The Largest Crab In The World

The Largest Crab In The World

Birgus Latro

1. The coconut or robber crab (Birgus latro) has a wide distribution ranging from Eastern Africa, through the Indian Ocean islands to the Pacific Ocean islands. 

2. The one which is nicknamed the “robber crab” is an extraordinary creature, with red eyes, and able to change its body colour from violet blue to an orangey red according to its habitat. Weighing up to 4 kg and 40 cm in length, with a leg span of up to one metre, this is the biggest land crab in the world!

3. The coconut or robber crab, Birgus latro, obtained its name from a reputation for stealing nuts from coconut trees (hence the specific name latro which is Latin for "robber"). 

4. The coconut crab (Birgus latro), from the family of hermit crabs, is known for its  ability to open coconuts by crushing them , with its strong claws, in order to eat the coconut flesh. 

5. Its abdomen is equipped with ten legs. The front pair has very large claws which it uses to break coconuts. The next two pairs are used for moving. The extremities of the third pair are divided into two: thanks to this anatomical peculiarity it is able to climb trees to eat their fruit. The rear legs, which are tiny, are usually kept under the shell.

6. Like all hermit crabs, the coconut crab sheds its outer skin as it grows, and it may also use pieces of coconut to protect its body while it is soft. At this stage, it is an ocean crab. 

7. But after the age of three years, it leaves the ocean. Its shell hardens and it loses its ability to breathe in the water. The coconut crab is then no longer suited to swimming and would drown despite its rudimentary system of gills, probably a vestige of its evolution. It uses a specific organ for breathing, which is halfway between gills and a lung, adapted to take oxygen from the air rather than from water.

8. Another unusual thing about the coconut crab is its powerful sense of smell. The coconut crab has antennae which resemble the organs of smell which insects have. The crab moves them by twitching to improve its perception of smell. It can therefore make out interesting smells over great distances, especially those emanating from sources of food: banana, coconut, pandanus fruit or decomposing  meat.

9. The coconut crab normally lives in a den or a rock crevice, or digs a burrow in the sand or in loose soil. It generally lives in forested and sandy areas where there are coconut trees.

10. Being quite timid, it moves around quietly making clicking noises, but can become very lively when it is on the alert. The coconut crab, with its poor eyesight, is relatively easy prey for man, who is its main, if not its only, predator.

11. Coconut crabs are a type of hermit crab; however they abandon the necessity of residing in a discarded snail shell at a small size and go through life with no added protection other than their own carapace. 

12. They are the largest land dwelling invertebrate in the world and can reach a weight in excess of 5kg. 

13. Coconut crabs breed on land but the female releases the eggs in the ocean where they immediately hatch. The oceanic larval stage lasts 2-3 weeks. Once on land the growth rate is slow and it is estimated to take 8-10 years to reach the size limit of 3 inches (76mm) across the back.

14. The coconut crab, Birgus latro, is a crustacean related to hermit crabs.

15. The juveniles live in sea-snail (gastropod) shells but the adults live without shells and grow to large sizes on land. 

16. The coconut crab is one the largest of all crabs and reaches weights of over 4 kg (with some reports of weights up to 14 kg). The adults have massive crushing claws and long legs which enable them to climb trees. 

17. The colour of adults varies from light violet through to deep purple to brown. 

18. The coconut crab is distributed in tropical islands from the Indian Ocean to French Polynesia in the Pacific Ocean. Its vulnerability to animals such as dogs and pigs as well as the destruction of its coastal habitats have probably accounted for its disappearance in many islands and atolls.

19. Adult coconut crabs live alone in underground burrows and rock crevices in coastal forest regions and some have been found up to 6 km from the sea. 

20. Adults cannot swim and will drown in seawater.

21. Coconut crabs generally remain hidden during the day and come out to look for food at night. They eat other crabs, dead animals, and will sometimes raid rubbish bins for human food scraps. They eat rotting leaves as well as  Pandanus fruit and coconuts that have fallen to the ground. 

22. They are capable of removing the husk of a coconut with their large claws and piercing its soft germination eye with one of their legs.

23. Coconut crabs have separate sexes. 

24. During mating, the male transfers sperm packets (spermatophores) to the underside of a soft-shelled female. A few weeks later, the female releases her eggs. These are fertilised as they pass over the spermatophores and form a spongy, orange, egg mass, which is carried underneath her body for a few months. 

25. The female moves to the shore-line and releases the fertilised eggs into the ocean at high tide. These hatch into small forms (the larval stages) which drift in the ocean for about a month. Less than one in every thousand survives to settle on shore and enter a suitable sea-snail shell. 

26. As they change into juveniles, they lose the need for protective shells and move further inland as they grow. Less than one in every hundred survives to become an adult.

27. As in all crustaceans, coconut crabs cast of their hard covering at intervals in order to grow. When the old shell is cast of , it takes about 30 days for a new shell to harden and, as the crab is vulnerable during this time, it stays hidden for protection. Coconut crabs are capable of reproducing at approximately 5 years of age and can live for over 30 years.