Coconut crab
Encyclopedia
The coconut crab, Birgus latro, is a species of terrestrial hermit crab
, also known as the robber crab or palm thief. It is the largest land-living arthropod
in the world, and is probably at the upper size limit of terrestrial animals with exoskeleton
s in today's atmosphere at a weight of up to 4.1 kg (9 lb). It is found on islands across the Indian Ocean
and parts of the Pacific Ocean
as far east as the Gambier Islands
, mirroring the distribution of the coconut palm
; it has been extirpated from most areas with a significant human population, including mainland Australia
and Madagascar
.
The coconut crab is the only species
of the genus
Birgus, and is related to the terrestrial hermit crab
s of the genus Coenobita
. It shows a number of adaptation
s to life on land. Like hermit crabs, juvenile coconut crabs use empty gastropod shell
s for protection, but the adults develop a tough exoskeleton on their abdomen and stop carrying a shell. Coconut crabs have evolved organs known as "branchiostegal lungs", which are used instead of the vestigial gill
s for breathing. They cannot swim, and will drown if immersed in water for long. They have developed an acute sense of smell, which has evolved convergently
with that of insect
s, and which they use to find potential food sources. Mating occurs on dry land, but the females migrate to the sea to release their fertilised eggs as they hatch. The larvae are plankton
ic for 3–4 weeks, before settling to the sea floor and entering a gastropod shell. Sexual maturity
is reached after about 5 years, and the total lifespan may be over 60 years.
Adult coconut crabs feed on fruits, nuts, seeds, and the pith
of fallen trees, but will eat carrion and other organic matter opportunistically. The species is popularly associated with the coconut, and has been widely reported to climb trees to pick coconuts, which it then opens to eat the flesh. While coconut crabs can climb trees, and can eventually open a coconut collectively, coconuts are not a significant part of their diet. Coconut crabs are hunted wherever they come into contact with humans, and are subject to legal protection in some areas. In the absence of precise information, the IUCN lists the species as Data Deficient
.
in the world; reports about the size of Birgus latro vary, but most sources give a body length of up to 40 cm (15.7 in), a weight of up to 4.1 kg (9 lb), and a leg span of more than 0.91 m (3 ft), with males generally being larger than females. The carapace
may reach a length of 78 mm (3.1 in), and a width of up to 200 mm (7.9 in).
The body of the coconut crab is, like that of all decapods
, divided into a front section (cephalothorax
), which has 10 legs
, and an abdomen
. The front-most pair of legs has large chelae
(claws), with the left being larger than the right. The next two pairs, as with other hermit crabs, are large, powerful walking legs with pointed tips, which allow coconut crabs to climb vertical or overhanging surfaces. The fourth pair of legs is smaller with tweezer
-like chelae at the end, allowing young coconut crabs to grip the inside of a shell or coconut husk to carry for protection; adults use this pair for walking and climbing. The last pair of legs is very small and is used by females to tend their eggs, and by the males in mating. This last pair of legs is usually held inside the carapace
, in the cavity containing the breathing organs. There is some difference in colour between the animals found on different islands, ranging from orange-red to purplish blue; in most regions, blue is the predominant colour, but in some places, including the Seychelles
, most individuals are red.
Although Birgus latro is a derived type of hermit crab
, only the juveniles use salvaged snail
shells to protect their soft abdomens, and adolescents sometimes use broken coconut shells to protect their abdomens. Unlike other hermit crabs, the adult coconut crabs do not carry shells but instead harden their abdominal terga by depositing chitin
and chalk
. Not being constrained by the physical confines of living in a shell allows this species to grow much larger than other hermit crabs in the family Coenobitidae. Like most true crabs
, B. latro bends its tail underneath its body for protection. The hardened abdomen protects the coconut crab and reduces water loss on land, but has to be moulted periodically. Adults moult annually, and dig a burrow up to 1 m (3.3 ft) long in which to hide while vulnerable. It remains in the burrow for 3 to 16 weeks, depending on the size of the animal. After moulting
, it takes 1 to 3 weeks for the exoskeleton
to harden, depending on the animal's size, during which time the animal's body is soft and vulnerable, and it stays hidden for protection.
e, coconut crabs cannot swim, and they will drown if left in water for more than an hour. They use a special organ called a branchiostegal lung
to breathe. This organ can be interpreted as a developmental stage between gill
s and lung
s, and is one of the most significant adaptations of the coconut crab to its habitat
. The branchiostegal lung contains a tissue
similar to that found in gills, but suited to the absorption of oxygen
from air, rather than water. This organ is expanded laterally and is evaginated to increase the surface area; located in the cephalothorax, it is optimally placed to reduce both the blood/gas diffusion distance and the return distance of oxygenated blood to the pericardium
. Coconut crabs use their hindmost, smallest pair of legs to clean these breathing organs and to moisten them with water. The organs require water to properly function, and the coconut crab provides this by stroking its wet legs over the spongy tissues nearby. Coconut crabs may drink water from small puddles by transferring it from their chelipeds to their maxillipeds.
In addition to the branchiostegal lung, the coconut crab has an additional rudimentary set of gills. Although these gills are comparable in number to aquatic species from the families Paguridae
and the Diogenidae, they are reduced in size and have comparatively less surface area.
molecules in water or hydrophobic
molecules in air. As most crabs live in the water, they have specialised organs called aesthetascs on their antennae
to determine both the concentration and the direction of a smell. However, as coconut crabs live on the land, the aesthetascs on their antennae are shorter and blunter than those of other crabs and look more like those of insect
s. While insects and the coconut crab originate from different evolutionary paths, the same need to detect smells in the air led to the development of remarkably similar organs, making it an example of convergent evolution
. Coconut crabs flick their antennae as insects do to enhance their reception. They have an excellent sense of smell and can detect interesting odours over large distances. The smells of rotting meat, bananas, and coconuts, all potential food sources, catch their attention especially. Research has shown that the olfactory system
in the coconut crab's brain is well-developed compared to other areas of the brain.
s and deposit a mass of spermatophores on the abdomen of the female; the abdomen opens at the base of the third pereiopods, and fertilisation is thought to occur on the external surface of the abdomen as the eggs pass through the spermatophore mass. The extrusion of eggs occurs on land in crevices or burrows near the shore. Shortly thereafter, the female lays her eggs and glues them to the underside of her abdomen, carrying the fertilised eggs underneath her body for a few months. At the time of hatching, the female coconut crab releases the eggs into the ocean. This usually takes place on rocky shores at dusk, especially when this coincides with high tide
. The empty egg cases remain on the female's body after the larvae have been released, and the female eats the egg cases within a few days.
The larvae float in the pelagic zone
of the ocean with other plankton
for three to four weeks, during which a large number of them are eaten by predators. The larvae
pass through three to five zoea stages before moulting into the post-larval glaucothoe stage; this process takes from 25 to 33 days. Upon reaching the glaucothoe stage of development, they settle to the bottom, find and wear a suitably sized gastropod shell, and migrate to the shoreline with other terrestrial hermit crabs. At that time, they sometimes visit dry land. Afterwards, they leave the ocean permanently and lose the ability to breathe in water. As with all hermit crabs, they change their shells as they grow. Young coconut crabs that cannot find a seashell of the right size often use broken coconut pieces. When they outgrow their shells, they develop a hardened abdomen. The coconut crab reaches sexual maturity
around five years after hatching. They reach their maximum size only after 40 to 60 years.
and the central Pacific Ocean
, with a distribution that closely matches that of the coconut palm
. The western limit of the range of B. latro is Zanzibar
, off the coast of Tanzania
, while the tropics of Cancer
and Capricorn
mark the northern and southern limits, respectively, with very few population in the subtropics
, such as the Ryukyu Islands
. There is evidence that the coconut crab once lived on the mainlands of Australia
and Madagascar
and on the island of Mauritius
, but it no longer occurs in any of these places. As they cannot swim as adults, coconut crabs must have colonised the islands as planktonic larvae.
Christmas Island
in the Indian Ocean has the largest and densest population of coconut crabs in the world, although it is outnumbered there by more than 50 times by the Christmas Island red crab
, Gecarcoidea natalis. Other Indian Ocean populations exist on the Seychelles
, including Aldabra
and Cosmoledo
, but the coconut crab is extinct on the central islands. Coconut crabs occur on several of the Andaman
and Nicobar Islands
in the Bay of Bengal
. They occur on most of the islands, and the northern atoll
s, of the Chagos Archipelago
.
In the Pacific, the coconut crab's range became known gradually. Charles Darwin
believed it was only found on "a single coral island north of the Society group
". The coconut crab is far more widespread, though it is not abundant on every Pacific island it inhabits. Large populations exist on the Cook Islands
, especially Pukapuka
, Suwarrow
, Mangaia
, Takutea
, Mauke
, Atiu
, and Palmerston Island
. These are close to the eastern limit of its range, as are the Line Islands
of Kiribati
, where the coconut crab is especially frequent on Teraina
(Washington Island), with its abundant coconut palm forest. The Gambier Islands
marks the species' eastern limit.
s (particularly Ochrosia ackeringae
, Arenga listeri
, Pandanus elatus
, P. christmatensis
), nuts (coconuts Cocos nucifera, Aleurites moluccana) and seeds (Annona reticulata
), and on the pith
of fallen trees. However, as they are omnivore
s, they will consume other organic materials such as tortoise
hatchlings and dead animals. They have been observed to prey upon crabs like Gecarcoidea natalis and Discoplax hirtipes
, as well as scavenge on the carcasses of other coconut crabs. During a tagging experiment, one coconut crab was observed catching and eating a Polynesian Rat
(Rattus exulans). Coconut crabs may be responsible for the disappearance of Amelia Earhart's
remains, consuming them after her death and hoarding her bones in their burrows.
It is a common perception that the coconut crab cuts the coconuts from the tree to eat them on the ground. The coconut crab can take a coconut from the ground and cut it to a husk nut, take it with its claw, climb up a tree 10 m (32.8 ft) high and drop the husk nut, to access the content inside. They often descend from the trees by falling, and can survive a fall of at least 4.5 metres (14.8 ft) unhurt. Coconut crabs cut holes into coconuts with their strong claws and eat the contents, although it can take several days before the coconut is opened.
Thomas Hale Streets
discussed the behaviour in 1877, doubting that the animal would climb trees to get at the nuts. In the 1980s, Holger Rumpff was able to confirm Streets's report, observing and studying how they open coconuts in the wild. The animal has developed a special technique to do so: if the coconut is still covered with husk
, it will use its claws to rip off strips, always starting from the side with the three germination
pores, the group of three small circles found on the outside of the coconut. Once the pores are visible, the coconut crab will bang its pincers on one of them until they break. Afterwards, it will turn around and use the smaller pincers on its other legs to pull out the white flesh of the coconut. Using their strong claws, larger individuals can even break the hard coconut into smaller pieces for easier consumption.
, with most aspects of its life linked to a terrestrial existence; they will drown in sea water in less than a day. Coconut crabs live alone in underground burrows and rock crevices, depending on the local terrain. They dig their own burrows in sand or loose soil. During the day, the animal stays hidden to reduce water loss from heat. The coconut crabs' burrows contain very fine yet strong fibres of the coconut husk which the animal uses as bedding. While resting in its burrow, the coconut crab closes the entrances with one of its claws to create the moist microclimate within the burrow necessary for its breathing organs. In areas with a large coconut crab population, some may come out during the day, perhaps to gain an advantage in the search for food. Other times they will emerge if it is moist or raining, since these conditions allow them to breathe more easily. They live almost exclusively on land, returning to the sea only to release their eggs; on Christmas Island
, for instance, B. latro is abundant 6 kilometres (3.7 mi) from the sea.
s and is considered a delicacy
and an aphrodisiac
, and intensive hunting has threatened the species' survival in some areas. While the coconut crab itself is not innately poisonous, it may become so depending on its diet, and cases of coconut crab poisoning have occurred. For instance, consumption of the sea mango Cerbera manghas
by the coconut crab may make the coconut crab toxic due to the presence of cardiac cardenolide
s.
Should a coconut crab pinch a person, it will cause pain and be unlikely to release its grip. Thomas Hale Streets reports a trick used by Micronesia
ns of the Line Islands
to get a coconut crab to loosen its grip: "It may be interesting to know that in such a dilemma a gentle titillation of the under soft parts of the body with any light material will cause the crab to loosen its hold."
In the Cook Islands
, the coconut crab is known as or , and in the Mariana Islands
it is called ayuyu, and is sometimes associated with because of the traditional belief that ancestral spirits can return in the form of animals such as the coconut crab.
as a vulnerable species
, but a lack of biological data caused its assessment to be amended to Data Deficient
in 1996.
Conservation management strategies have been put in place in some regions, such as minimum legal size limit restrictions in Guam
and Vanuatu
, and a ban on the capture of egg-bearing females in Guam and the Federated States of Micronesia
. In the Northern Mariana Islands
, hunting of non-egg-bearing adults above a carapace length of 30 mm (1.2 in) may take place in September, October and November, and only under licence. There is a bag limit of 5 coconut crabs on any given day, and 15 across the whole season.
around 1688. Based on an account by Georg Eberhard Rumphius
(1705), who had called the animal "", Carl Linnaeus (1767) named the species Cancer latro, from the Latin
, meaning "robber". The genus Birgus was erected in 1816 by William Elford Leach
, containing only Linnaeus' Cancer latro, which was thus renamed Birgus latro. Birgus is classified in the family Coenobitidae
, alongside one other genus, Coenobita
, which contains the terrestrial hermit crabs.
Common name
s for the species include coconut crab, robber crab and palm thief, which mirrors the animal's name in other European languages (e.g. ).
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
, also known as the robber crab or palm thief. It is the largest land-living arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
in the world, and is probably at the upper size limit of terrestrial animals with exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
s in today's atmosphere at a weight of up to 4.1 kg (9 lb). It is found on islands across the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and parts of the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
as far east as the Gambier Islands
Gambier Islands
There was a time when the Gambiers hosted a population of several thousand people and traded with other island groups including the Marquesas, the Society Islands and Pitcairn Islands...
, mirroring the distribution of the coconut palm
Coconut
The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
; it has been extirpated from most areas with a significant human population, including mainland Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
.
The coconut crab is the only species
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Birgus, and is related to the terrestrial hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
s of the genus Coenobita
Coenobita
The genus Coenobita contains the sixteen species of terrestrial hermit crabs. The majority of the species are found in the Indo-Pacific region, with only one species in West Africa, one species occurring along the western Atlantic Ocean, and one species occurring on the Pacific coast of the Americas...
. It shows a number of adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
s to life on land. Like hermit crabs, juvenile coconut crabs use empty gastropod shell
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
s for protection, but the adults develop a tough exoskeleton on their abdomen and stop carrying a shell. Coconut crabs have evolved organs known as "branchiostegal lungs", which are used instead of the vestigial gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s for breathing. They cannot swim, and will drown if immersed in water for long. They have developed an acute sense of smell, which has evolved convergently
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
with that of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, and which they use to find potential food sources. Mating occurs on dry land, but the females migrate to the sea to release their fertilised eggs as they hatch. The larvae are plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic for 3–4 weeks, before settling to the sea floor and entering a gastropod shell. Sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
is reached after about 5 years, and the total lifespan may be over 60 years.
Adult coconut crabs feed on fruits, nuts, seeds, and the pith
Pith
Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In eudicots, pith is located in the center of the stem. In monocots, it extends also into flowering stems and roots...
of fallen trees, but will eat carrion and other organic matter opportunistically. The species is popularly associated with the coconut, and has been widely reported to climb trees to pick coconuts, which it then opens to eat the flesh. While coconut crabs can climb trees, and can eventually open a coconut collectively, coconuts are not a significant part of their diet. Coconut crabs are hunted wherever they come into contact with humans, and are subject to legal protection in some areas. In the absence of precise information, the IUCN lists the species as Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
.
Description
Birgus latro is the largest land-living arthropodArthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
in the world; reports about the size of Birgus latro vary, but most sources give a body length of up to 40 cm (15.7 in), a weight of up to 4.1 kg (9 lb), and a leg span of more than 0.91 m (3 ft), with males generally being larger than females. The carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
may reach a length of 78 mm (3.1 in), and a width of up to 200 mm (7.9 in).
The body of the coconut crab is, like that of all decapods
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
, divided into a front section (cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...
), which has 10 legs
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
, and an abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
. The front-most pair of legs has large chelae
Chela (organ)
A chela is a pincer-like organ terminating certain limbs of some arthropods. The name comes from Greek through New Latin . The plural form is chelae. Legs bearing a chela are called chelipeds. Another name is claw because most chelae are curved and have a sharp point like a claw....
(claws), with the left being larger than the right. The next two pairs, as with other hermit crabs, are large, powerful walking legs with pointed tips, which allow coconut crabs to climb vertical or overhanging surfaces. The fourth pair of legs is smaller with tweezer
Tweezers
Tweezers are tools used for picking up and manipulating objects too small to be easily handled with the human hands. They are probably derived from tongs, pincers, or scissors-like pliers used to grab or hold hot objects since the dawn of recorded history...
-like chelae at the end, allowing young coconut crabs to grip the inside of a shell or coconut husk to carry for protection; adults use this pair for walking and climbing. The last pair of legs is very small and is used by females to tend their eggs, and by the males in mating. This last pair of legs is usually held inside the carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
, in the cavity containing the breathing organs. There is some difference in colour between the animals found on different islands, ranging from orange-red to purplish blue; in most regions, blue is the predominant colour, but in some places, including the Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
, most individuals are red.
Although Birgus latro is a derived type of hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
, only the juveniles use salvaged snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
shells to protect their soft abdomens, and adolescents sometimes use broken coconut shells to protect their abdomens. Unlike other hermit crabs, the adult coconut crabs do not carry shells but instead harden their abdominal terga by depositing chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
and chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
. Not being constrained by the physical confines of living in a shell allows this species to grow much larger than other hermit crabs in the family Coenobitidae. Like most true crabs
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
, B. latro bends its tail underneath its body for protection. The hardened abdomen protects the coconut crab and reduces water loss on land, but has to be moulted periodically. Adults moult annually, and dig a burrow up to 1 m (3.3 ft) long in which to hide while vulnerable. It remains in the burrow for 3 to 16 weeks, depending on the size of the animal. After moulting
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
, it takes 1 to 3 weeks for the exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
to harden, depending on the animal's size, during which time the animal's body is soft and vulnerable, and it stays hidden for protection.
Respiration
Except as larvaLarva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e, coconut crabs cannot swim, and they will drown if left in water for more than an hour. They use a special organ called a branchiostegal lung
Branchiostegal lung
A branchiostegal lung is a respiration organ used by some air-breathing arthropods. It is one of the most significant adaptations of some crabs and hermit crabs such as the coconut crab to their terrestrial habitats....
to breathe. This organ can be interpreted as a developmental stage between gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s and lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s, and is one of the most significant adaptations of the coconut crab to its habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
. The branchiostegal lung contains a tissue
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
similar to that found in gills, but suited to the absorption of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
from air, rather than water. This organ is expanded laterally and is evaginated to increase the surface area; located in the cephalothorax, it is optimally placed to reduce both the blood/gas diffusion distance and the return distance of oxygenated blood to the pericardium
Pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...
. Coconut crabs use their hindmost, smallest pair of legs to clean these breathing organs and to moisten them with water. The organs require water to properly function, and the coconut crab provides this by stroking its wet legs over the spongy tissues nearby. Coconut crabs may drink water from small puddles by transferring it from their chelipeds to their maxillipeds.
In addition to the branchiostegal lung, the coconut crab has an additional rudimentary set of gills. Although these gills are comparable in number to aquatic species from the families Paguridae
Paguridae
Paguridae is a family of hermit crabs of the order Decapoda. It contains 542 species in over 70 genera:*Acanthopagurus de Saint Laurent, 1968*Agaricochirus McLaughlin, 1981*Alainopaguroides McLaughlin, 1997...
and the Diogenidae, they are reduced in size and have comparatively less surface area.
Sense of smell
The coconut crab has a well developed sense of smell, which it uses to locate its food. The process of smelling works very differently depending on whether the smelled molecules are hydrophilicHydrophile
A hydrophile, from the Greek "water" and φιλια "love," is a molecule or other molecular entity that is attracted to, and tends to be dissolved by water. A hydrophilic molecule or portion of a molecule is one that has a tendency to interact with or be dissolved by, water and other polar substances...
molecules in water or hydrophobic
Hydrophobe
In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
molecules in air. As most crabs live in the water, they have specialised organs called aesthetascs on their antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
to determine both the concentration and the direction of a smell. However, as coconut crabs live on the land, the aesthetascs on their antennae are shorter and blunter than those of other crabs and look more like those of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s. While insects and the coconut crab originate from different evolutionary paths, the same need to detect smells in the air led to the development of remarkably similar organs, making it an example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
. Coconut crabs flick their antennae as insects do to enhance their reception. They have an excellent sense of smell and can detect interesting odours over large distances. The smells of rotting meat, bananas, and coconuts, all potential food sources, catch their attention especially. Research has shown that the olfactory system
Olfactory system
The olfactory system is the sensory system used for olfaction, or the sense of smell. Most mammals and reptiles have two distinct parts to their olfactory system: a main olfactory system and an accessory olfactory system. The main olfactory system detects volatile, airborne substances, while the...
in the coconut crab's brain is well-developed compared to other areas of the brain.
Life cycle
Coconut crabs mate frequently and quickly on dry land in the period from May to September, especially between early June and late August. Male coconut crabs have spermatophoreSpermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
s and deposit a mass of spermatophores on the abdomen of the female; the abdomen opens at the base of the third pereiopods, and fertilisation is thought to occur on the external surface of the abdomen as the eggs pass through the spermatophore mass. The extrusion of eggs occurs on land in crevices or burrows near the shore. Shortly thereafter, the female lays her eggs and glues them to the underside of her abdomen, carrying the fertilised eggs underneath her body for a few months. At the time of hatching, the female coconut crab releases the eggs into the ocean. This usually takes place on rocky shores at dusk, especially when this coincides with high tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
. The empty egg cases remain on the female's body after the larvae have been released, and the female eats the egg cases within a few days.
The larvae float in the pelagic zone
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
of the ocean with other plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
for three to four weeks, during which a large number of them are eaten by predators. The larvae
Crustacean larvae
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow...
pass through three to five zoea stages before moulting into the post-larval glaucothoe stage; this process takes from 25 to 33 days. Upon reaching the glaucothoe stage of development, they settle to the bottom, find and wear a suitably sized gastropod shell, and migrate to the shoreline with other terrestrial hermit crabs. At that time, they sometimes visit dry land. Afterwards, they leave the ocean permanently and lose the ability to breathe in water. As with all hermit crabs, they change their shells as they grow. Young coconut crabs that cannot find a seashell of the right size often use broken coconut pieces. When they outgrow their shells, they develop a hardened abdomen. The coconut crab reaches sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
around five years after hatching. They reach their maximum size only after 40 to 60 years.
Distribution
Coconut crabs live in the Indian OceanIndian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and the central Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, with a distribution that closely matches that of the coconut palm
Coconut
The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
. The western limit of the range of B. latro is Zanzibar
Zanzibar
Zanzibar ,Persian: زنگبار, from suffix bār: "coast" and Zangi: "bruin" ; is a semi-autonomous part of Tanzania, in East Africa. It comprises the Zanzibar Archipelago in the Indian Ocean, off the coast of the mainland, and consists of numerous small islands and two large ones: Unguja , and Pemba...
, off the coast of Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
, while the tropics of Cancer
Tropic of Cancer
The Tropic of Cancer, also referred to as the Northern tropic, is the circle of latitude on the Earth that marks the most northerly position at which the Sun may appear directly overhead at its zenith...
and Capricorn
Tropic of Capricorn
The Tropic of Capricorn, or Southern tropic, marks the most southerly latitude on the Earth at which the Sun can be directly overhead. This event occurs at the December solstice, when the southern hemisphere is tilted towards the Sun to its maximum extent.Tropic of Capricorn is one of the five...
mark the northern and southern limits, respectively, with very few population in the subtropics
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
, such as the Ryukyu Islands
Ryukyu Islands
The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...
. There is evidence that the coconut crab once lived on the mainlands of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
and on the island of Mauritius
Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...
, but it no longer occurs in any of these places. As they cannot swim as adults, coconut crabs must have colonised the islands as planktonic larvae.
Christmas Island
Christmas Island
The Territory of Christmas Island is a territory of Australia in the Indian Ocean. It is located northwest of the Western Australian city of Perth, south of the Indonesian capital, Jakarta, and ENE of the Cocos Islands....
in the Indian Ocean has the largest and densest population of coconut crabs in the world, although it is outnumbered there by more than 50 times by the Christmas Island red crab
Christmas Island red crab
The Christmas Island red crab, Gecarcoidea natalis, is a species of land crab that is endemic to Christmas Island and the Cocos Islands in the Indian Ocean...
, Gecarcoidea natalis. Other Indian Ocean populations exist on the Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
, including Aldabra
Aldabra
Aldabra, the world's second largest coral atoll, is in the Aldabra Group of islands in the Indian Ocean that form part of the Seychelles. Uninhabited and extremely isolated, Aldabra is virtually untouched by humans, has distinctive island fauna including the Aldabra Giant Tortoise, and is...
and Cosmoledo
Cosmoledo
Cosmoledo is an atoll of the Aldabra Group and belongs to the Outer Islands of the Seychelles. The atoll is 14.5 km long east-west, and 11.5 km north-south. The total land area is about 5.2 km², while the lagoon measures 145 km² in area . It is located at . The closest island is Astove Island,...
, but the coconut crab is extinct on the central islands. Coconut crabs occur on several of the Andaman
Andaman Islands
The Andaman Islands are a group of Indian Ocean archipelagic islands in the Bay of Bengal between India to the west, and Burma , to the north and east...
and Nicobar Islands
Nicobar Islands
The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean...
in the Bay of Bengal
Bay of Bengal
The Bay of Bengal , the largest bay in the world, forms the northeastern part of the Indian Ocean. It resembles a triangle in shape, and is bordered mostly by the Eastern Coast of India, southern coast of Bangladesh and Sri Lanka to the west and Burma and the Andaman and Nicobar Islands to the...
. They occur on most of the islands, and the northern atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
s, of the Chagos Archipelago
Chagos Archipelago
The Chagos Archipelago , is a group of seven atolls comprising more than 60 individual tropical islands in the Indian Ocean; situated some due south of the Maldives archipelago. This chain of islands are the southernmost archipelago of the Chagos-Laccadive Ridge a long submarine mountain range...
.
In the Pacific, the coconut crab's range became known gradually. Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
believed it was only found on "a single coral island north of the Society group
Society Islands
The Society Islands are a group of islands in the South Pacific Ocean. They are politically part of French Polynesia. The archipelago is generally believed to have been named by Captain James Cook in honor of the Royal Society, the sponsor of the first British scientific survey of the islands;...
". The coconut crab is far more widespread, though it is not abundant on every Pacific island it inhabits. Large populations exist on the Cook Islands
Cook Islands
The Cook Islands is a self-governing parliamentary democracy in the South Pacific Ocean in free association with New Zealand...
, especially Pukapuka
Pukapuka
Pukapuka is a coral atoll in the Cook Islands in the Pacific Ocean, with three small islets threaded on a reef that encloses a beautifully clear lagoon. It is the most remote island of the Cook Islands, situated about 1140 kilometres northwest of Rarotonga. It is a triangular atoll with three...
, Suwarrow
Suwarrow
Suwarrow is a low coral atoll in the Cook Islands in the Pacific Ocean. It is about 1,300 km south of the equator and 930 km NNW of Rarotonga, from which it is administered....
, Mangaia
Mangaia
Mangaia is the most southerly of the Cook Islands and the second largest, after Rarotonga.-Geography:...
, Takutea
Takutea
Takutea, in the Cook Islands, is a small uninhabited island 21 km northwest of Atiu in the southern Cook Islands. Because it is only 1.22 km² in size and has a very dangerous landing at the northwest corner of the reef, it has been designated a wildlife sanctuary, mainly for the red-tailed tropic...
, Mauke
Mauke
Mauke is a raised atoll island, the eastern most of the Cook Islands.-Geography:...
, Atiu
Atiu
Atiu, also known as Enuamanu , is an island lying at 187 km to the northeast of Rarotonga, in the Southern Islands group of the Cook Islands Archipelago.-Geography:...
, and Palmerston Island
Palmerston Island
Palmerston Island is a coral atoll in the Cook Islands in the Pacific Ocean about 500 km northwest of Rarotonga. It was discovered by James Cook on 16 June 1774.-Overview:...
. These are close to the eastern limit of its range, as are the Line Islands
Line Islands
The Line Islands, Teraina Islands or Equatorial Islands, is a chain of eleven atolls and low coral islands in the central Pacific Ocean, south of the Hawaiian Islands, that stretches for 2,350 km in a northwest-southeast direction, making it one of the longest islands chains of the world...
of Kiribati
Kiribati
Kiribati , officially the Republic of Kiribati, is an island nation located in the central tropical Pacific Ocean. The permanent population exceeds just over 100,000 , and is composed of 32 atolls and one raised coral island, dispersed over 3.5 million square kilometres, straddling the...
, where the coconut crab is especially frequent on Teraina
Teraina
Teraina, also known as Washington Island is a coral atoll in the central Pacific Ocean and part of the Northern Line Islands which belongs to Kiribati. Obsolete names of Teraina are Prospect Island and New York Island. The island is located approximately 4.71° North latitude and 160.76° West...
(Washington Island), with its abundant coconut palm forest. The Gambier Islands
Gambier Islands
There was a time when the Gambiers hosted a population of several thousand people and traded with other island groups including the Marquesas, the Society Islands and Pitcairn Islands...
marks the species' eastern limit.
Diet
The diet of coconut crabs consists primarily of fleshy fruitFruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
s (particularly Ochrosia ackeringae
Ochrosia ackeringae
Ochrosia ackeringae is a species of flowering plant in the Apocynaceae family that is found in the Malesian region. The specific epithet honours the collector of one of the syntypes.-Description:...
, Arenga listeri
Arenga listeri
Arenga listeri, the Lister's Palm, is a species of flowering plant in the Arecaceae family. It is named after naturalist Joseph Jackson Lister.It is endemic to Christmas Island and is threatened by habitat loss....
, Pandanus elatus
Pandanus elatus
Pandanus elatus is a dioecious tropical plant in the screwpine genus. It is endemic to Christmas Island, an Australian territory in the north-eastern Indian Ocean. Its specific epithet comes from the Latin elatus , in reference to its growth habit.-Description:Pandanus elatus is an erect tree,...
, P. christmatensis
Pandanus christmatensis
Pandanus christmatensis is a dioecious tropical plant in the screwpine genus. It is endemic to Christmas Island, an Australian territory in the north-eastern Indian Ocean. The specific epithet, "christmatensis", comes from its native locality....
), nuts (coconuts Cocos nucifera, Aleurites moluccana) and seeds (Annona reticulata
Annona reticulata
Annona reticulata is a small deciduous or semi-evergreen tree in the plant family Annonaceae.It is best known for its fruit, called custard-apple, a name it shares with fruits of other species from the same genus: A. cherimola and A. squamosa or sometimes it is called wild-sweetsop,...
), and on the pith
Pith
Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In eudicots, pith is located in the center of the stem. In monocots, it extends also into flowering stems and roots...
of fallen trees. However, as they are omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
s, they will consume other organic materials such as tortoise
Tortoise
Tortoises are a family of land-dwelling reptiles of the order of turtles . Like their marine cousins, the sea turtles, tortoises are shielded from predators by a shell. The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The tortoise...
hatchlings and dead animals. They have been observed to prey upon crabs like Gecarcoidea natalis and Discoplax hirtipes
Discoplax hirtipes
Discoplax hirtipes is a species of terrestrial crab.-Description and behaviour:D. hirtipes can be distinguished from other members of the genus Discoplax by the smooth and distinctly inflated carapace. It is also blue or blue-brown in colour, compared to purple or purple-brown in the remaining...
, as well as scavenge on the carcasses of other coconut crabs. During a tagging experiment, one coconut crab was observed catching and eating a Polynesian Rat
Polynesian Rat
The Polynesian Rat, or Pacific Rat , known to the Māori as kiore, is the third most widespread species of rat in the world behind the Brown Rat and Black Rat. The Polynesian Rat originates in Southeast Asia but, like its cousins, has become well travelled – infiltrating Fiji and most Polynesian...
(Rattus exulans). Coconut crabs may be responsible for the disappearance of Amelia Earhart's
Amelia Earhart
Amelia Mary Earhart was a noted American aviation pioneer and author. Earhart was the first woman to receive the U.S. Distinguished Flying Cross, awarded for becoming the first aviatrix to fly solo across the Atlantic Ocean...
remains, consuming them after her death and hoarding her bones in their burrows.
It is a common perception that the coconut crab cuts the coconuts from the tree to eat them on the ground. The coconut crab can take a coconut from the ground and cut it to a husk nut, take it with its claw, climb up a tree 10 m (32.8 ft) high and drop the husk nut, to access the content inside. They often descend from the trees by falling, and can survive a fall of at least 4.5 metres (14.8 ft) unhurt. Coconut crabs cut holes into coconuts with their strong claws and eat the contents, although it can take several days before the coconut is opened.
Thomas Hale Streets
Thomas Hale Streets
Thomas Hale Streets was an American naturalist. His works include Contributions to the Natural History of the Hawaiian and Fanning Islands and Lower California ....
discussed the behaviour in 1877, doubting that the animal would climb trees to get at the nuts. In the 1980s, Holger Rumpff was able to confirm Streets's report, observing and studying how they open coconuts in the wild. The animal has developed a special technique to do so: if the coconut is still covered with husk
Husk
Husk in botany is the outer shell or coating of a seed. It often refers to the leafy outer covering of an ear of maize as it grows on the plant. Literally, a husk or hull includes the protective outer covering of a seed, fruit or vegetable...
, it will use its claws to rip off strips, always starting from the side with the three germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
pores, the group of three small circles found on the outside of the coconut. Once the pores are visible, the coconut crab will bang its pincers on one of them until they break. Afterwards, it will turn around and use the smaller pincers on its other legs to pull out the white flesh of the coconut. Using their strong claws, larger individuals can even break the hard coconut into smaller pieces for easier consumption.
Habitat
Coconut crabs are considered one of the most terrestrial decapodsDecapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
, with most aspects of its life linked to a terrestrial existence; they will drown in sea water in less than a day. Coconut crabs live alone in underground burrows and rock crevices, depending on the local terrain. They dig their own burrows in sand or loose soil. During the day, the animal stays hidden to reduce water loss from heat. The coconut crabs' burrows contain very fine yet strong fibres of the coconut husk which the animal uses as bedding. While resting in its burrow, the coconut crab closes the entrances with one of its claws to create the moist microclimate within the burrow necessary for its breathing organs. In areas with a large coconut crab population, some may come out during the day, perhaps to gain an advantage in the search for food. Other times they will emerge if it is moist or raining, since these conditions allow them to breathe more easily. They live almost exclusively on land, returning to the sea only to release their eggs; on Christmas Island
Christmas Island
The Territory of Christmas Island is a territory of Australia in the Indian Ocean. It is located northwest of the Western Australian city of Perth, south of the Indonesian capital, Jakarta, and ENE of the Cocos Islands....
, for instance, B. latro is abundant 6 kilometres (3.7 mi) from the sea.
Relationship with humans
Adult coconut crabs have no known predators apart from other coconut crabs and humans. Its large size and the quality of its meat mean that the coconut crab is extensively hunted and is rare on islands with a human population. The coconut crab is eaten by Southeast Asians and Pacific IslanderPacific Islander
Pacific Islander , is a geographic term to describe the indigenous inhabitants of any of the three major sub-regions of Oceania: Polynesia, Melanesia and Micronesia.According to the Encyclopædia Britannica, these three regions, together with their islands consist of:Polynesia:...
s and is considered a delicacy
Gastronomy
Gastronomy is the art or science of food eating. Also, it can be defined as the study of food and culture, with a particular focus on gourmet cuisine...
and an aphrodisiac
Aphrodisiac
An aphrodisiac is a substance that increases sexual desire. The name comes from Aphrodite, the Greek goddess of sexuality and love. Throughout history, many foods, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable...
, and intensive hunting has threatened the species' survival in some areas. While the coconut crab itself is not innately poisonous, it may become so depending on its diet, and cases of coconut crab poisoning have occurred. For instance, consumption of the sea mango Cerbera manghas
Cerbera manghas
Cerbera manghas is a small evergreen coastal tree growing up 12 m tall. The shiny dark-green leaves are alternate, ovoid in shape. The flowers are fragrant, possessing a white tubular 5 lobed corolla about 3 to 5 cm in diameter, with a pink to red throat. They have 5 stamens and the ovary is...
by the coconut crab may make the coconut crab toxic due to the presence of cardiac cardenolide
Cardenolide
Cardenolide is a type of steroid. Many plants contain derivatives, collectively known as cardenolides, including many in the form of cardenolide glycosides...
s.
Should a coconut crab pinch a person, it will cause pain and be unlikely to release its grip. Thomas Hale Streets reports a trick used by Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
ns of the Line Islands
Line Islands
The Line Islands, Teraina Islands or Equatorial Islands, is a chain of eleven atolls and low coral islands in the central Pacific Ocean, south of the Hawaiian Islands, that stretches for 2,350 km in a northwest-southeast direction, making it one of the longest islands chains of the world...
to get a coconut crab to loosen its grip: "It may be interesting to know that in such a dilemma a gentle titillation of the under soft parts of the body with any light material will cause the crab to loosen its hold."
In the Cook Islands
Cook Islands
The Cook Islands is a self-governing parliamentary democracy in the South Pacific Ocean in free association with New Zealand...
, the coconut crab is known as or , and in the Mariana Islands
Mariana Islands
The Mariana Islands are an arc-shaped archipelago made up by the summits of 15 volcanic mountains in the north-western Pacific Ocean between the 12th and 21st parallels north and along the 145th meridian east...
it is called ayuyu, and is sometimes associated with because of the traditional belief that ancestral spirits can return in the form of animals such as the coconut crab.
Conservation
Coconut crab populations in several areas have declined or become extinct due to both habitat loss and human predation. In 1981, it was listed on the IUCN Red ListIUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
as a vulnerable species
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
, but a lack of biological data caused its assessment to be amended to Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
in 1996.
Conservation management strategies have been put in place in some regions, such as minimum legal size limit restrictions in Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
and Vanuatu
Vanuatu
Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...
, and a ban on the capture of egg-bearing females in Guam and the Federated States of Micronesia
Federated States of Micronesia
The Federated States of Micronesia or FSM is an independent, sovereign island nation, made up of four states from west to east: Yap, Chuuk, Pohnpei and Kosrae. It comprises approximately 607 islands with c...
. In the Northern Mariana Islands
Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands , is a commonwealth in political union with the United States, occupying a strategic region of the western Pacific Ocean. It consists of 15 islands about three-quarters of the way from Hawaii to the Philippines...
, hunting of non-egg-bearing adults above a carapace length of 30 mm (1.2 in) may take place in September, October and November, and only under licence. There is a bag limit of 5 coconut crabs on any given day, and 15 across the whole season.
Names
The coconut crab has been known to western scientists since the voyages of William DampierWilliam Dampier
William Dampier was an English buccaneer, sea captain, author and scientific observer...
around 1688. Based on an account by Georg Eberhard Rumphius
Georg Eberhard Rumphius
Georg Eberhard Rumphius or originally Rumpf was a German-born botanist employed by the Dutch East India Company in what is now eastern Indonesia, and is best known for his work, Herbarium Amboinense....
(1705), who had called the animal "", Carl Linnaeus (1767) named the species Cancer latro, from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, meaning "robber". The genus Birgus was erected in 1816 by William Elford Leach
William Elford Leach
William Elford Leach FRS was an English zoologist and marine biologist.Leach was born at Hoe Gate, Plymouth, the son of a solicitor. At the age of twelve he went to school in Exeter, studying anatomy and chemistry. By this time he was already collecting marine samples from Plymouth Sound and along...
, containing only Linnaeus' Cancer latro, which was thus renamed Birgus latro. Birgus is classified in the family Coenobitidae
Coenobitidae
Coenobitidae are a family of hermit crabs, widely known for their terrestrial habits. There are 17 species in two genera:*Coenobita Latreille, 1829*Coenobita brevimanus Dana, 1852*Coenobita carnescens Dana, 1851...
, alongside one other genus, Coenobita
Coenobita
The genus Coenobita contains the sixteen species of terrestrial hermit crabs. The majority of the species are found in the Indo-Pacific region, with only one species in West Africa, one species occurring along the western Atlantic Ocean, and one species occurring on the Pacific coast of the Americas...
, which contains the terrestrial hermit crabs.
Common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s for the species include coconut crab, robber crab and palm thief, which mirrors the animal's name in other European languages (e.g. ).