The Caribbean hermit crab (Coenobita clypeatus), also known as the tree crab, the tree-climbing crab, the soldier crab, and the purple pincher, is a species of land hermit crab which lives in the Caribbean Sea, southern Florida, Venezuela, and the Bermuda Islands.
This species is commonly sold in the United States as a pet. The last of its common names is due to the distinctive purple claw. In captivity they can live to be over 30 years old (and over 40 years in exceptional cases).
Caribbean hermit crabs are omnivorous scavengers who live in colonies of 100 or more in inland areas, and who like to hide in caves or the roots of a tree. They prefer a relative humidity level between 70% and 78%, and a temperature of 24°C (75°F).
Coenobita clypeatus is a member of the phylum Arthropoda and the class Malacostraca. The color varies from a pale red to a dark brown or burgundy.
The eyestalks are round and white, with a black or brown stripe on the bottom. The eyes are oval in shape. The abdomen is short and fat. There are four walking legs, four tiny legs to hold the shell in place, a small pincher, a large purple pincher, and four antennae.
Although these hermit crabs live on land, they have gills, rather than lungs. The high relative humidity of their native environments, plus water carried in the shell, allows their modified gills to remain wet and thus to function properly in extracting oxygen from the air.
Caribbean hermit crabs are both herbivorous and scavengers. In the wild, land hermit crabs
feed off of coconut
trees, left overs from humans, and dead organisms, such as fish and other crabs. Hermit crabs are able to bury their food in the sand to consume later, but other crabs may find them and consume it themselves. In captivity, land hermit crabs can be fed commercial foods that come in many varieties. Hermit crabs may also eat treats that include vegetables such as coconuts
, or spinach
Shell usage and shell fights
The land hermit crab
uses a shell
to protect its delicate body. The shell is sometimes that of a land snail
when it is young, but is usually that of a marine snail. When a marine snail dies, the soft parts decompose or are eaten and the empty shell often washes up onto the shore. The hermit crab can then find and occupy the shell. Larger shells are necessary as the crab grows, but that growth is quite slow.
Hermit crabs are very particular about their shells. Shell switching is not uncommon as the crab searches for the perfect shell. A desired characteristic of a shell is an opening about the size of the large claw, plus about 2½–3 mm (1/10 in to 1/8 in) all around (more for larger crabs). When threatened, the crab withdraws into the shell and blocks the entrance with the large claw.
Fierce shell fights can occur when the shell supply is not adequate. The loser often dies since many hermit crabs will not release their grip on their shell until they are torn apart. The loss of limbs in shell fights is common, but may not result in death especially since the hermit crab can choose to drop (autotomize) a limb to disengage from the conflict.
Shells used by Coenobita clypeatus
When choice of shells is available, C. clypeatus
seems to prefer intact undamaged shells with circular
openings and a smooth mother-of-pearl
interior. However in a pinch, they will use whatever they can find that they can fit into, even discarded, man-made items such as plastic glasses, broken bottles or tiny one-person jam jars.
Some of the snail (class Gastropoda, phylum Mollusca) shells with circular/oval openings available for their use in the wild include :
- *turban shells (genus Turbo, family Turbinidae) - Examples:
- *Filose Turban (Turbo cailletii) - Region: Western Atlantic Ocean - ZipCodeZoo entry - Picture - Picture
- *Channeled Turban (Turbo canaliculatus) - Region: Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *Chestnut or Knobby Turban (Turbo castanea) - Region: Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *West Indian Topshell shells (Cittarium pica, family Trochidae - was Turbo pica) - also called the Magpie, the West Indian Topsnail, or erroneously the West Indian Whelk. Over fishing of this snail (Bermuda) has been known to negatively effect the Caribbean hermit crab population. - Region: Indonesia, Bermuda - ZipCodeZoo entry - Picture
- *periwinkle shells (genera Littorina, Littoraria, or Echinolittorina/Nodilittorina ; family Littorinidae) - Examples:
- *White-Spotted Periwinkle (Echinolittorina/Nodilittorina meleagris) - Region: N.America, Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *Dwarf Brown Periwinkle (Echinolittorina/Nodilittorina mespillum) - Region: N.America, Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *Mangrove Periwinkle (Littoraria angulifera) - Region: North America, Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *Common Periwinkle (Littorina littorea) - Region: North America, Caribbean, Europe, India, etc. - ZipCodeZoo entry - Picture
- *"tulip shell" shells (genus Fasciolaria, family Fasciolariidae) - Examples:
- *Yellow Tulip Shell (Fasciolaria bullisi) - Region: Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *Hunter's Tulip Shell (Fasciolaria lilium hunteria) - Region: Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *Banded Tulip Shell (Fasciolaria lilium tortugana) - Region: the Americas - ZipCodeZoo entry - Picture
- *True Tulip Shell (Fasciolaria tulipa) - Regions: Americas, India, etc. - ZipCodeZoo entry - Picture
- *nutmeg shells (genus Trigonostoma ; family Cancellariidae) - Example:
- *Rugosa Nutmeg (Trigonostoma rugosum) - Region: Florida, E.Pacific, Western Atlantic - ZipCodeZoo entry - Picture
- *tun shells (genus Tonna, family Tonnidae) - Examples:
- *Atlantic Spotted Tun (Tonna maculosa) - Region: the Americas, Africa - ZipCodeZoo entry - Picture
- *Atlantic Partridge Tun (Tonna pennata) - Region: the Americas, Western Atlantic Ocean - ZipCodeZoo entry - Picture
- *King's Crown Conch shells (Melongena corona, family Melongenidae) - Region: Western Atlantic Ocean - ZipCodeZoo entry - Picture
- Superorder under revision - Order Pulmonata - have developed lungs, rather than gills
- *Haitian Tree Snail shells [also called "Candy Striped" or "Rainbow" shells] (Liguus virgineus, family Orthalicidae) - Region: Cuba - ZipCodeZoo entry - Picture
Growth and molting
The Caribbean hermit crab, like all species of hermit crabs, grows through a strenuous and hazardous process called molting where the exoskeleton of the animal is shed and a new, soft exoskeleton is exposed from beneath. A molt also allows the crab to regrow lost appendages. The smallest Caribbean hermit crabs will molt many times per year, while the largest (about the size of a baseball) may only molt once every 18 months.
Before a molt, the hermit crab will attempt to eat enough to survive the molting period. It will obtain sea salt from salt water to aid in shedding the old exoskeleton and will store a supply of water. The crab may even seek out a smaller, tighter shell for easier digging or a larger shell for room to shed. Normally the molt is started by digging down into the moist substrate (with its shell) and creating a little cave. There total darkness triggers the secretion of the molting hormone ecdysone.
Over a period of up to three months (larger crabs require the most time),
- the buried, molting crab sheds the old exoskeleton in a process called ecdysis,
- lost appendages may be regrown (completely or partially),
- the new exoskeleton hardens,
- the old exoskeleton is eaten, in order to reuse the calcium and other nutrients,
- the crab regains its strength and returns to the surface.
Sometimes the land hermit crab will molt on the surface where other crabs may eat the shed exoskeleton or even kill the defenseless, molting crab. Circumstances that may cause a surface molt include illness, or the lack of a substrate in which the crab can bury itself.
Land hermit crab reproduction
Female land hermit crabs release fertilized eggs into the ocean where the salt water causes them to hatch. The hatchlings live in the ocean until their gills
mature enough to be able to extract oxygen
Once on land, the hermit crab begins to drink fresh water, but still requires salt water (sea salt) for functions like molting. After the last developmental molt, the modified gills lose the ability to process water and the crab can drown if trapped under water.
Captive C. clypeatus will not breed in an indoor environment, but have done so in an outdoor enclosure. None of the young lived past 10 days.
- Nieves-Rivera, Á. M. & E. H. Williams, Jr. (2003). "Coenobita clypeatus (Herbst) of Mona Island crustaceans". Crustaceana 76 547–558.
- Greenaway, P. (2003). "Terrestrial adaptations in the Anomura (Crustacea: Decapoda). In: Lemaitre, R., and Tudge, C.C. (eds) "Biology of the Anomura". Proceedings of a symposium at the Fifth International Crustacean Congress, Melbourne, Australia, 9-13 July 2001". Memoirs of Museum Victoria 60 (1): 13–26.
- Marine resources and fisheries strategic and comprehensive conservation plan – 2005, Appendix 1B: marine species overview, invertebrate species