Tasmanian Cave Spider

Introduction

The Tasmanian Cave Spider is the last of an old Gondwanan lineage of spiders and its nearest relatives are found in South America.

Identification

The Tasmanian Cave Spider is large, weaving 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. 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.

Distribution

The Tasmanian Cave Spider 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 (Tasmania).

Feeding and diet

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.

Life history cycle

Courtship and mating in the Tasmanian Cave Spider 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 communicating 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 mm 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 eight to ten months, an unusually long time, and disperse within a month. The life- of these spiders is also long, and may prove to last several decades.

Conservation status

The Tasmanian Cave Spider 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.

References

Source: Doran, N.E., Richardson, A.M.M. & Swain, R., 2001, 'The reproductive behaviour of Hickmania troglodytes, the Tasmanian cave spider (Araneae, Austrochilidae)', Journal of Zoology , 253, pgs. 405-418