I talked to people on a yahoo group who cultured their own blackworms. They used a bucket that was like 3/5ths full with a bottom lining of brown paper in room temp water. They had a sponge filter in the bucket, and fed them algae wafers and pellets daily. While the blackworms did multiply, it wasn't like population doubling in a week.
I tried this once, but forgot to use a cycled sponge filter and it crashed and my house smelled awful.