Why does a her­mit crab change its shell?

BBC Wildlife Magazine - - Our World - Polly Pullar

ALack­ing a pro­tec­tive ex­oskele­ton, a her­mit crab uses the va­cated shell of a mol­lusc as a tem­po­rary safe house, but must find a se­ries of big­ger homes as it grows. Find­ing a shell ex­actly the right size can prove dif­fi­cult, and can re­sult in bizarre house-swap chains. If a crab lo­cates one that’s not the right size, it will wait nearby un­til an­other crab look­ing for a new shell ar­rives. When that crab sheds its old home and takes the empty shell, our first crab moves in to that newly va­cated one, cast­ing off its own, which is then adopted by a smaller crab... and so on. The num­ber of hous­eswaps each crab un­der­takes in its life varies de­pend­ing on wa­ter tem­per­a­ture, habi­tat and species.

Her­mit crab: se­rial hous­eswap­per.

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