I normally don't add any soil to a worm bin. Never know what might hitch a ride. If you want to "rush" them (sorry, armoured), get some aged manure. I am far from horses and now a days I can't find pure manure sold at Garden Centres. What's in the bag is already mix with stuff, ready to use for the garden. I believe it said it's mix with compost but what I found were lots of wood pieces. I screened it with a 1/4" mesh and added the fine stuff to the bin. Make sure there are no chemicals mixed into the bag.

Failing that, if there's a fresh juice shop near your home. These places mostly sell wheat grass juice also. Ask them for the spent wheat grass mat and you can use that rather than just soil. It should be safe to use because it's supposed to be organic.

Worms love to hide in there and leave lots of cocoons in the process.