I actually wrote an article about bristle worms. It's in the articles section of this site. Bristleworm and fireworm are interchangeable umbrella terms for polychaete worms.
That being said, as Beengirl stated, most polychaete worms are beneficial and no cause for concern. In fact, I would go so far as to say that an absence of bristle worms would be a serious problem. They are the best cleaners you'll ever find!
The "ants" you described sound like copepods. Again, a good thing. Stomatella snails are efficient little herbivores that will breed readily in our tanks. In terms of hitch hikers and 'accidental' life in our tanks, very few are cause for concern. Mantis shrimp, red bugs (if you keep sps
), majano, and aiptasia anemone, for example. But for the most part, finding new life forms is indication of healthy biodiversity.
I totally understand how you feel. Even now, I stare at my tank up close to watch the tiny life forms. Mysid shrimp, copepods, amphipods, worms, stomatella, chitons, limpets, etc. It is really amazing.