Coconut Crab (The World’s Largest Land Crab)

The coconut crab (Birgus latro) also called the robber crab or palm thief, large nocturnal land crab of the Indian Ocean, the Indo-Pacific region, and the southern Pacific Ocean, with a distribution that closely matches that of the coconut palm.

Adult coconut crabs are about 1 meter from leg tip to leg tip and weigh about 4.5 kg Depending on where they live, coconut crabs can be deep blue, red, or purple-red in color, or any combination of the three. Their left claw is slightly larger than their right, both of which are located near the front of their bodies. Their pinchers are among the strongest of all land animals. They have two pairs of walking legs that have pointed dactyls at the end used for gripping tree bark and other tough surfaces. Interestingly, coconut crabs have gills but, as a result of evolution and thousands of years on land, they don’t work, they instead use lungs for gas exchange as humans do.

Coconut crabs live alone in 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. They live almost exclusively on land, returning to the sea only to release their eggs.

Coconut crabs are also known as robber crabs because might be tied to that incredible sense of smell. Unlike most other crabs, they have specially shortened antennae to detect smells in the air over great distances. Coconut crabs ignore objects that have been washed clean of scents, suggesting that they may only abscond with things that carry a faint whiff of food. The smells of rotting meat, bananas, and coconuts, all potential food sources, catch their attention especially.

Adult coconut crabs are omnivorous scavengers, which means they eat pretty much anything they can find. They eat animal carcasses, the molted skeletons of other crustaceans, tropical fruits, and coconut meat. They often use their claws to poke a hole into the soft eye of coconut before splitting it open, but some coconut crabs will drag coconuts to the top of a tree, dropping them to break them open. They will bring larger food items back to their home burrows for safe consumption and storage for later. They eat more ahead of molting periods and will eat their own exoskeletons after shedding.

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 high and drop the husked nut, to access the coconut flesh inside. They often descend from the trees by falling and can survive a fall of at least 4.5 m unhurt. Coconut crabs cut holes into coconuts with their strong claws and eat the contents. If the coconut is still covered with husk, it will use its claws to rip off strips. Once the pores are visible, the coconut crab bangs its pincers on one of them until it breaks.

Coconut crabs mate frequently and quickly on dry land. The female lays her eggs shortly after mating and glues them to the underside of her abdomen, carrying the fertilized eggs underneath her body for a few months. At the time of hatching, the female coconut crab migrates to the seashore and releases the larvae into the ocean. This usually takes place on rocky shores at dusk, especially when this coincides with high tide.

The larvae float in the pelagic zone of the ocean with other plankton for 3–4 weeks, during which a large number of them are eaten by predators. 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. Afterward, they leave the ocean permanently and lose the ability to breathe in water. Coconut crabs are related to hermit crabs, and they act like it when they’re young. Because its shell is thin and soft when it is small, a juvenile coconut crab wears an empty seashell or coconut husk on its back. As the crab grows, its shell becomes thicker and harder. The coconut crab reaches sexual maturity around 5 years after hatching. They reach their maximum size only after 40–60 years.

Adult coconut crabs have no known predators apart from other coconut crabs and humans. Its large size and the quality of its meat means that the coconut crab is extensively hunted and is very rare on islands with a human population. Other dangers to coconut crabs relate to climate change, which may affect food availability and reproductive cycles, and ocean acidification, which would make life difficult for larval and juvenile crabs to grow their exoskeletons.

Coconut crab populations in several areas have declined or become locally extinct due to both habitat loss and human predation. In 1981, it was listed on the IUCN Red List as a vulnerable species, but a lack of biological data caused its assessment to be amended to "data deficient" in 1996. In 2018, IUCN updated its assessment to "vulnerable".

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