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Coconut crabs (Birgus latro) are giant terrestrial hermit crabs found on islands across the Indian and Pacific oceans. Exceptional individuals can exceed 4 kilograms and measure about a metre across, but most are smaller. Young crabs use portable shells; mature crabs develop a hardened abdomen and live on land.
Despite their name, coconuts are not the main item in their diet: coconut crabs are omnivores that eat fruit, seeds, nuts, carrion, and other animal material. Their life cycle still depends on the sea, where their larvae develop before young crabs settle near shore and move onto land. The 2022 conservation review reports that the species is classified as Vulnerable; older sources calling it Data Deficient are out of date.
17 coconut crab facts
1. It is one of the largest land-dwelling arthropods
Exceptional coconut crabs can weigh more than 4 kilograms and span up to about one metre from leg to leg, according to Parks Australia and the Western Australian Museum. These are upper-end measurements, not typical adult size; most coconut crabs are considerably smaller.
That span is not the animal’s body length. It describes the distance across its extended legs.
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2. It is the only living species in its genus
The coconut crab’s scientific name is Birgus latro. It belongs to the hermit-crab group and is commonly called a robber crab. Its distinctive size and adult lifestyle set it apart from the familiar small hermit crabs that continue to carry shells.
3. Young coconut crabs use shells
Young coconut crabs protect their vulnerable abdomens by carrying empty shells. As they mature, they develop a hardened abdomen and stop carrying a portable shell. Parks Australia describes this shift from shell-carrying juvenile to terrestrial adult.
4. Adults live on land, but their larvae develop in the sea
Adult and juvenile coconut crabs are terrestrial, but the species depends on the sea during reproduction. After hatching, larvae develop in the water; late-stage larvae settle in shallow water, acquire mollusc shells, and then move onto land.
The 2022 conservation review reports a planktonic larval phase of about four to six weeks, depending on temperature. Ocean currents affect larval dispersal and whether young crabs reach suitable islands.
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5. It needs more than coconut palms
Coconut crabs are island animals, but a coconut grove alone does not describe their habitat needs. They use terrestrial habitat for shelter and foraging, while their life cycle also requires suitable shoreline and marine conditions for larval development and recruitment.
6. Its range spans Indian and Pacific islands
The 2022 conservation review describes a broad island range extending from the east coast of Africa through Indonesia, Micronesia, Melanesia, and Polynesia as far as Pitcairn Island. Occurrences on larger inhabited continental landmasses are rare. A broad range on a map does not mean the species is present or secure on every island.
7. Its distribution is shaped by ocean currents
Because larvae spend weeks in the sea, currents influence how they disperse and whether they return to suitable islands. The species’ land and marine stages are connected: protecting adult habitat alone may not safeguard the full life cycle.
8. It is mainly nocturnal, with local variation
On Christmas Island, coconut crabs usually shelter during the day and emerge at night or on overcast days, according to Parks Australia. Daytime activity can also occur when conditions are humid, as the Western Australian Museum notes. Their activity is therefore not governed by an absolute day-or-night rule.
9. It is adapted to life out of water
Coconut crabs spend their juvenile and adult stages on land, unlike many crabs that remain aquatic. Their terrestrial life does not make them independent of the ocean, however: larvae develop at sea before settling and moving onto land.
10. Coconuts are not its main food
Coconut crabs are omnivores. Their food can include fruits, seeds, nuts, fallen-tree pith, carrion, and other animals. Parks Australia describes forest-floor foraging and scavenging on Christmas Island; the Western Australian Museum also describes an omnivorous diet.
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The Western Australian Museum cautions that, although coconut crabs are famous for opening coconuts, coconuts are not the main item in their diet.
11. It may eat other animals
Coconut crabs do not rely only on plant food or carrion. The researched accounts describe occasional predation on other animals, including turtle hatchlings on Christmas Island, as well as scavenging. What they eat varies with local food availability.
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The Western Australian Museum reports that coconut crabs can climb trees up to about 10 metres. Climbing is part of the reason for names such as palm thief and robber crab, though it should not be taken to mean every crab climbs to that height.
13. Opening a coconut can take several days
Opening a coconut is an effortful behavior, not evidence that coconuts dominate the crab’s diet. The Western Australian Museum reports that the process can take several days and often involves several crabs.
14. Young crabs must move from the sea onto land
Late-stage larvae settle in shallow water, acquire mollusc shells, and then move onto land. That transition connects marine, shoreline, and terrestrial habitat. The 2022 conservation review describes this sea-to-land recruitment as part of the species’ life cycle.
15. It can live for more than 50 years
Parks Australia says coconut crabs can live for more than 50 years. Their long lives and slow population turnover mean that heavy harvesting can put pressure on populations, particularly where large adults are removed.
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The 2022 conservation review reports that the coconut crab’s assessment changed from Data Deficient to Vulnerable as information about its range, habitat, population sizes and trends, and threats improved. Do not rely on older sources that still use the Data Deficient label as the current global status.
17. Human pressures affect populations across its range
The conservation review describes pressure from human populations and uneven protection across the species’ range. Protecting coconut crabs means considering both their terrestrial habitat and the marine and shoreline stages needed for recruitment, alongside local conservation measures.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Frequently asked questions
How big do coconut crabs get?
Exceptional individuals can weigh more than 4 kilograms and measure up to about a metre across from leg to leg, according to Parks Australia and the Western Australian Museum. Those are maximum-size descriptions, not typical measurements.
What do coconut crabs eat?
They are omnivores. Their food includes fruits, seeds, nuts, fallen-tree pith, carrion, and other animals. Coconuts are not the main item in their diet.
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Do coconut crabs really crack coconuts?
Yes. The Western Australian Museum reports that opening a coconut can take several days and often involves several crabs. This notable behavior does not make coconuts their main food.
Where do coconut crabs live?
They live on islands across the Indian and Pacific oceans, with the 2022 conservation review describing a range from the east coast of Africa through the Indo-Pacific to Pitcairn Island. Their larvae develop in the sea before young crabs settle and move onto land.
Are coconut crabs endangered?
The 2022 conservation review reports the species as Vulnerable. Older sources that call it Data Deficient do not reflect that updated assessment.
Are coconut crabs hermit crabs?
Yes. Young coconut crabs carry shells, as hermit crabs do. As they mature, their abdomen hardens and they no longer carry a portable shell.
The Bottom Line
Coconut crabs are giant terrestrial hermit crabs with a life cycle that links the sea to island shorelines and land. Their remarkable size and ability to open coconuts make them memorable, but coconuts are not their main food. The 2022 conservation review classifies the species as Vulnerable, underscoring the importance of protecting habitat and the full sea-to-land life cycle.
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