Springtail update: I regret to announce that though my jar populations are thriving, a horrible worm* is preying on my attempts to establish a terrarium population. >:(
I'd originally decided not to get isopods for this build because they might nibble on the roots of my plants if they don't have enough food, but word is they're great population control for flatworms so it looks like I'll be getting some little rolly dudes after all.
*Rhyncodemus sylvaticus, probably