you should ask @Vhuang168 . Vincent did a group buy about a year ago for the black worms, (not to be confused with tubifex worms) .
Maybe Vince will chime in and share his source with you.
I will have to admit, my fish "loved" the black worms.
Just feed. I've been told that sometimes a Copperband will eat blackworms. So far, I've tried frozen mysis, live clams, shredded shrimp, NLS pellets, Hikari marine angel food, with no luck.