Tasmanian Cave Spider
Distribution:Hickmania troglodytes is confined to Tasmania, where it is widely distributed. It is especially common in areas characterised by underground drainage and cave systems, where large populations may be seen in cave entrance and twilight zones. However, it can be found in many dark, cool, sheltered situations, ranging from hollow logs to the undersides of bridges (TAS).
This species is the sole representative of the spider subfamily Hickmaniinae, known only from Tasmania. It is a relict species, last of an old Gondwanan lineage and its nearest relatives are found in South America. This species is large, with a body length of 13 to 20 mm and a leg-span of up to 180 mm; it weaves a sheet web which may be more than a metre across. Males are smaller and longer-legged than females and have a distinct kink-like curve near the end of each second leg. on each side. The carapace is reddish brown and the abdomen is dull, dark greyish brown. These spiders retain the primitive pattern of four abdominal breathing organs, called book lungs and seen as four light patches on the underside of the abdomen.
Ecology/Way of Life:
These spiders hang by their long legs from the underside of the web, waiting for prey animals that jump, fly or fall into the vast cribellate silk sheet. Its prey includes cave crickets, beetles, flies, spiders and millipedes. Courtship and mating takes place from late winter to spring. The male plucks at the web and, on contacting the female, beats his long front legs against her, alternating with pauses or retreats. This ritualised communication and pacifying activity may be repeated for over 5 hours. The aim is to grip the female's head in the specialised kink on the metatarsal segment of the second legs and pin her fangs apart so that mating can occur safely. The egg sacs are large (about 40 by 25 mm) and pear-shaped. Their structure is unusual. Within the thick, white outer silk walls, the eggs lie enclosed in a rigid, thimble-like structure, which is suspended so that it doesn't touch the outer wall. This "thermos-like" structure may buffer the eggs against climatic changes and contaminants - the silk also seems very resistant to attack by fungi and bacteria. The female guards her egg sacs, and females living outside caves usually disguise their sacs with fragments of wet, rotting wood. Spiderlings emerge from the sacs after 8 to 10 months, an unusually long time, and disperse within a month. The life-span of these spiders is also long, and may prove to last more than several decades.
Interaction with Humans/Threats:
Hickmania troglodytes is significant ecologically as a major predator in caves. It is also important both as a relict species whose nearest relatives are in South America and as a species showing some of the primitive features typical of the earliest araneomorphs (spiders in which the jaws open and close sideways). It is an icon species for faunal conservation in Tasmania, especially in relation to the management of caves.
Described by E.T. Higgins and W. F. Petterd in 1884; the genus name honours Vernon Victor Hickman, the eminent Tasmanian zoologist and specialist on Australian spiders; the species name is based on the Greek: troglodytes = a hole-dweller.
Doran, N.E., Richardson, A.M.M. and Swain, R. (1999). The Biology of Hickmania troglodytes, the Tasmanian Cave Spider. Pp. 330-332. In The Other 99%. The Conservation and Biodiversity of Invertebrates. W. Ponder and D. Lunney (eds). Transactions of the Royal Society of New South Wales.
Doran, N.E., Kiernan, K., Swain, R. and Richardson, A.M.M. (1999). Hickmania troglodytes, the Tasmanian cave spider, and its potential role in cave management. Journal of Insect Conservation 3: 257-262. see also
Doran, N.E., Richardson, A.M.M. and Swain, R. The reproductive behaviour of the Tasmanian cave spider, Hickmania troglodytes (Araneae: Austrochilidae). Zoological Society of London 253: 405-418.
Forster, R.R., Platnick, N.I. and Gray, M.R. (1987). A review of the spider Superfamilies Hypochiloidea and Austrochiloidea (Araneae, Araneomorphae). Bulletin of the American Museum of Natural History 185 (1):1-116.
Hickman, V.V. (1967). Some Common Spiders of Tasmania. Tasmanian Museum and Art Gallery.
Topics:Karst systems Spider webs Silk Prey capture Gondwana Relict species
Text & map by Mike Gray; photograph by Mike Gray, courtesy of the Australian Museum.
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