Flesh-Eating Slugs?????? Isn't that just a misunderstanding?

It's something I've wondered about for some time...I have found various references form different sites that there are "flesh eating slugs" in the Potter verse, most likely based on Hagrid saying that he bought "flesh eating slug repellent" to protect the cabbage in his garden in CoS. A lot of people seem to take this as that he bought something to repel flesh eating slugs. But that doesn't make much sense to me, because if the slugs are flesh eating, why would there be a need to protect the cabbage from them? Can't it be that the repellent is flesh eating in order to thoroughly destroy common slugs? o do I get the rules of the English language wrong?