As a youngster fishing the Grand River in NC Mo., we used to dig green river worms for bait. We called them that because they were light green and you only found them in riverbanks. The Grand cuts thru fertile farming ground and is lined by steep soil banks. If you could find a layer of rotting leaves buried in the bank, there they were. About halfway in size between a red wiggler and a nightcrawler, and covered in a strong-smelling slime that you couldn't wash off your hands for a couple days. The best way to describe the smell here is just to say it wasn't anything you wanted your girlfriend to get a whiff of on you, but when you thought no one was around, you might get caught smelling your fingers...
When you could get them, they were the fish-catchingest bait I've ever found by an order of magnitude. Every kind of fish in the river ate them with gusto. One seldom sat more than a minute, and I don't think I ever had to take one off a hook.
I've searched the web, and only found a few references on a couple catfish forums. I assume they probably have another name. They are somewhat similar in appearance to what are called milk worms, but those lack the extreme slime and smell. Has anyone here ever encountered them?