Sequential shell swaps in hermit crabs

Here’s another Attenborough video featuring the lifelong attempts of hermit crabs to find shells that fit them as they grow. A hermit crab without a shell is a pathetic thing (see several at 2:39), easily taken by predators or cooked by the sun. Here’s a stunning behavior in which a line of crabs forms in order of size, with the aim of each one swapping up to a bigger shell within a matter of minutes. Or course, the biggest crab needs an empty bigger shell to move into, which apparently is the case here. The picture of the lineup at 1:32 is fantastic.

The video comes from “Life Story,” part of the great BBC Earth series.


  1. ThyroidPlanet
    Posted January 23, 2020 at 3:06 pm | Permalink


  2. Posted January 23, 2020 at 3:16 pm | Permalink

    The music is dippy, but those crabs are adorable! I had no idea that they exhibit this behavior — I would have thought there were plenty of shells of all sizes available.

  3. Stephen
    Posted January 23, 2020 at 3:27 pm | Permalink

    I wonder why did natural selection favor this instead of having their own shell grown like lobster or crabs?

    • Posted January 23, 2020 at 3:42 pm | Permalink

      Why go to the expense of growing your own shell when there are perfectly good shells littering the sea floor? Put your resources into reproduction. Just a guess.

      • Peter N
        Posted January 23, 2020 at 3:57 pm | Permalink

        …after all, that’s our strategy, more or less!

        • rickflick
          Posted January 23, 2020 at 5:00 pm | Permalink

          I now live in a house bigger than the previous one, and, true, I have one offspring to show for it.

  4. Posted January 23, 2020 at 3:46 pm | Permalink

    Great video!

  5. JezGrove
    Posted January 23, 2020 at 4:22 pm | Permalink

    Slightly off-topic, but David Attenborough recently came top in an opinion poll of who Brits were asked who their dream prime minister would be:

  6. Posted January 23, 2020 at 6:22 pm | Permalink

    Hermit crab inequality apparently mirrors our own. Curious.

  7. Muffy Ferro
    Posted January 23, 2020 at 6:34 pm | Permalink

    So wonderful to see that cooperative behavior! Funny little creatures 🙂

  8. Posted January 24, 2020 at 12:20 am | Permalink

    Very nice.

  9. Posted January 24, 2020 at 5:53 am | Permalink

    Don’t you just hate it when you’ve booked the removals, and the chain collapses at the last minute.

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