I could only find articles related to them being poisonous to fish. It claims that it is the secretions of the worms. I can't imagine that they are poisonous since they are vermiform composters. But I don't feed hem myself.
Hmmm....I used to feed them to my box turtles before my red wigglers all died from too much heat . I still feed them when I dig one up and have not had a problem.
I've also used them as food for my turtles. Also without harm so that's why I was a little surprised to read that I guess maybe the toxin is targeted at the red wiggler's main predators in Europe the grass snake (Natrix) and true frogs (Rana) which are close relatives to the garter snakes and bull frogs.
Could it not be the worm but the way in which the worms were raised? Some worms are raised in the dropping of commercial chicken egg operations, all the manure antibiotics and such would be enough to... well kill a gartner snake or tad pole .
Hm, I hadn't heard that. I've feed them quite a bit, particularly when we had our hatchling. Both the hatchling and our adult ate them. (Our little guy has passed away from unknown causes, but our adult is doing quite well and still enjoys them.)