Crab of coconut

The crab of coconut ( Birgus latro ) is largest terrestrial Arthropode of the world. Of the family of the crabs hermits, it is known for its capacity to break Coconut thanks to its strong grips and has to eat the contents of it.

Vernacular names

The crab of coconut is also called crab robber because, according to rumors, inside even of the houses or tents, this animal could fly of the brilliant or metal objects.

The crab of coconut has several other local names. For example, with Guam, in Chamorro, one calls it ayuyu .

Description

Morphology

The specimens of this species reach a weight going generally up to 4 kilos, a length of body generally going up to 400 millimetres and generally up to 1 meter of scale from one leg to another. The male is generally taller than the female (sexual Dimorphisme). Some authors affirm to have found specimens of more than 17 kilograms. This is generally accepted as being the theoretical limit for a terrestrial Arthropode. However, for the aquatic animals whose body is supported by water, the maximum size of an arthropod can be higher (for example the large Japanese crab Macrocheira kaempferi ).

The body of crab of coconut, like that of all the Décapodes, is divided into a frontal section (Céphalothorax) and a Abdomen provided with ten legs. The pair former is provided with enormous grips which it uses to break the coconuts or to raise objects (being able to weigh up to 29 kilograms. The pair of posterior legs is tiny. These legs are usually maintained inside the carapace, in the cavity which shelters the respiratory bodies.

Specificities of the carapace

Although the Birgus latro belongs to the superfamille of the Paguroidea , only the youthful ones recover the shells gastropodes to protect their soft abdomens. Sometimes, they use even the shells of broken coconuts. Contrary to good of other species of Paguroidea , the adult of crab of coconut does not transport artificial protection, but naturally hardens his abdomen while adding to it of the layers of Chitine. They also recroquevillent their tail under their body so as to be protected as do it the majority of truths Crabe S ( Brachyura ). The hardened abdomen protects crab and reduces the water loss during which the body of the animal is soft and vulnerable. There thus remains hidden during this period.

Respiratory system

The crab of coconut cannot swim and would drown in water at the end of a few hours in spite of a system of Branchie S rudimentary, probably a remainder left with the species during its evolution. It uses a special body, named Poumon branchiostégal, to breathe. This body can be interpreted like pertaining at an intermediate stage between the gill and the Poumon and is one of the most significant adaptations of crab of coconut to its habitat. The rooms of this respiratory body are located in the upper part of the Céphalothorax, and contain a fabric similar to that found in the gills, but adapted to absorb the Oxygène rather air than of water. Such a body needs water to function. The crab provides for this by humidifying its lung with its pair with posterior legs all while cleaning them. The sense of smell functions differently according to whether the humées molecules are absorbent molecules in water or of the hydrophobic molecules in the air. Since the majority of crabs live in the Eau, they have special bodies named Aesthetasc S on their antennas which determine the source and the concentration of the odors in water. However, since that the crab of coconut lives on ground, the aesthetascs their antennas are significantly different from those of other crabs and resemble of advantage the olfactive bodies of the named Insecte S Sensille S.

Distribution

Habitat

The crabs of coconut usually live in underground dens or rock slits, according to the local ground, but mainly, they dig their own dens in sand or a soft ground. During the day, the animal remains hidden, either to protect itself from predatory, or to decrease the water loss due to heat. While it rests in its den, the crab of coconut uses one of its grips to close the exit of it to create the wet environment necessary to its respiratory bodies. In the zones of large crab population of coconut, some can also leave during the day, to perhaps obtain an advantage in the search for food. If the environment is wet, or if it rains, the crabs of coconut leave sometimes during the day since these conditions their make it possible to breathe more easily.

The adult crabs of coconut live mainly inside the grounds (with 6 kilometers of the sea approximately.

Geographical distribution

The crabs of coconut live in a zone scattered in the Indian Ocean and the Pacific Ocean Western. The largest population and best preserved is on the Christmas island in the Indian Ocean. Vast populations exist with the islands Cook, especially Pukapuka, Suwarrow, Mangaia, Takutea, Mauke, Atiu and the island of Palmerston. Other populations exist on the Seychelles, especially with Aldabra, on the Glorious Îles, with Astove, on the island of the Assumption, and with Cosmoledo, but the crab of coconut is extinct on the principal islands. One also finds them on several of the islands Andaman and Nicobar, in the Bay of Bengal. There are variations of colors between the specimens of various islands which go from purple to dark chestnut while passing by the intense crimson.

Since the adults cannot swim, the crabs of coconut, must have colonized the islands at the time of their state of larvae, which can swim. However, because of the long distances between the islands, certain researchers estimate that a larval state hardly 28 days is not sufficient to cover such a distance, and suppose that the young crabs joined the islands on trees or other objects with the drift.

The distribution contains some hole, for example the neighborhoods of Borneo, in Indonesia, and New Guinea. These islands, which have an environment adapted, and which can be joined easily, do not have a colony of this type of crab because the populations of formerly were driven out until the extinction. However, the crabs of coconut find themselves on the island of Wakatobi and Sulawesi.

Statute of conservation

According to the criteria of UICN, there are not enough data to say if the crab of coconut is a threatened species. Consequently have allots statute DD to him (in English, dated defective , i.e., given insufficient). However, according to certain reports/ratios the populations are sufficiently numerous, of which largest on the island of the Millenium. It is believed that the crabs of coconut are sufficiently numerous on certain islands, but rather rare on others. The coastal developments on several islands reduce the natural habitat of this shellfish.

The young crabs of coconut are vulnerable to the carnivores introduced like the rats, the pigs and the ants (such Anoplolepis gracilipes). However the adult crabs do not have the predatory natural ones and are eaten only by the human ones. The adults have a weak sight and locate the danger by the vibrations of the ground.

In general, it seems that the many human populations is a negative effect on the crab populations of coconut and, in certain areas, one reports that the populations are in reduction because of excessive huntings. The crab of coconut is protected in certain zones from safeguarding, with prohibition of hunting during the period of the loves, and the obligation not to drive out the specimens of size lower than a fixed limit.

Relations with the human being

The crab of coconut is appreciated for its flesh by the autochtones Pacifique

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