The incredible size of the coconut or robber crab (Birgus latro) can be attributed to its early life, alone on remote islands.
With no humans or big mammals to share their cut-off domain they thrived, killing and scavenging food and helping themselves to the title of the largest land crab in the world.
Coconut crabs are now known to grow up to 3ft (1m) long and weigh as much as a large human baby, but their extreme size has left the females of the species with a dangerous problem.
Their eggs have to be hatched in the sea, but coconut crabs are non-swimmers and can quickly drown.
To get around this reproductive quandary, females have to navigate the shore at high tide and carefully release their young into the warm water as they hatch. The larvae are able to breathe underwater until they leave the ocean as young crabs.
Find out about more animals that have survived on isolated islands in the second episode of Japan: Earth's Enchanted Islands on Monday 15th June at 21:00 BST on BBC Two.
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