T-Rex Hermit Crab Substrate - Terra Mix Calci-Sand & Natural Shell MixHermit Crab TerraMix is an ideal substrate for hermit crabs, it includes white Calci Sand and natural shells which are packaged separately. It allows you to create your own natural environment for your hermit crab with the 2 substrates provided. You can either use one of the suggested methods on the bag (mix, layer, design, or divide), or use your own creativity to create a natural environment in your hermit crabs habitat.