The Coconut Crab: The Horrifying Behemoth Of Tropical Islands

The coconut crab, Birgus latro, is also called robber crab. This is a sizeable nocturnal land crab of the southwest Pacific and Indian oceans. It looks similar to hermit crabs and king crabs as they are closely related.

This colossal crustacean is gaining notice due to the recent pictures that surfaced of a coconut crab climbing into trash cans and even eating birds. This crab is so giant that you would indeed be frightened if you found it rummaging through your trash.

This crab and similar species are all decapod crustaceans. Adult coconut crabs are about 1 meter (40 inches) from leg tip to leg tip and weigh about 4.5 kg (10 pounds). Consider that for size! Fully grown adult coconut crab ranges in coloring from light violet to brown and deep purple, while young adults are brown, with black stripes on their legs.

The Coconut Crab: The Horrifying Behemoth Of Tropical Islands

These incredible crustaceans are generalist scavengers that feed on fallen fruit, carrion, and the shells of other crabs. They can be seen trying to get into a trash can, primarily looking for food if they lack calcium.

The coconut crab is known for its ability to use its massive pincers to crack open coconuts. The largest ones can exert a force of 3,300 newtons with their pincers. That is one tough grip! Besides that, this crab also knows how to open coconuts by dropping them from trees or by striking them repeatedly with their pincers. They can even use their pincers to pierce the coconut's husk before splitting the seed open.

A lot of naturalists believe that these large crabs were first described by the legendary biologist Charles Darwin. He wrote about a coconut crab after encountering it during his Beagle voyage through the Indian Ocean. In his writings, coconut crabs are described as monstrous in size. He marveled at the ease in which the coconut crab cracked into a hard-shelled coconut covered with husk.

Where Can You Find A Coconut Crab?

The Coconut Crab: The Horrifying Behemoth Of Tropical Islands

This land crab is the world's largest crab. It feeds on everything from coconuts to small mammals and birds. However, they mostly eat coconuts, thankfully, and are aptly named. Better than being called a bird-eating crab!

You can find coconut crabs on remote coral atolls and tropical islands throughout the Indo-Pacific. A coconut crab will begin life as microscopic larvae in the ocean. After a month at sea, it will then transition to an entirely terrestrial existence. After growing up, it cannot remain submerged underwater without drowning.

During their growing up, they occupy empty snail shells, like their cousins – hermit. One difference is that a coconut crab re-calcifies its abdomen as it grows. This makes them eventually cease using shells. Over time there are no shells large enough to accommodate them.

After this, adults carve out expansive underground lairs. These caves are often located beneath the roots of coconut trees. They are lined extensively with the husk of coconuts and provide a controlled environment. Coconut crabs occupy their burrows during the heat of the day. They are vigilantly defended against intruders.

Their color varies depending on where they live. In the tropical islands of the Indo-Pacific, juvenile coconut crabs have gills. However, as a result of evolution and thousands of years on land, they don't work. This is why adult crabs can drown in water. A coconut crab will instead use its lungs for gas exchange as humans do.

Coconut Crab Size And Eating Habits

Coconut Crab: The Horrifying Behemoth Of Tropical Islands

Found in Madagascar, Seychelles, and Easter Island, these crabs thrive in tropical lands. They live in burrows which offer them protection and allow them to store food safely. Recently it was discovered that they bury themselves completely during molting periods. At this time, they shed their exoskeleton and grow a larger one to take its place.

Adult crabs are omnivorous scavengers. This means that they do not pick and choose their food. A coconut crab will eat pretty much anything it can find. Ranging from animal carcasses, molted skeletons of other crustaceans, tropical fruits, and coconut meat, these crabs will devour anything.

Coconut crabs can grow to be three feet across, nearly one-and-a-half feet long. Adult species can weigh as much as nine pounds, making it the largest species of land crab on earth. Their males are generally larger than their female counterparts, although not by much.

Coconut Crab: The Horrifying Behemoth Of Tropical Islands

The only part of a coconut crab's body that is not covered by armor is the abdomen. It is covered by thick, leathery skin that has tufts of small bristles.

Female coconut crabs have three large feathery appendages on their abdomens, which they use to carry egg masses.

Coconut crabs use their claws to poke a hole into the soft eye of coconut before splitting it open. However, sometimes they will drag coconuts to the top of a tree and then drop them to break them open. Larger food items will be brought back to their lair for safe consumption and storage for later. Since they eat more ahead of molting periods, they will sometimes eat their own exoskeletons after shedding to compensate for the lack of calcium.

Since they are so large, coconut crabs don't have natural predators. The only known predator this crab has to worry about is humans. Still, their juveniles may be prey for lizards, toads, and feral pigs.

Coconut Crab Population

Coconut Crab: The Horrifying Behemoth Of Tropical Islands

These monstrous crabs start their lives relatively small - as planktonic larvae in the ocean. They feed on other plankton and transform through several life cycles before reaching their juvenile stage and making their way toward land.

As they arrive at the shore, the crabs look for a place to make their burrow. On the way there or shortly after arriving, a young coconut crab will find the perfect shell to call home until it outgrows it. This shell will offer it protection from any potential predators and the elements. After this, they will make their way to building a burrow.

Since coconut crabs are generally nocturnal animals and live alone, they only venture out of their burrows to find food or mate. On larger tropical islands, coconut crabs are often nomadic and will frequently dig new holes for themselves. When they are vulnerable, coconut crabs will stay buried for as long as 16 weeks during molting periods!

As they are solitary animals, they don't have a great need for communication. In the cases when they do encounter other crabs, a coconut crab will use visual cues. These cues are vertical movements of their claws or legs used for signaling to other crabs.

Their mating habits are related to lunar or tidal cycles. A female crab can breed once per summer, with a gestation period of four to six weeks. Both males and females reach sexual maturity around five years old and can produce between 50,000 and 138,000 embryos per spawn. That is a considerable number, but most of these embryos, sadly, don't survive into adulthood.

A coconut crab can live up to 60 years old.

This crab is on the IUCN Red List of Endangered Species. The numbers of the population of these crabs are not exact. However, there is evidence that coconut crabs have declined by at least 30% over the past 60 years. Sadly, this trend is expected to continue for at least another 20 years. The main reason for this is because they are being caught for food more often. The most abundant coconut crab population is in places with a low or nonexistent human population.

Interesting Facts About These Crabs

The Coconut Crab: The Horrifying Behemoth Of Tropical Islands
  • They may be the reason Amelia Earhart's body was never found, as they eat carcasses and remains.
  • They're a type of hermit crab and they live in other crabs' shells until adulthood.
  • Coconut crabs have a strong sense of smell.
  • They also go by the name robber crabs due to their opportunistic feeding habits.
  • A coconut crab has the strongest claw pinch of any crustacean.
  • These crabs are hermits and prefer to live alone.