Zoo Med Excavator Clay Burrowing Substrate Since 1977 Zoo Med has been creating high quality exotic pet foods products and habitats for reptiles amphibians fish and other exotic pets. Zoo Med Zoo Excavator Clay Burrowing Substrate is a clay substrate that can be formed to your liking while still allowing reptiles to dig tunnels and burrow as they do in nature. Mold and create multi-level terraces and burrows in your reptiles terrarium.