Walking the path at night, I hear near-constant rustling in the dried leaves. All along the route from my cottage to the shower block, I hear creatures scurrying away. Crabs. More crabs than I ever imagined possible.
Palmyra Atoll is a very remote island that is 1,000 miles south of Hawaii. I’m here for a fish research trip. Palmyra is a very crabby place. There are 12 kinds of land crabs here, and their numbers have been rising since rats were taken out.
Crabs also feature prominently in any Palmyra stay. Soon after landing on Palmyra, all researchers and visitors must attend an orientation to review safety rules. The remote island, administered by The Nature Conservancy and U. S. Fish and Wildlife Service, has no permanent inhabitants, so following rules and protocols is paramount. And one of the first rules you learn is a simple one: Watch your step. Watch every step.
This is in part for your safety; Palmyra is very, very far from medical assistance. But it’s also for the crabs. In the evenings, hermit crabs and other species come out en masse. The path is like an obstacle course with crustaceans as the theme. You need to wear a headlamp and be careful as you walk.
So I walk gingerly, shining my light on the path. Then I hear a much louder rustling. I swing my headlamp, and see a large form trundling through the leaf litter. This is no ordinary crab. It’s the one I’ve been looking for each evening: a coconut crab.
It’s a stunning creature, covered in blue-and-orange highlights, with an imposing claw waving in front. The crab is the size of a pie plate, and I know they can get much bigger.
It’s the biggest land crab and, really, the biggest land animal on Earth. It’s called the coconut crab. In many parts of the world, it faces a perilous future. On Palmyra, though, the situation is much brighter.
Crabs come in all shapes and sizes, from tiny pea crabs to giant Japanese spider crabs. But what is the biggest crab in the world and what are some other contenders for the largest crabs on Earth? Let’s take a look at the largest land and sea crabs to find out.
The Japanese Spider Crab – The Largest Crab in the World
The Japanese spider crab (Macrocheira kaempferi) reigns supreme as the largest crab in the world This massive crustacean is found in waters around Japan and has an incredible leg span reaching over 13 feet (4 meters). Their legs are spindly, giving them a spider-like appearance.
These giant crabs can weigh up to 40 pounds (18 kg) and have a body size of 15 inches (37 cm) wide. They use their long legs to walk along the seafloor and their hard shell and coloration help camouflage them against rocks and coral.
The Japanese spider crab is mostly active at night, when it scavenges for food like shellfish, dead animals, and plants. During the day, it will hide in holes and crevices to stay safe from predators.
The largest Japanese spider crab ever found had a leg span of 12 feet (3.7 meters)! It was nicknamed “Big Daddy” and lived to be a ripe old age of 100 years old.
Coconut Crab – The Largest Land Crab
While the Japanese spider crab rules the ocean, the coconut crab (Birgus latro) stands tall as the biggest land crab in the world.
These huge crabs live on islands in the Indian and Pacific Oceans. They grow to about 3 feet (1 meter) in length from leg tip to leg tip and can weigh up to 9 pounds (4 kg).
Coconut crabs get their name from their ability to climb trees and crack open coconuts with their strong claws. They can lift over 60 pounds with those powerful pincers!
But don’t let the name fool you. Coconuts are not their main food source. Coconut crabs mostly eat fruits, nuts, and smaller animals they find on the forest floor.
The size and strength of coconut crabs helps them defend against predators like rats and birds. Their numbers have increased on some islands after invasive species like rats were removed.
Giant Japanese Spider Crab vs Giant Coconut Crab
The Japanese spider crab lives in the ocean while the coconut crab lives on land, so they’d never meet in real life. But how would they compare if they ever came face to face?
While coconut crabs have an impressive strength that helps them crack coconuts, the Japanese spider crab’s larger size, longer reach, hard shell, and vice-like grip would likely give it an advantage in a pincer-to-pincer showdown. Those extra long, spindly legs don’t hurt either!
In reality, the only thing these two largest crabs in the world have to fear is humans and habitat loss.
Other Outsized Crabs to Watch For
While the Japanese spider crab and coconut crab take top honors for largest crab, here are some other giants of the crab world:
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Tasmanian giant crab – This crab off Australia’s coast weighs up to 20 pounds (9 kg) and measures 18 inches (46 cm) wide.
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Alaskan king crab – The famous red king crab of Alaska has a leg span over 5 feet (1.5 m) and can weigh 28 pounds (13 kg).
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Snow crab – Found in icy northern waters, male snow crabs grow to 6.5 inches (16.5 cm) wide and weigh around 3 pounds (1.4 kg).
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Giant mud crab – This crab from Asia measures over 11 inches (28 cm) wide and exceeds 11 pounds (5 kg).
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Red rock crab – Growing up to 6 inches (15 cm) wide and 4 pounds (1.8 kg), this crab lives along North America’s western coast.
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European spider crab – With their spiny shells reaching 7 inches (18 cm) wide, these crabs resemble undersea spiders.
So if you’re ever diving near Japan and see a giant crab bigger than your torso, it just might be the world’s largest crustacean – the Japanese spider crab! And if you’re exploring a tropical island and spot a massive land crab, watch your fingers, because it could be a powerful coconut crab!
Life as a Coconut Crab
A coconut crab will also run away when a person comes close, but if you move quietly toward it, it will stop and look at you for a long time. Up close, a coconut crab looks like a supersized version of a hermit crab, minus the shell.
That is actually the case: hermit crabs and coconut crabs are closely related. Like the hermit crabs you see in pet stores, coconut crabs live in their shells when they are young. As they get older, they abandon the shell and instead rely on their tough exterior for protection.
These are truly land crabs. Male coconut crabs only go into the water to lay eggs, which is the first step in the larval stage.
Unlike hermit crabs, they grow large. Very large. They can live for sixty years and grow to be three feet across and nine pounds heavy as adults.
Then there’s that claw. Stories have long been told about the crab’s finger-crushing abilities. Recent research quantified that power. A crab can squeeze with a crushing force of 3000 newtons, or about 675 pound per square inch. Compare that to a lobster, which has a crushing force of 250 newtons.
Coconut crabs can also lift more than 60 pounds, and yes, they can crush through coconuts. People think that this species likes to eat coconuts because of this, but that’s not really the case. Coconut crabs are scavengers and opportunists. They eat primarily fruits, nuts and the pith of fallen trees, but will also eat carrion. On Palmyra, they actively hunt prey, especially other crabs.
People also call them “robber crabs” because they will eat almost anything and take things people leave outside. Colorful stories abound, including one where a crab carried off a full whiskey bottle. Unlike, say, a pack rat, the coconut crab is not stealing shiny objects. Rather, it’s likely related to the crab’s excellent sense of smell. Animals that move around at night or in the dark rainforest need to be able to smell things very well to find food. Human objects with a trace of food are thus carried off.
Coconut crabs are found widely in coastal habitats around the Pacific and Indian oceans. In many parts of their range, populations are declining. As reported this year in Mongabay, in some areas, coconut crabs have disappeared completely.
The crabs face a predictable litany of threats. Coconut crabs always live near the coast, often in forest habitats – areas that are often developed. Additionally, people eat coconut crabs so they are vulnerable to overharvesting. On many Pacific islands, they’re a difficult species to see.
That’s not the case on Palmyra. It’s actually easier to see coconut crabs now than it was just a few years ago, thanks to a huge success in protecting them.
Of Crabs and Rats
Palmyra Atoll is a naturalist’s wonderland, with so many creatures to capture your attention. There are manta rays and gray reef sharks, sea turtles and huge colonies of birds. And fish of every conceivable size and color. With all these charismatic species around, it might seem hard for an invertebrate to win anyone’s heart.
But the crabs hold their own.
In part, it’s because they’re everywhere. There are the strawberry hermit crabs patrolling the beaches, and little fiddlers darting into burrows. There are a crazy number of crabs at the food waste pit (any food waste is eaten within hours), outside your cottage, and near the docks.
The coconut crab is the star, and a night-time crab walk will usually yield at least a few. U. S. Fish and Wildlife staff lead a weekly “crab walk” for visiting researchers and Palmyra’s seasonal staff. It’s a popular activity as the group attempts to see all 12 land crab species in an evening. Still, the coconut crab steals the show.
Seeing all these crabs, amidst this biological richness, it’s easy to call Palmyra Atoll a “pristine” environment. But that may be a bit misleading. Palmyra’s known history of human habitation is indeed fairly recent. Notably, it was a U. S. Naval base during World War II. The human presence now seems minimal, but that’s not the same as non-existent. People have caused significant impacts. Chief among those: rats.
Rats arrived, as they often do, on ships. They quickly began eating their way through Palmyra’s terrestrial biodiversity. People who worked on the island ten or twenty years ago say that rats’ feet are always moving through the trees and on roofs.
Rats are bad for island wildlife, a fact well established in too many islands around the globe. Many conservationists know they are hell on birds. They eat eggs and nestlings, devastating seabird colonies.
Less known is that invasive rats also devastate crab populations. With its sharp claws and great strength, a coconut crab might look like a very dangerous enemy for a rat. That’s true. Rats mainly don’t bother with adult crabs. They focus on the young crabs. With adult crabs living for decades, they persisted on Palmyra, but few young crabs survived.
In 2011, The Nature Conservancy, U. S. Fish and Wildlife Service and Island Conservation partnered to rid Palmyra of rats. It’s a success story environmental writer Ted Williams has called “the miracle on Palmyra. “The latest science and technology made it possible to achieve a goal that no one had thought possible before: getting rid of every rat on the island.”
It worked. In 2015, Palmyra was proclaimed “rat free.”
Since then, several land crab populations have increased 450 percent. There are two species of tree crabs that researchers didn’t even know existed on Palmyra. They were first documented two years after rat eradication; now they are everywhere.
Coconut crab young are surviving. I often found coconut crabs scuttling away just a short distance from the research base.
Top 10 Largest Crabs In The World
FAQ
What is the largest land crab in the world?
How big is a giant crab?
Which country has the biggest crab?
Can you eat a spider crab?
What is the biggest crab in the world?
Either way, a steady diet can assist certain crab species in growing to incredible sizes. The biggest crab in the world, the Japanese spider crab, is capable of achieving a leg span of more than 13 feet (4 meters) across. Read on to get better acquainted with the Japanese spider crab, plus discover eight more of the largest crabs out there.
How much does a giant crab weigh?
The Tasmanian giant crab is one of the largest crabs in the world, reaching a mass of 17.6 kg (39 lb) and a carapace width of up to 46 cm (18 in). Among crabs, only the Japanese spider crab ( Macrocheira kaempferi) can weigh more.
Which crab has the longest leg span?
The spider crab resides in the waters surrounding Japan, and it has the longest leg-span of all the arthropods. These crabs are a delicacy and therefore are subjected to the fishery. Japanese spider crab has an 18 ft leg span from claw-to-claw, and its body can grow up to 16 inches in carapace-width. The spider crabs weigh about 42 lbs.
How big is a coconut crab?
Known for its surprising ability to climb coconut trees, the coconut crab can reach a leg span of about 40 inches (1 meter) from leg tip to leg tip and can weigh 10 pounds (4.5 kg). This makes it the largest land crab in the world.