Crabs are surprisingly noisy once you put a contact mic near them. The shell taps against rock, the claws click on themselves the way castanets do, and the legs make that quick skitter across wet sand that nature documentaries love to push high in the mix.
You will find 8 crab clip here, covering scuttling foley, hermit crab shell shuffles, claw snaps, and a few underwater bubble passes for tide-pool ambience. Animators reach for them when a CG crab needs weight, and game audio teams use them under beach levels to thicken the ground layer. Free MP3 download, no signup needed.