Animal · United Kingdom, Ireland, Norway
Hermit crab
Paguroidea — the name this animal has in the language scientists everywhere share.
A hermit crab has a soft, curled back end, so it moves into the empty shell of a dead sea snail and carries that borrowed house everywhere. When it grows too big for it, the crab goes house hunting and swaps into a roomier one.
Picture credit: Satheesha J. (CC BY-SA 4.0) · NOAA (Public domain) · Rene Cortin (CC BY-SA 4.0) · Wikimedia Commons
Where does the hermit crab live?
Home: in rock pools and on sandy seabeds along Atlantic coasts.
In the wild it lives in these countries: the United Kingdom, Ireland, Norway, Iceland, the Netherlands, France, Spain, Portugal.
The short profile
Fully grown: shell up to 3.5 cm, body about 10 cm. It weighs about 0.03 kilograms. On the menu: both plants and meat.
The story behind it
Only the front half of a hermit crab wears armour. The back half is soft and twisted, exactly the shape of the spiral inside a snail shell, so an empty shell is armour and bedroom in one. The crab tries a new home the way you try shoes: it turns the shell around, feels inside with its legs and slips in backwards. On some shores a whole line of crabs forms behind one big empty shell, sorted from largest to smallest. The moment the biggest one moves in, every crab behind it grabs the shell in front, and a dozen animals are rehoused within seconds. Researchers call this a vacancy chain and have watched it closely on Long Island and on Caribbean beaches.
Find it on the globe
Hermit crab is there as a tiny animated figure that breathes and looks around. From far away the planet is only a blue ball; detail arrives as you zoom in, and this one appears once you are close enough. Open it on the globe.
It sits at its real coordinates, not near them — the same numbers listed in the facts above. Switch off the layer for this kind of place and it disappears again; the buttons for that are down the right-hand edge.
Questions children ask
Is the shell part of the hermit crab?
No. It is a second-hand house from a dead sea snail, and the crab's own armour covers only its front half.
Where do hermit crabs live?
Why do hermit crabs queue up?
When a big empty shell shows up, they line up by size and swap in order, so one shell can rehouse a whole row of crabs.
Where these numbers come from
Every figure on this page was checked against public reference sources before publication. Where sources genuinely disagree, the text says so.
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