In light of my own predicament with my betta Train, I feel compelled to warn my fellow betta owners about live black worms.
Last week, I bought what I was told were live bloodworms and fed them to Train. That same night, I noticed he had a very large blockage that was literally making his belly pointed. A week in 3 tsps of epsom salt per gallon and IAL has done nothing to move this mass out of his system. He will most likely need to be euthanized.
Further research on google led me to discover that the worms I was sold were not bloodworms but were in fact black worms. And that's where everything went wrong for poor Train.
Here is what The Betta Handbook by Robert J Goldstein has to say:
"Bettas may engorge on black worms, resulting in gastric distress and sometimes death. Many aquarists cut them into pieces with a razor blade before feeding them to bettas. Black worms that survive partial ingestion can tear the stomachs of small fish, killing them." (pg 93, Goldstein)
If you purchase live worms, do double-check to make sure they are bloodworms. If you intend to feed black worms to your bettas, feed only one or two at the very most and probably do as the book suggests, cutting them into pieces.
I don't want anyone else to have to go through what Train and I are going through. Be very careful when purchasing and feeding live worms.