Compost-ology Worm
Harvesting Worms - Migration

When the bedding has diminished to the extent that it is not deep enough to make a hole to bury fresh garbage, it is time to add fresh bedding. Prepare about one-half the orginal quantity of fresh bedding. Pull all of the vermicompost in your bin over to one side and add the new bedding to the empty side. Bury your garbage in the new bedding and let the worms find their way to it.

Every two or three months, you can remove the vermicompost, replace it with more fresh bedding and keep going back and forth from one side to the other in this manner. The vermicompost you remove will still have some worms in it, but enough should have migrated to the new bedding so that you needn't worry about harvesting the few that remain.