i would only bother with worms if your working with a good organic amended grow, in large pots, or your wasting your time.
but if you want to know a secret to more worms, get some white/brown bread with some marmite on it/vegimite, yeast extract. it works like an asphrodiziac and you get baby worms, dont over do it. just a slice in a worm bin will do it.
your best off keeping worms in a bin and out your grow