Fire Breathing Weapon: Plenty of ’em, up to and including flame tanks.  For two reasons: one, fire is scary, and since there are very few species indeed willing to charge directly into a wall, cloud, or ocean of fire, they make excellent area-denial weapons against light infantry.  Without having to kill anyone not led by General Stupid, even.  And two, they’re great against nanoweapons and other swarms in general, because it doesn’t take all that much fire to make them exceed their heat budget and stop working.  And since nanowarfare is quite popular, such a convenient way of dealing with it is most useful.