Bristleworms, Fire Bristleworm is one species, are not necessarily bad for your tank. In fact in small numbers will benefit your tank by serving as detritavores, helping to keep your tank clean. They become a problem if they start appearing in large numbers or if they start to chow on things you don't want them to. For now I would leave them alone. In time your tank will strike up a balance with the worms and rest of the ecosystem.
BTW, Fire Bristleworms can cause a nasty sting, so use gloves when messing around in your tank.
