Red Feeding Worms

I saw a couple of these small red worms sorta stuck together in a ball. They were kept in small tanks and pails and the water was pumped with air using an air stone. All of them were moving.
LFS said they were fish food.

I have seen frozen blood worms but I haven't seen them alive. Are these live blood worms that I saw?

I bought some notheless and fed them to my pl*cs. How do I keep the rest of these critters alive for a longer perid of time? Just aeraton with an airstone? How often do I change water for them worms?

Thanks,
Mike D.