Tasmanian Cave Spider
Photo by Paul Flood
Dwelling in the underground world of caves is an astonishing array of fascinating creatures. Tasmania has one of the richest known cave faunas in temperate Australia, including spiders, crickets, beetles, slaters, snails, harvestmen, millipedes, pseudoscorpions and many other invertebrates.
Cave ecosystems directly depend upon the surrounding surface environment. This means it is essential that we maintain the natural soil, vegetation, and water quality around caves. The special nature of karst makes it particularly vulnerable to degradation and such areas should be treated with special care.
Tasmanian cave spider, Hickmania troglodytes
This endemic spider is the largest in Tasmania. A troglophile (animals which spend their entire life cycle underground), it is common in the entrance, twilight and transition zones of caves. It also dwells in suitably dark, sheltered surface habitats such as hollow logs or underneath buildings. Spinning a large horizontal sheet web, around one metre across, the spider’s main prey are cave crickets.
Tasmanian cave spiders are believed to live for many years. Mating involves a prolonged courtship which begins with the male signalling his approach to the female by gently plucking the silk strands of her web. He carefully approaches and taps her with his front legs. This signal seems to deter the female from attacking and eventually the two may join together. On the male’s second pair of legs is a special notch which he uses to restrain the female while he transfers his sperm. During mating, venom may be seen dripping from the fangs of the female, and some males end up becoming a post-nuptial snack!
The female constructs a pear-shaped egg sac suspended from a single thread. She closely guards the eggs for up to nine months (much longer than the usual one to two month period, typical of most other spiders). The silk of the egg sac has properties which make it very resistant to fungal attack. After emergence, the many hundreds of young spiderlings stay close to the parental web for a few weeks before dispersing to other parts of the cave. Few survive to adulthood.
The cave spider belongs to an ancient group believed to be ancestral to modern spiders. This group is characterised by two pairs of book lungs which are visible as brown patches on the underside of the abdomen. Modern spiders have lost one pair of these book lungs. The cave spider’s ancestors date back to before the break-up of the supercontinent Pangaea. Its nearest relatives live in Chile, with other more distant relatives in China and the USA.
These spiders are not aggressive or dangerous to humans, however their webs, constructed near cave entrances, are easily broken by people entering caves.