Australian land hermit crab
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| Australian land hermit crab | ||||||||||||||||||||||
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 A hermit crab from Northern Territory
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| Coenobita variabilis McCulloch, 1909 |
The Australian land hermit crab (Coenobita variabilis) is one of two terrestrial hermit crab species native to Australia and is found in northern parts of Australia including northern Western Australia, Northern Territory and northern Queensland. The other terrestrial species is the strawberry land hermit crab (C. perlatus) which is reportedly restricted to the islands and coral cays of the Great Barrier Reef, north-eastern Australia. The Australian land hermit crab, like all hermit crabs, is a nocturnal, omnivorous crustacean. They thrive in tropical areas near water.
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[edit] Biology
The Australian land hermit crab (Coenobita variabilis) ranges in size between a pea and a tennis ball. They closely resemble the Pacific hermit crab (Coenobita compressus) in appearance and they both have a shortened aquatic development stage. They are light brown to pale brown in color. They have two dark ovals on the front of the head. Their eye stalks are long and are the same color as the body. Each claw has a dark vertical stripe. They have dark brown spots all over the legs. The abdomen is short and fat.
It has been observed that Hermit Crabs live in colonies of more than one hundred [citation needed], disproving their name of 'Hermit' crab. In fact, the Australian hermit crab is a very sociable animal and is very rarely seen alone. Hermit crabs are very well adapted to their environment. Hermit Crabs live most commonly in tropical areas where the humidity is greater than 60%. They also live in areas near water. Due to their gills, Hermit Crabs must always be near or in contact with water. If they are not, they can desiccate and will eventually suffocate. Salt is also necessary for their survival. When land hermit crabs first evolved, they still needed salt in their diet to maintain growth and health.[citation needed] Today, hermit crabs regularly immerse themselves in seawater to clean their bodies and to get their regular intake of salt.
The Australian land hermit crab, like many other hermit crabs, undergoes certain changes during its life. These include moulting and changing shells.
[edit] Shell preference
The preferred seashells of C. variabilis include Babylonia, Nerita, Phasianella, Thais, Tonna and Turban seashells. They are also found to be fond of several varieties of land snail shells such as Aratan snail and rice snail. As hermit crabs grow, they must exchange their shell for a larger one. Since intact gastropod shells are not an unlimited resource, there is frequently strong competition for the available shells, with hermit crabs fighting over shells. The availability of empty shells depends on the abundance of the gastropods and hermit crabs, but most importantly on the frequency of organisms that predate on gastropods but leave the shells intact [2]. A hermit crab with a shell which is too tight cannot grow as fast as hermit crabs with well-fitting shells, and is more likely to be eaten [3]. Although hermit crabs need to change shells regularly, they will not abandon their old shell unless they have a larger and newer one to change into and unless they feel safe.
[edit] Diet
The Australian land hermit crab needs three main elements in their diet to stay healthy; salt, calcium and protein. Many of these elements are obtained naturally in the wild via eating cuttle fish, sand and other (deceased) hermit crabs. Australian hermit crabs are scavengers. In the wild, they eat leaves, fish, bark, grass, fallen fruit, dead animals and even animal excrement.
[edit] Moulting
The Australian land hermit crab grows at a very steady rate. Every 2-18 months, depending on their size, a hermit crab will become very inactive and sluggish. This means that they are preparing for a moult. The signs of moulting are fatigue, eating and drinking large amounts and constantly digging or hiding. An Australian land hermit crab will only moult if it feels safe, has eaten and drunk enough and if it is not disturbed. The moulting process usually begins with the hermit crab sitting on its side and being very inactive. The hermit crab then proceeds to slowly pull off its old exoskeleton and regenerate any lost limbs. After a moult, a hermit crab will be a pinkish colour and look much smaller that it was before. They are very vulnerable at this time and may die if disturbed.
[edit] References
- Harvey A. & R. Brodie (2001). Development of the terrestrial hermit crab, Coenobita compressus, in the laboratory. Journal of Crustacean Biology 21: 715-732.
- Jones, S. & G. J. Morgan (1994). A Field Guide to Crustaceans of Australian Waters. Western Australian Museum. Chatswood, N.S.W. (Australia) : Reed Books. ISBN 0-7301-0403-6.
- ITIS Standard Report Page: Paguroidea
- Species Bank Coenobita variabilis (Family Coenobitidae)
