[KleineVampir]

I got some plants and mud from a local pond and have them in a large jug. As expected, there were a bunch of hitchhikers, including at least one leech, a bunch of pond snails, some daphnia, and some red worms that I'm pretty sure are Limnodrilus hoffmeisteri.

Of course, I'm keeping the jug separate from my other tanks. But I've had issues with substrate compaction in my planted tank (worm casings under pool filter sand) and, although I intend to get some MTS, I was wondering if adding the worms would help. Has anyone tried this? How did it go?

Sounds like a bad idea to me. Especially if you intend to keep inverts only, because inverts cannot get rid of worms to my knowledge. Only fish can. I'd say just get snails. I have no idea what you're talking about with substrate compaction and worm casings.