The design of your worm bin is important. I strongly recommend that you use a modular design to save the messy task of separating worms from their casts.

UK one-stop shop for Worm composters & bins

As more food is added to a module the worms work their way up turning the food into worm casts. When full, a new module is added, and the worms move up into it. The top module with food always contains the vast majority of the worms.

Modular worm bin factory - U.S.A. The big advantage to the modular designs like the 'Worm Chalet' on this link is that the worm casts in the lower module can be removed without any need for separating out worms. Otherwise separating worms is necessary to save you buying new worms every time the bin is full. Remember, worms bred to do composting are specialists at eating, not burrowing as earthworms do.

I use the modular designed Can-O-Worms bin and find it successful. I have also used a single compartment bin and discovered its disadvantages.

Although there are 2 methods for separating worms from a pile of casts these are a bit messy for a busy gardener and only practical when you farm the worms using worm breeding boxes.

So avoid bins made of a single compartment and choose bins that have a modular construction. Note that both these types usually have a lower compartment with a tap to collect the nutrient rich liquid that filters through.

The composters are usually supplied with worms, bedding, and food.