Advertisement I have a 55 gallon enclosure with 10 inches (deep) of substrate. The substrate is a mixture of top soil, some potting soil, some sand, sphagnum moss and rocks rounding out the mix. Quite a few deep rooted plants are in the enclosure, so I am thinking that I need more insects that can burrow to keep everything going. I currently have a dozen red worms, half a dozen millipedes, twenty isopods. With so much soil, I'm thinking that more isopods might be needed, but I don't want to overstock (if that is even possible). Or maybe I should be looking for something other than isopods???? I know that spring-tails are needed, and as much as I want to get them locally, I may have to break down and just order them online.