The coconut crab, or “robber crab” (Birgus latro), is the largest terrestrial arthropod in the world, with individuals weighing up to four kg (about 9 pounds). They have a wide range:
But because of their size and the fact that they’re tasty, they’ve been largely driven extinct by humans on populated islands. Here’s how big they are:
They come in different colors, often red or blue. Here’s a beautiful blue one:
Two facts about these species. First, they’re fairly close relatives of the hermit crab, and in fact are descended from hermit crabs that occupied shells throughout their lives. But this species is sufficiently large as to have few predators besides humans, and so only the very young and small coconut crabs live in shells (sometimes bits of coconut shells). They’re also completely terrestrial, and will die if put in salt water.
You can see the hermit-crab ancestry in the reduced and curled abdomen…
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