Coconut crabs are fascinating creatures that have captured people’s imaginations for centuries. Their massive size and tree-climbing abilities make them seem almost mythical. But just how big do these giant hermit crabs get? In this article, we’ll explore the sizes of coconut crabs and what makes them the world’s largest land arthropod.
A Look at Their Impressive Dimensions
Coconut crabs can grow to be truly enormous. The largest individuals can measure 3 feet across and weigh up to 9 pounds To put that into perspective, that’s about the size of a small dog! Their legs can span up to 3 feet long.
Most coconut crabs are not quite that big though. Their bodies typically measure 9-16 inches long. Male coconut crabs are generally larger than females. They can have a leg span reaching over 3 feet, while females may have a span of about 2 feet.
Exploring Why They Grow So Large
There are several reasons why coconut crabs get so massive compared to other hermit crabs
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Diet – Coconut crabs eat a nutritious diet high in fat and protein. This includes coconuts nuts, seeds fruits, and even carrion and other crab species. Their food sources allow them to grow quite large.
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Age – These crabs are very long-lived. They can survive over 60 years in the wild. Their long lifespans allow them to just keep growing.
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Lack of predation – With their formidable claws and armor-like exoskeletons, adult coconut crabs have few natural predators to threaten them. This removes obstacles to their growth.
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Terrestrial habitat – Since coconut crabs live on land rather than in the ocean, the constraints of buoyancy and hydrodynamics do not apply. This frees them to evolve massive bodies.
Their large size gives coconut crabs several advantages. Their powerful claws can easily open coconuts and other tough foods. Their strength deters predators. And their bulk helps them survive the rigors of land living. Overall, their giants proportions help coconut crabs thrive in their island habitats.
Young Coconut Crabs – How Small Do They Start?
In contrast to their intimidating adult size, baby coconut crabs start out quite small. The larvae are only about 1⁄8 inch (2-3 mm) long when they hatch from the eggs. After a month floating in the ocean, the young crabs settle to the shore. At this juvenile stage they inhabit small seashells for protection.
As they grow, the crabs graduate to larger and larger shells. Once they reach sexual maturity at 5-8 years old, they abandon shell use. At this point the crabs have grown to about 2 inches (5 cm) long. Their full giant size won’t be attained until 10-15 years of age.
So while coconut crabs end up bulky, they begin life just like other crab species – tiny larvae floating in the ocean. Their spectacular growth occurs over a long period of development.
How Do Coconut Crabs Compare to Other Crabs?
To appreciate the impressive dimensions of coconut crabs, it helps to look at how they size up against other crab species:
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Coconut crabs are about 5-10 times larger than many common shore crabs like fiddler crabs.
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They absolutely dwarf hermit crabs, being 50-100 times heavier than most tropical hermit species.
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The largest coconut crabs are 2-3 times wider than king crabs, the giants of aquatic crab species.
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Coconut crab legs can be twice as long as those of enormous Japanese spider crabs, the biggest arthropods in ocean environments.
So whether compared to fellow land crabs or their marine cousins, coconut crabs stand out in terms of sheer bulk and leg span. Their size makes them unique among the approximately 4500 brachyuran crab species inhabiting our planet.
Leg Span vs. Body Size
When considering their size, it’s important to distinguish between coconut crabs’ leg span and their actual body dimensions. The leg span measurement can make them seem even more giant!
For example, a coconut crab with a 16 inch body size may have a leg span exceeding 3 feet. But its body would only be about the size of a bowling ball.
So while they appear far larger with legs extended, the crabs’ bodies are still quite a bit smaller. Keep this in mind when thinking about their overall size. Body measurements give a more accurate sense of their mass.
Exceptions – Abnormally Large Specimens
While the sizes discussed so far are typical, occasionally giant coconut crabs are found that exceed all expectations. The largest on record had a 4 foot leg span and weighed over 17 pounds.
These super-sized specimens are quite rare. Only 1 out of 100,000 coconut crabs ever surpass the 3 foot leg span benchmark. Their enormous proportions result from genetic outliers, ideal habitat conditions, and luck in avoiding predators during their long lives.
For coconut crabs, the potential for growth seems limitless. Who knows what monstrous sizes they could attain if allowed to live free of human pressures? We can only imagine what the upper limits might be for these incredible creatures.
Up in the trees
Adult coconut crabs live on land, returning to sea only to release their fertilized eggs. They live alone in their burrows, where they usually stay during the day, avoiding the heat and preventing water loss. Even though they are more active at night, on Tetiaroa, especially in the forest of motu Reiono, we often see them up in the trees during daytime hours.
“There is a land crab that you can figure generally on being twice as big as your head. These creatures have very powerful claws and they can open a coconut by crushing the shell. They are also delicious to eat, but should they find their way into your bed, you would be advised to leave immediately. They will fasten onto whatever part of the body is available and their grip can only be released by tickling their behinds.”
Excerpt from M.B’s notes for his atoll, Tetiaroa.
The above excerpt from M.B’s notes for his atoll, Tetiaroa, is a perfect summary of what characterizes a coconut crab.
The most striking thing about these crabs is how big they can grow, which gives them the distinction of being the largest land crabs in the world. The biggest coconut crab ever recorded had a 1m (3ft) leg span and weighed 17 kg. They are also extremely powerful, their claws are strong enough to cut open a coconut to eat it, hence their name.
“Robber crabs” is another name they go by because of their opportunistic behaviour. They prefer coconut flesh or fruits, but they will also eat almost whatever they come across : birds, other crabs, turtles, rats… They have even been seen in kitchen sinks, trying to scrape leftovers from dishes. They have a powerful sense of smell.
The Colossal Coconut Crab | South Pacific | BBC Earth
FAQ
Has anyone been eaten by a coconut crab?
A popular Internet meme suggests that Amelia Earhart crash-landed on Nikumaroro and her remains were rapidly consumed by coconut crabs on the island. However, as no evidence of Earhart’s plane has been found on or near Nikumaroro, this theory is generally discredited by historians.
Is a coconut crab bigger than a Japanese spider crab?
They’re not quite the world’s largest crab – that would be the Japanese spider crab, Macrocheira kaempferi, which can reach a whopping 3.7 metres from claw to claw. But the coconut crab is the largest crustacean that spends all its adult life on land, with a Guinness World Record opens in a new window to prove it.