 1987. 1997; Eberhard, in press; our unpubl. data). A review of the spider super-families Hypochiloidea and Austrochiloidea (Araneae, ). The conservation status of Tasmanian caves Bulletin of the American Museum of Natural History 185 is variable. Some important cave systems, (article 1): 1-116. whether by default or design, fall within Gertsch, W. J., 1958. The spider family Hypochilidae. recognized parks and reserves, but many American Museum Novitates 1912: 1-28. do not. Some reserves are of insufficient size Goede, A., 1967. Tasmanian cave fauna: character and to fully protect the surrounding catchments distribution. Helictite 5: 71-86. or karst bodies, and so the health of the Higgins, E. T. and Petterd, W. F., 1883. Description of a caves may remain under threat despite their new cave-inhabiting spider, together with notes on protected status. While official codes of mammalian remains from a recently discovered cave practice and notification systems exist and in the Chudleigh district. Papers and Proceedings of incorporate cave issues for such industries as the Royal Society of Tasmania for 1883: 191-92. forestry, no enforcible codes exist for mining Richardson, A. M. M., Doran, N. E., Eberhard, S. M. and and no codes exist for agricultural practices. Swain, R., 1997. Bioconservation and Tasmanian Ten invertebrate cave species are recognized Cave Fauna. Pp. 17-24 in Cave and Karst Management under the Tasmanian Threatened Species in Australasia 11: proceedings of the eleventh Australasian conference on cave and karst management, Cowrie Park, Protection Act (1993), and voluntary minimum Tasmania, May 1995. impact caving codes are also in place. In many instances, however, the strength and Slaney, D. P and Weinstein, P., 1997. Conservation of cave fauna: more than just bats. Memoirs of the effectiveness of these codes and guidelines Museum of Victoria 56: 591-96. remain untested, many issues remain to be acted upon, and our information base is still inadequate.

332 The Other 99%. The Conservation and Biodiversity of Invertebrates June 1999