I can snip the heads off before feeding, they still wriggle around heaps!
It now sounds like it is what we call bloodworms. It has many times the fish attractant value when fishing for small saltwater fish species here in the mid Atlantic USA. Like I said, we pay $10 - $12 dollars for a dozen of these worms vs. $2 - $4 for large earthworm (Night Crawlers).
If this is the case, I would never go back to earth worm/ night crawler if I could even get Bloodworms at the same price as E.W/N.C's! If they were less expensive, it would be a no brainer.
I have heard of these worms causing serious blood from a fisherman's finger when it is handled improperly. It might be a good idea to lop off the head before feeding similiar to removal of crayfish claws prior to the use as feeders.