How do adult coconut crabs breathe?

With lungs made from the gill-chamber lining

Where does a coconut crab start opening a coconut?

At the end with the three eye-holes

It waits for the coconut to rot

Coconut crab

Birgus latro

The coconut crab (Birgus latro) is the largest arthropod that lives on land, weighing up to 4 kg with a leg span of about 1 m. A close relative of land hermit crabs, it lives on islands across the Indian and Pacific oceans, breathes air with special lungs and goes back to the sea only to release its eggs. It is listed as Vulnerable on the IUCN Red List, mainly because people have harvested it heavily for food.

Also known as Robber crab, Palm thief, Giant robber crab

Coconut crab abilities

3,300 N estimated pinch of a 4 kg crab
No crustacean measured so far pinches harder. Scientists estimate a 4 kg giant could squeeze with about 3,300 N.
- Researchers in Okinawa measured 29 wild crabs from 33 g to 2.1 kg. Their strongest pinches ranged from 29 N to 1,765 N.
- Bigger crabs pinch harder. Scaling up to the biggest known crab of 4 kg gives about 3,300 N.
- That is stronger than the bite of most land predators that have been measured, with alligators as the exception.
- Red and blue crabs pinch equally hard.
Coconut crab pinch force
4 kg crab (estimate)3,300 N
Strongest of 29 crabs (measured)1,765 N
Weakest of 29 crabs (measured)29 N
Measured on the left claw of 29 wild crabs (33 g to 2.1 kg) in Okinawa; the 4 kg value is an estimate from the same study.
Sources [2, 9]
≈30 kg weight it can lift
Strong enough to lift about 30 kg, the coconut crab climbs tree trunks with pointed leg tips that grip the bark.
- Its lifting strength has been reported at 28–30 kg, about seven times its own top weight.
- It climbs trees to reach food. By day it usually stays hidden in a burrow and comes out at night.
- On the Chagos Islands, a scientist watched one climb a tree at night to reach a seabird sleeping on a low branch.
Sources [1, 2, 6, 10]
3 eye-holes where it starts on a coconut
It tears off the husk strip by strip, starting at the end with the coconut’s three ‘eyes’, then hammers one eye open with a claw.
- Charles Darwin described the method in 1845 on the Keeling Islands: fibre by fibre, always from the end with the three eye-holes, then hammering until a hole opens.
- Coconuts are only part of the menu. Fallen fruits such as pandanus are a main food in many places, plus dead animals and other crabs.
- A freshly opened coconut can attract several crabs, drawn by its smell.
Sources [1, 5, 15]
≈40% of its brain’s nerve tissue handles smell
Moving from sea to land meant learning to smell in air. The coconut crab’s antennules ended up working a lot like an insect’s antennae.
- In water, smells are dissolved. In air, they float as tiny gas molecules, so a land nose needs different equipment.
- On a Christmas Island beach, scientists tested 15 smells found in coconuts and arenga fruit. Only one, acetoin, attracted crabs.
- Smell centres fill about 40% of its brain’s nerve tissue, with more than 1,000 tiny smell-sorting knots on each side. Scientists call it an ‘insect nose’ that evolved separately.
Sources [1, 4, 5, 7]
0 working gills in adults
A crab that would drown in the sea. Grown coconut crabs breathe air with lungs built from the lining of their gill chambers.
- The lung lining is thin, packed with blood vessels and folded into a big surface for taking in oxygen.
- The gills are only small leftovers that do not help with breathing.
- The lungs develop as the young crab changes shape and moves onto land. After that it can never go back to living in the sea.
Sources [1, 4, 11]
3–16 weeks hidden in a burrow to moult
To grow, a coconut crab must shed its hard outer skeleton. It digs a burrow, hides for weeks and then eats its old skin.
- Moulting burrows can be up to 1 m long. Big crabs take longer to finish than small ones.
- Once the new skeleton hardens, the crab eats the old one, recycling its minerals.
- In Okinawa, most crabs moulted in winter, except young ones and the very largest.
Sources [1, 8]
51,000–138,000 eggs released by one female
A land animal that starts life in the ocean. Females walk to the shore and shake their eggs into the sea, where they hatch at once.
- Release happens in the evening at the highest tides, a few days after a new or full moon, so the surf carries the larvae out to sea.
- The larvae drift in the plankton for about 17–28 days. In the lab, none survived at 18.9 °C, while more than 80% made it at 27–30 °C.
- Next, each young crab finds an empty snail shell and crawls ashore, never to live in the sea again.
Larvae surviving to the next stage, by water temperature
27.0 °C85.6%
29.8 °C82.2%
18.9 °C0%
Laboratory study (Hamasaki et al. 2009).
Sources [1, 10, 11, 16]
2019 first study of its soundsStill debated
Coconut crabs make tapping sounds with a paddle inside their breathing chamber. What the sounds mean is still unclear.
- X-ray video showed the sound comes from the scaphognathite, a paddle that normally pumps air over the lungs.
- The pitch and the gaps between taps vary, even in the same crab.
- Crabs in captivity made different sounds at different stages of courtship, but scientists have not yet shown what each sound is for.
Sources [14]

Tap a pin on the model or a part below.

1,765 N strongest pinch measured
- The two big claws are not the same size: the left one is usually larger.
- In a study of 29 wild crabs in Okinawa, Japan, weighing 33 g to 2.1 kg, the strongest pinch was 1,765 N. Bigger crabs pinched harder.
- Claws and walking legs have a thicker, strongly mineralised outer skeleton than the rest of the body.
Sources [1, 2, 3]
Insect-like sense of smell
- The long antennae are feelers. The short antennules are its nose: they pick up smells and can tell different odours apart.
- Smelling in air is very different from smelling in water. Scientists found the coconut crab’s smell sense works a lot like an insect’s.
- A smell called acetoin, found in coconuts and arenga palm fruit, draws crabs in.
Sources [1, 4, 5]
≈1 km carried away, then found its way home
- Coconut crabs are mostly active at night. On islands with lots of people they come out only after dark.
- On Christmas Island, scientists fitted GPS tags to crabs. Crabs moved away about 1 km found their way back home.
- Smell centres fill about 40% of its brain’s nerve tissue, which fits an animal that finds food by nose.
Sources [1, 6, 7]
485 crabs told apart by their grooves
- The hard shield over the front of the body is called the carapace. Its pattern of grooves is different in every crab.
- In Okinawa, researchers photographed 485 crabs and recognised them again by their grooves, like fingerprints.
- Colours range from red-orange to blue-purple. In three studied places about 3 in 4 crabs were red.
Sources [8, 9]
- The abdomen is tucked under the body, like a hermit crab’s soft tail end.
- Young crabs protect it inside a borrowed snail shell. Adults leave shells behind and grow hard plates instead.
- Being free of a shell is one reason coconut crabs could grow so much bigger than their hermit crab cousins.
- Scientists think a gene that is unusually common in its DNA may help harden the adult abdomen so it dries out less on land.
Sources [1, 2, 10, 11]
≈1 m leg span
- Pointed leg tips grip tree bark, so the crab can climb trees to find food.
- From leg tip to leg tip, a big coconut crab spans about 1 m.
- The last pair of legs is small and hard to see. Females use it to look after their eggs.
Sources [1, 6, 10]
- Its gills are tiny and barely work. It breathes air with lungs made from the lining of its gill chambers.
- That lining has a huge, thin surface full of blood vessels, so oxygen passes in easily.
- Only the larvae live in water. A grown coconut crab drowns if it is kept under water.
Sources [1, 4]
- It eats fallen fruit such as pandanus, coconut flesh and dead animals, and sometimes catches live prey such as red crabs. It prefers foods rich in fat, sugar or protein.
- After moulting, it eats its own old outer skeleton.
- Near its mouth, a paddle that pumps air through the breathing chamber can also tap out sounds.
Sources [1, 12, 13, 14]
≈100,000 eggs in a batch
- A female carries a mass of orange eggs under her abdomen, often around 100,000 of them.
- She keeps them clean and aerated for about 25–29 days, then releases them into the sea.
Sources [1]

Real coconut crabs

Photos from Wikimedia Commons. Four of them can repaint the 3D model.

Red-orangeRed-orange to brick-red body and legs with paler joints.About 3 in 4 crabs in studies on Pemba, Chumbe and Christmas IslandRed-orange coconut crab on Christmas Island, home to one of the largest populations. Photo: DIAC images, CC BY 2.0
Blue-purpleDeep blue to purple body with blue-grey legs.About 1 in 4 crabs in the same studies; no difference in size, sex, pinch or behaviourThe blue-purple colour form, photographed on Niue. Photo: Pseudopanax at English Wikipedia, Public domain
JuvenileA small crab with its soft abdomen tucked into a borrowed snail shell, like a hermit crab.Uses shells until hard plates grow; some drop them at 8.4 mm body length, others still carry them at 11.3 mmA juvenile wearing a snail shell, just like a hermit crab. Photo: drew_avery, CC BY 4.0
Female with eggsSmaller than a male, with an orange egg mass held under the abdomen on feathery swimmerets.Average body length about 50 mm, against 75 mm in males; carries eggs for about 25–29 daysA female coconut crab climbing a palm trunk in the Togian Islands, Indonesia. Photo: Neisyaranifauzia, CC BY-SA 4.0
On Dolly Beach, Christmas Island, after opening a coconutPhoto: John Tann, CC BY 2.0
Big claws on Palmyra Atoll National Wildlife RefugePhoto: Ryan Hagerty / USFWS Pacific, Public domain
Legs spread on Diego Garcia, Chagos IslandsPhoto: Drew Avery, CC BY 2.0
On the Zanzibar Archipelago, Tanzania, where scientists monitor 15 sitesPhoto: Leonel Roget, CC BY 4.0
Out for a walk on Christmas IslandPhoto: Donna Belder, CC BY 4.0

Coconut crab by the numbers

Measured by scientists in the wild and in the lab, with comparisons you can picture.

Weight: up to 4 kg; the heaviest arthropod living on land; Coconut crab (max)4 kgJapanese spider crab (max)20 kg; A sea-floor spider crab can be about 5 times heavier⁠[4, 6, 10, 17]
Leg span: ≈1 m; from one leg tip to the other⁠[6, 10, 1, 17]; Coconut crab1 mJapanese spider crab3.7 m
Pinch force: 1,765 N; strongest of 29 wild crabs measured; about 3,300 N estimated for a 4 kg crab⁠[2]; Strongest measured1,765 NEstimated (4 kg crab)3,300 N
Lifting strength: 28–30 kg; reported weight it can lift; About 7 times its own top weight⁠[2, 6]
Lifespan: up to 60 years; reaches full size only after 40–60 years⁠[6, 1]
Grown up at: ≈5 years; average age at first breeding⁠[1]
Eggs per batch: 51,000–138,000; about 100,000 on average⁠[1]
Time at sea: ≈5–8 weeks; 17–28 days as drifting larvae, then 21–28 days as a shell-seeking glaucothoe⁠[1]
Moulting hideout: 3–16 weeks; in a burrow up to 1 m long⁠[1]
Red to blue: ≈3 : 1; red-orange to blue-purple crabs on Pemba, Chumbe and Christmas Island⁠[9]

Coconut crab myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“The coconut crab is the biggest crab in the world.”
“A big coconut crab pinches harder than most land predators bite.”
“Coconut crabs eat only coconuts.”
“Coconut crabs are good swimmers.”
“Young coconut crabs live in shells, like hermit crabs.”
“Coconut crabs climb palms to drop coconuts and crack them on the ground.”
“Coconut crabs ate the pilot Amelia Earhart.”
“Robber crabs steal shiny things from people.”

Coconut crab records

Superlatives and record holders, each checked against its source.

Largest land-living arthropod
up to 4 kg
Coconut crab
with a leg span of about 1 m⁠[4, 6, 10]
Strongest crustacean pinch measured
1,765 N
Coconut crab
measured; about 3,300 N estimated for a 4 kg crab⁠[2]
Largest arthropod by leg span
up to 3.7 m
Japanese spider crab
lives on the sea floor off Japan⁠[17]
First large-scale GPS study of an arthropod
55 crabs tagged
Coconut crabs of Christmas Island
showing homing and trips of several kilometres⁠[6]
Northernmost population
26°41′N
Okinawa, Japan
Ocean Expo Park, home to the crabs measured for pinch force⁠[8, 2]

A coconut crab’s life

From an egg shaken into the sea to a giant that may live for 60 years.

Night 0
Into the sea
On an evening high tide near a new or full moon, the mother shakes her eggs into shallow water. They hatch as they touch it.⁠[1]
Weeks 1–4
Drifting larva
The larvae drift through 4–5 stages for about 17–28 days, feeding on plankton. They need warm water.⁠[1, 16]
Weeks 4–8
Shell hunter
As a glaucothoe, the young crab finds an empty snail shell and settles in shallow water near the shore.⁠[1, 11, 10]
≈2–3 months
Land crab
Over about 3–4 weeks it changes into a tiny crab and moves onto land. Its lungs develop, and it will never live in the sea again.⁠[1, 11]
First years
Shell wearer
It keeps wearing snail shells until hard plates protect its abdomen, then lives shell-free.⁠[1, 10]
Most years
Moult
To grow, it hides in a burrow for 3–16 weeks, sheds its skeleton and eats the old one.⁠[1, 8]
≈5 years
Grown up
It is old enough to breed. Females carry around 100,000 eggs for about 25–29 days.⁠[1]
40–60 years
Full size
Growth is slow, so it reaches full size only after decades. Some may live to 60.⁠[1, 6, 8]

Coconut crab vs land hermit crab vs Japanese spider crab

The coconut crab’s closest relatives wear shells all their lives. The biggest crab of all lives in the deep sea.

Coconut crab vs land hermit crab vs Japanese spider crab
	Coconut crab	Land hermit crab	Japanese spider crab
Scientific name⁠[19, 2, 17]	Birgus latro	Coenobita (several species)	Macrocheira kaempferi
Lives⁠[1, 10, 17]	On land, on Indian and Pacific Ocean islands	On land, on tropical coasts	On the sea floor off Japan, 50–600 m deep
Size⁠[6, 10, 17]	Up to 4 kg, leg span ≈1 m	Small enough to fit in a snail shell	16–20 kg, leg span up to 3.7 m
Shell⁠[10, 2, 17]	Snail shell only when young; adults go shell-free	Borrowed snail shells for life	Its own hard, spiny shell
Breathes⁠[1, 4, 10, 17]	Air, with lungs; drowns under water	Air, as an adult on land	Water, on the sea floor
Starts life⁠[1, 10, 17]	As a larva in the sea	As a larva in the sea	As a larva in the sea

Land hermit crabs (Coenobita) are the coconut crab’s closest living relatives. Coconut crabs probably split from a shell-wearing hermit crab ancestor 2.6–5.3 million years ago.

Meeting a coconut crab safely

Coconut crabs are not aggressive, but a big one can give a very strong pinch.

1,765 N
pinch measured
Never touch or pick one up. Watch from a distance, and tell an adult if one is near your tent or bag.⁠[2]
Night
when they come out
They are most active after dark. Use a torch, stay on paths and follow the island’s rules for watching wildlife.⁠[1]
Toxic food
can pass to the crab
Crabs that have eaten poisonous sea mango fruit have made people seriously ill in New Caledonia and Japan. Doctors can treat it, but it is one more reason to leave coconut crabs alone.⁠[20, 21, 22]

Are coconut crabs endangered?

They are Vulnerable. Slow-growing and easy to catch, coconut crabs have vanished from many islands where people collect them for food.

IUCN Red List

Vulnerable (VU)

Population decreasing

Once common on tropical islands of the Indian and Pacific oceans, they are now declining in most places and locally extinct in many parts of their old range.⁠[23, 19, 6, 10]

IUCN Red List (via GBIF and Wikidata, 2026)

Threats

Overharvesting
They are collected for food. Because they grow slowly and are easy to catch, too many can be taken quickly.⁠[1, 10]
Big males taken first
In Japan’s Ryukyu Islands, large males are now rare and some populations are mostly female.⁠[24]
Small, scattered homes
They live on small islands, and on many of them harvesting has already wiped them out. Habitat damage adds to the pressure.⁠[10, 25]

What’s helping

Protected islandsChristmas Island
Christmas Island holds one of the largest and least disturbed populations. The remote Chagos Islands, one of the biggest protected areas in the world, are another stronghold.⁠[6, 12, 10]
Protection works15 sites
On Zanzibar, scientists checked 15 sites over 7 years. Numbers were stable overall, and protected sites tended to do better.⁠[26]
Raising larvae27–30 °C
Labs are testing water temperature and day length to raise larvae, with the aim of restocking islands that have lost their crabs.⁠[16, 25]
What you can do
Watch them from a distance, never buy or eat them, and follow local rules about protected wildlife.⁠[1, 24]

Notable populations

Christmas Island (Australia)Vulnerable
One of the largest remaining populations, studied with GPS tags.⁠[6, 12]
Okinawa (Japan)Vulnerable
The northernmost population, where crabs are recognised by their carapace grooves.⁠[8]

Coconut crab quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

What is special about the coconut crab’s size?

Coconut crab field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

An omnivore, the Coconut crab eats coconuts, fruits, nuts, and even finds other dead animals.

Primary Foods

coconuts
fallen fruits
nuts
carrion
small animals
Foraging Method: Foraging

Ecological connections

Coconut PalmFood plant
Coconut flesh is one of its foods. Fallen fruit such as pandanus is also a main food.
Black RatSuspected predator of young
Suspected predator of young crabs, but not confirmed.
Wild BoarSuspected predator of young
May dig up and eat young crabs, but this is only suspected.

Safety

Danger 3/5 · Moderate

Never touch or pick up a coconut crab, because a big one can pinch very hard. Watch from a distance and tell an adult if one is near.

Traits

Collections

Mammals

Classification

Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Family: Coenobitidae
Genus: Birgus

Coconut crab sources

26 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Coconut crab?

Look for fins, arms, tentacles, shells and body symmetry. Underwater light shifts colors, so structure and markings usually matter more than shade. Sea Creature Identifier: upload a photo and compare the visible details.

How long is Coconut crab?

30-60 cm

How much does Coconut crab weigh?

up to 4 kg

How long does Coconut crab live?

up to 60 years

What does Coconut crab eat?

An omnivore, the Coconut crab eats coconuts, fruits, nuts, and even finds other dead animals.

Where is Coconut crab usually found?

Coastal areas

How does Coconut crab hunt?

Foraging

How many eggs does Coconut crab lay?

51000-138000

How big do coconut crabs get?

The biggest weigh up to 4 kg and have a leg span of about 1 m, which makes them the largest arthropods living on land. Males are bigger than females.

How strong is a coconut crab’s pinch?

The strongest pinch measured, among 29 wild crabs in Okinawa, was 1,765 N. Scientists estimate a 4 kg crab could pinch with about 3,300 N, more than any other crustacean measured.

Can coconut crabs really open coconuts?

Yes. They tear off the husk strip by strip from the end with the three eye-holes, then hammer one eye open with a claw. Coconuts are only part of their diet, though.

Are coconut crabs dangerous?

They are not aggressive, but a big one can pinch very hard. Never touch or pick one up; watch from a distance. Eating them can also be risky, because crabs that eat poisonous fruit can make people ill.

Can coconut crabs swim?

No. Only the larvae live in the sea. Adults breathe air with lungs and drown if they are kept under water.

How long do coconut crabs live?

Up to about 60 years. They grow slowly, become adults at about 5 years and reach full size only after 40–60 years.

Where do coconut crabs live?

On islands of the Indian and Pacific oceans, from Zanzibar and the Seychelles east to the Pitcairn Islands. Christmas Island has one of the largest populations.

Did coconut crabs eat Amelia Earhart?

Nobody knows, and there is no evidence that they did. One hypothesis links bones found on Nikumaroro atoll in 1940 to Earhart and suggests crabs scattered her remains, but experts disagree about the bones and a crab scientist calls the crab story a rumour.

Take the discovery with you