i pick up and take home any new species of moss i find when i'm out walking around in my yard/woods, or when i'm out somewhere (i.e. looking for land to buy), and put them in my bog garden to see how well they grow. not a terrarium, but something neat to collect :). i'm going to try to place some rocks sometime soon and grow more of those types which cling to rocks

Terrariums are generally not the easiest way to grow carnivorous plants anyways, mostly due to fungus. Live sphagnum also tends to overgrow small carnivorous plants, so needs to be kept clipped back if used. I tend not to rely on live moss, but I would not mind trying some on my larger plants someday.