We are not talking of the same worm, the worm that you mean it is called here gloss worm and is suitable for feeding. It probably belongs to the genus of earthworms, I myself have not yet caught him, at least not consciously, but now and then I have seen in my aquariums one. Earthworms are an excellent food, but since they are usually slightly larger may make you more likely to feed on large fish. The way of life of Glanzwürmen similar to the Tubifex, so nice if you have a food source.