I can't find a reference to it anywhere, so let's just use Wordie to officially coin it. Those little bubbles need a name, and "wulm" has a nice collective ring to it--e.g., "That's a very active wulm you have going there, bard. Get the teabags ready."
I found this word, and the definition "the tiny bubbles moving up the sides of a pot just as it's about to boil" quite some time ago, but can find no documentation for it now. Sometimes I wonder if I made it up, or imagined the whole thing.