Cocopeat

“If you are making a soil or naturalistic setup for your ants, you can use cocopeat instead. It has been widely used in the exotic pet trades as substrate for all invertebrates, such as tarantulas, scorpions, isopods, frogs, etc. It doesn’t have any contaminations in it that could harm your ants. It is the base substrate for all types of substrate mix. You can mix it with sand, orchid bark, and sphagnum moss to make tropical rainforest substrate. You can also use this in the outworld as the flooring decor.”
– DavFoo