Form and Function

The Hickmania troglodytes is the largest cave spider in most Tasmanian caves with a body length raging from 13-20Used with permission by Natalie Tapson millimeters and a leg span that can be as large as 180 millimeters. These spiders weave a web that can be up to a meter long. (Australian Museum, 2014, Doran, 1999) There is sexual dimorphism between the males and females in the sense that males have longer legs and they also have a kink-like-curve at the end of one of those legs that they use for mating. (Australian Museum 2014, Tasmanian Parks and Wildlife Service 2014) You can learn more about how this is used for mating in our reproduction section. They have a grayish brown abdomen and two pairs of book lungs which are found on the anterior. These book lungs are used in the respiratory system of the spider for breathing. (Tasmanian Parks and Wildlife Service, 2014, Australian Museum, 2014) Having two pairs of book lungs is actually an ancestral trait because modern spiders only have one pair of book lungs. This means that the Tasmanian Cave Spider belongs to an ancestral group.  The closest relatives of the Hickmania troglodytes are found in South America. (Tasmania Parks and Wildlife Service, 2014)

            This spider has adapted to the dark, damp, humid cave environment by losing its terrestrial adaptations that prevented water loss. Doing this allowed the spider to live and survive in a moist environment without retaining too much water. This makes the spider highly sensitive to change which aids in its role of managing cave life. One of this spiders primary functions in the cave is to let the other cave organisms know when the outside environment is healthy or not healthy, as we learned in the habitat section. The spider’s adaptation to the cave environment that makes it sensitive to change serves as a warning function for the cave fauna and a test to see how healthy the ecosystem of the cave is. (Doran et al, 1999)

The Tasmanian Cave Spider is one of the major predators in Tasmanian caves. It hangs from its legs on its web and waits for other cave organisms to get caught in its web. It then eats the prey which mostly includes various other insects, however its main source of food is cave crickets. (Tasmanian Parks and Wildlife Service, 2014, Australian Meseum, 2014) Cave crickets are also very important to the health of the cave because it provides nutrients for the cave spider and other organisms with feces and itself. This primary food source for the Tasmanian Cave Spider is essential to its life and to the lives of the rest of the cave fauna because without it, the Cave Spiders would be less abundant and would not serve their function of warning the other cave fauna as well. (Doran et al,1999)

The Tasmanian Cave Spider is essential to cave life in many Tasmanian caves. They keep the cave in balance because they are predators and they warn the other cave fauna of pending danger. The Tasmanian cave  spider however is not harmful to people. People often accidentally break their webs because it is in the entrance of the cave, but the spider never shows aggression towards people. (Tasmanian Parks and Wildlife Service, 2014) So, if you are ever exploring a cave in Tasmania, don’t be afraid of this spider and be on the lookout for this guy to get a closer look!

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