35 Facts About Coconut Crab

Meet the Coconut Crab

The coconut crab, scientifically known as Birgus latro, is a fascinating creature with unique adaptations and behaviors. Let's dive into some intriguing facts about this remarkable species.

1. Scientific Name and Common Names
   The coconut crab is scientifically known as Birgus latro. It is also called the robber crab or palm thief due to its habit of stealing food and other items.

2. Largest Terrestrial Arthropod
   Weighing up to 4.1 kg (9 lb) and boasting a leg span of up to 1 meter (3 ft 3 in), the coconut crab holds the title of the largest terrestrial arthropod.

Where They Live

Coconut crabs are found in specific regions across the globe. Their distribution and habitat preferences are quite interesting.

3. Distribution
   These crabs inhabit tropical islands in the Indian and Pacific Oceans, including the Gambier Islands, Pitcairn Islands, Caroline Island, and Zanzibar. They have been extirpated from areas with significant human populations, such as mainland Australia and Madagascar.

4. Genus and Related Species
   Belonging to the genus Birgus, coconut crabs are related to other terrestrial hermit crabs of the genus Coenobita.

Adaptations for Land Life

Coconut crabs have evolved several unique adaptations that allow them to thrive on land.

5. Adaptations to Life on Land
   They possess branchiostegal lungs for breathing air and a tough exoskeleton on their abdomens, which develops after the juvenile stage.

6. Juvenile Stage
   Juvenile coconut crabs use empty gastropod shells for protection, similar to other hermit crabs. As they grow, they develop a hardened exoskeleton and stop carrying shells.

What They Eat

Coconut crabs have a varied diet that includes both plant and animal matter.

7. Diet
   Adult coconut crabs are omnivores, primarily feeding on fleshy fruits, nuts, seeds, and the pith of fallen trees. They also consume carrion and other organic matter opportunistically.

8. Omnivorous Diet
   Their diet includes fruits like Ochrosia ackeringae, Arenga listeri, Pandanus elatus, and P. christmatensis; nuts like Aleurites moluccanus; drupes like Cocos nucifera; and seeds like Annona reticulata.

Predation and Competition

Coconut crabs face various threats and competition in their natural habitat.

9. Predation and Competition
   Sea birds prey on young crabs, while larger, older crabs eat crabs of all ages. Competition may exist between coconut crabs and other terrestrial crabs with similar habits, such as the Coenobita species, although this is usually indirect.

Climbing and Burrowing

Despite their size, coconut crabs are adept climbers and burrowers.

10. Climbing Ability
    Coconut crabs can climb trees, including coconut and pandanus trees, although they do not selectively pick coconut fruit. They might dislodge ripe fruit that would otherwise fall naturally.

11. Escape Mechanism
    Climbing serves as an immediate escape route from predators when not near their burrows.

12. Burrowing Behavior
    Despite their climbing ability, coconut crabs primarily live in burrows, which serve as their primary shelter and hiding place.

Physical Characteristics

Coconut crabs have distinct physical features that set them apart from other crabs.

13. Physical Characteristics
    Adult coconut crabs can be any shade from pale violet to dark brown or deep purple. Juveniles and young adults are brown with black stripes along their legs. The chelae (claws) are asymmetrical, with the left being more prominent than the right.

14. Sexual Dimorphism
    Males are larger than females, with an average carapace length of 75 mm compared to 50 mm for females. Females have three large, feathery pleopods on their abdomens for transporting egg masses.

Breathing and Senses

Coconut crabs have unique adaptations for breathing and sensing their environment.

15. Breathing Mechanism
    They use branchiostegal lungs for breathing air, making them vulnerable to drowning if immersed in water for too long.

16. Sense of Smell
    Coconut crabs have a highly sensitive sense of smell, which they use to find food and even blood. Up to 40% of their brain is dedicated to this sense.

Food Acquisition

Coconut crabs have developed interesting methods for acquiring and consuming food.

17. Food Acquisition
    They can take coconuts from the ground, cut them to a husk nut, and carry the husk nut up a tree to access the coconut flesh inside. They often descend from trees by falling and can survive a fall of at least 4.5 meters (15 ft) unhurt.

18. Opening Coconuts
    To open coconuts, coconut crabs use their strong claws. They can either drop the coconut from a tree and repeatedly strike it with their pincers, piercing the husk and splitting the seed, or they can use their claws to puncture the coconut through the “eyes,” causing it to split.

Cultural Significance

Coconut crabs hold cultural importance in various regions.

19. Cultural Significance
    They have various cultural names across different regions. In the Cook Islands, they are known as “unga” or “kaveu,” while in the Mariana Islands, they are called “ayuyu.” Other common names include giant coconut crab, robber crab, and palm thief. In Japan, the species is referred to as “yashigani,” meaning “palm crab”.

20. Traditional Beliefs
    In some cultures, there are traditional beliefs that ancestral spirits can return to the terrestrial world in the form of animals like the coconut crab. This belief highlights the significant cultural value placed on these creatures.

Conservation Status

Understanding the conservation status of coconut crabs is crucial for their protection.

21. Conservation Status
    The International Union for the Conservation of Nature and Natural Resources has classified coconut crabs as “data insufficient.” While they are not currently threatened or endangered, their slow growth rate and ease of capture make them vulnerable to overharvesting.

Ecological Role

Coconut crabs play an important role in their ecosystems.

22. Habitat Dispersal
    Coconut crabs help disperse the seeds of coconut trees by scavenging the fruit and discarding it rather than taking it back to their burrow to eat. This behavior aids in the spread of coconut palm populations.

23. Predator Avoidance
    Adult coconut crabs live alone in crevices or burrows and aggressively guard their privacy. A crab entering another’s burrow risks becoming a meal. They also maintain personal space by ritualized claw waving when they emerge to feed.

Reproduction and Survival

The reproductive behavior and survival rate of coconut crabs are fascinating aspects of their life cycle.

24. Reproduction
    After mating, females attach their eggs to special appendages and carry them under their abdomens. While the young develop inside the eggs, the females hold onto them, sticking near the edge of the sea so that they can periodically moisten the eggs. This care ends when the young are ready to hatch, at which point the females release their hatchlings into the ocean waves.

25. Survival Rate
    Only a few of the released hatchlings will survive to return to land. This low survival rate highlights the challenges faced by young coconut crabs in their early stages of life.

Historical and Scientific Significance

Coconut crabs have been known to scientists for centuries and have even been linked to historical mysteries.

26. Scientific Discovery
    Western scientists have known about the coconut crab since 1580. In 1705, Carl Linnaeus named the crab “Cancer latro,” with the latter part being Latin for “robber”.

27. Famous Disappearance Theory
    The broad diets of coconut crabs have led to the theory that famous aviator Amelia Earhart was never found because she was eaten by coconut crabs on Nikumaroro Island. However, no evidence supports this claim.

Color and Toxicity

Coconut crabs exhibit color variations and can become toxic under certain conditions.

28. Color Variation
    Coconut crabs come in either red or blue, but scientists aren’t quite sure what causes the difference. Studies have shown that it isn’t associated with the crab’s sex, size, or pincer strength. One explanation is that it could be for assortative mating or sexual selection.

29. Toxicity
    While coconut crabs are not poisonous, they can become poisonous by eating certain toxic foods like the sea mango, a coastal tree that is extremely toxic to humans.

Strength and Behavior

Coconut crabs are known for their impressive strength and unique behaviors.

30. Grip Strength
    The pincers of a coconut crab are strong enough to cause pain to humans and can generate a maximum of 3,300 newtons of force. Their grip is 10 times greater than a human’s, making them formidable opponents.

31. Escape Mechanism
    To loosen a coconut crab’s grip, Micronesians of the Line Islands suggest tickling the soft underparts of the body. This unique method highlights the crab’s sensitivity to touch.

32. Tree Climbing
    Coconut crabs have been observed climbing trees to disable and consume prey. In one instance, a large coconut crab was observed climbing a tree to disable and consume a red-footed booby on the Chagos Archipelago.

33. Organized Attacks
    In the Chagos Archipelago, coconut crabs were observed playing out an organized, direct attack on an adult red-footed booby by sneaking up its tree under the cover of night. This behavior showcases their intelligence and strategic hunting.

Swimming and Scientific Study

Despite their fascinating nature, coconut crabs have limitations and require further study.

34. Swimming Ability
    Adult coconut crabs are unable to swim. Their inability to swim as adults makes their widespread distribution across the oceans a mysterious prospect. Most scientists concur that they must have colonized the islands as planktonic larvae.

35. Scientific Study
    Despite their fascinating nature, coconut crabs are little-studied creatures. They may be huge and heavily armored, but they can be vulnerable to introduced predators like rats and habitat loss. The International Union for Conservation of Nature lists the coconut crab as data deficient, emphasizing the need for further study and conservation efforts.

The Fascinating World of Coconut Crabs

Coconut crabs, with their impressive size and unique adaptations, are truly remarkable creatures. From their status as the largest terrestrial arthropods to their ability to climb trees and open coconuts, these crabs showcase nature's ingenuity. Found across tropical islands in the Indian and Pacific Oceans, they have a varied diet, including fruits, nuts, and even carrion. Their strong pincers, capable of generating 3,300 newtons of force, make them formidable. Despite their fascinating traits, they face threats from habitat loss and overharvesting. Their cultural significance and intriguing behaviors, like their climbing and burrowing habits, add to their mystique. Understanding these facts highlights the need for further study and conservation efforts to protect these incredible creatures. The coconut crab's story is a testament to the wonders of nature and the importance of preserving such unique species.