Head to head
Coconut Crab vs Hermit Crab
The coconut crab and the hermit crab are the same kind of animal at different stages of an evolutionary journey. Both belong to the hermit crab group, and a young coconut crab lives exactly like any other hermit crab, carrying a borrowed snail shell on its soft rear end. The difference is what happens next: the coconut crab grows out of the habit entirely, hardening its own abdomen, and becomes the largest land-living arthropod on Earth.
| Coconut Crab | Hermit Crab | |
|---|---|---|
| Relationship | A hermit crab that stopped using shells as an adult | The broader group of about 800 species |
| Size | Leg span up to about 1 m, weight up to 4 kg | Mostly small, from a few mm to hand-sized |
| Shell as an adult | None; carries a hardened abdomen | Always; a borrowed snail shell |
| Habitat | Land only, on tropical islands; drowns in the sea | Mostly marine; some land species |
| Breathing | Air, via a modified lung-like organ | Gills; land species use modified gill chambers |
| Superpower | The strongest pinch of any animal for its size | Shell swapping and, as a group, vacancy chains |
| Diet | Fruit, nuts, carrion, and coconuts | Scavenges detritus, algae, and small prey |
| Conservation | Vulnerable; slow-growing and eaten by people | Most species not assessed or not threatened |
Coconut Crab vs Hermit Crab: common questions
Is a coconut crab a hermit crab?
Yes. The coconut crab, Birgus latro, belongs to the family Coenobitidae, the land hermit crabs, and it is the only member of its genus. Juvenile coconut crabs behave like any hermit crab, protecting a soft abdomen inside a borrowed shell, and sometimes using broken coconut shells when snail shells run short. As the crab matures it hardens the skin of its abdomen into a curled, armoured tail plate, stops using shells, and continues growing far beyond the size any shell could accommodate. So it is a hermit crab that has evolved its way out of the defining hermit crab behaviour.
How strong is a coconut crab's pinch?
Extremely strong. A study measuring the pinching force of coconut crabs found that a large individual can generate over 3,000 newtons with its major claw, which is comparable to the bite force of a lion and is the strongest known for any animal relative to body mass. The claws are used to husk and crack open coconuts, a job that can take a crab several days, and to defend against rivals. A pinch from a big coconut crab can break bones, and the standard advice if one grabs you is to stay still or, in local knowledge, to tickle the soft underside of its body until it lets go.
Can a coconut crab swim?
No, and this is a key difference from most of its relatives. Adult coconut crabs have lost the ability to breathe underwater; they have an organ called a branchiostegal lung that works only in air, and an adult held under the sea will drown within hours. They live entirely on land, often well inland and up trees, and only return to the shoreline to release their eggs into the water, where the larvae drift and develop before crawling ashore. Ordinary marine hermit crabs, by contrast, are fully aquatic.