I have a small garden that has plenty of worms for growing my chilis and for fishing. Historically, they weren't there in quantity and size, but a couple of winters ago I worked in a bag of alfalfa pellets. I worked them in to about 12" deep. By Mid spring, there were many worms and they were fat things and I could tell there had been a lot of reproduction too. The alfalfa seemed to have made a big difference for them. If you did something similar, the enriched bed should attract native worms which would thrive in the enriched soil. If just for the purpose of growing worms for fishing, I think just spreading some on a patch and covering the patch with a good mulch like straw would work just as good or better provided you have worms already in the soil. Not a how to but they should do well if there is plenty of food for them. Didn't ask where you are from but armadillos and skunks will dig in them if located in the country where these would be present. A mulch like tin or plywood sheeting would help to keep them out.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers