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Animals adapted to cave environments, living in the 'dark zone' of deep cave regions, are called troglodytes. 

Tartarus nurinensis
Common name: A blind cave spider, A Mullamullang Cave Spider, in its distinctive lampshade-shaped web. Image: Norman Poulter
© Norman Poulter

These include detrivores, such as beetles and cockroaches and carnivores, such as spiders.

The energy for their survival comes from washed in or deposited organic detritus as well as penetrating plant root mats. The detritus comes from the cave entrances, which are frequented by species living on the surface outside the caves.

One of the most spectacular spider troglodytes is the Mullamullang Cave Spider, Tartarus mullumullangensis, from the Nullarbor Plain caves. This palm-sized, long legged, creamy-white spider has no pigmentation or eyes. It spins a large, cylindrical lampshade-shaped web, with one end attached to the cave wall and the other, open end guyed out to surrounding rocks. It sits there and waits for its prey to blunder in.

The Mullamullang Cave Spiders are closely related to spiders found in the forests of southwest and southeast Australia. This suggests that the Nullarbor Plain was probably once a wetter, more vegetated region. Gradual climatic drying would have concentrated vulnerable species in moister refuge areas, like cave entrances and deep fissures in the limestone rock. Some of these spider populations, including the ancestors of the Mullamullang Cave Spider, became adapted to the deep cave environment, losing unnecessary features like pigment and eyes and reducing energy requirements.

Four species of Tartarus spiders have been described from separate Nullarbor cave systems by Australian Museum scientist Mike Gray. Recently, new populations of these spiders have been found with up to 80 spiders in a single chamber. Unfortunately, the remoteness of their cave habitats makes long-term studies difficult, and there is much still to be learned.