Discover Hermit Crab Essential, pure worm castings designed specifically for your hermit crab's crabitat, Worm Castings are also a great fertilizer for your garden.  Castings are an essential in a hermit crab crabitat. This is something they must have in their tanks at all times. Our castings are pure and have no fillers are ever added. Hand sifted by the garden and worm lady herself.