there are quite a few on-line sources of redworms for composting purposes-- generally, the cost is about 30 dollars for a pound of the buggers--
the species of worms one would dig up are not happy if placed in 'confinement' They also do not find close quarters with other worms to be beneficial unless they are getting ready to overwinter or breed. But, that does not mean they cannot explode their population numbers under some rabbit cages... You can pick the retgular earthworms a lot easir by placing cardboard sheets on the ground in the evening, then in the morning, pick it up, and be real quick snatching up your prey!!