Terrariums

I've been thinking about making bio-active terrariums for a while (well, not just terrariums but just jars of things to put in my room for fun like a jar brains made of clay you'd usually find in an souvenir shop or smth). I just thought it be fun, it could also help with my fear of bug and my hallucinations surrounded with them. 

If anyone has any tips, they would be most appreciated!
But all in all, I just thought it was a cute idea :P