One morning, I came across an interesting sight: two hermit crabs living together, each with anemones attached to their shells. The larger of the two hermit crabs (hereinafter referred to as "Dai") had two large anemones attached to its shell. The other was a much smaller individual ("Sho") and only had one anemone.

The two approached each other, the atmosphere tense... Dai was struggling to attach an anemone he had peeled off the shell of another hermit crab that had died the previous day to his own shell (photo above). However, it wasn't working, perhaps because there wasn't enough space on his back. Sho watched him from nearby, looking rather envious (?).

About 30 minutes later, Dai seemed to give up and quickly walked away. Then Sho ran to the anemone and grabbed it tightly (photo below). When I went to check on it in the evening, the large anemone was swaying on top of Sho's shell, its tentacles spread out. I shouted in my heart, "You did it, Sho!"

The reason why striped hermit crabs desire sea anemones is that by attaching anemones, which fire venomous stingers from their nematocysts, to their shells, they reduce the chances of being attacked by predators. But when did striped hermit crabs learn that sea anemones could be used as weapons?

[Tokyo Sea Life Park Research Staff, Michi Amano]

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