Another one is mother nature. When she wants us gone there isn't a whole lot we can do about it. Plus if we keep it up with killing things like the bees, we only hasten her wrath upon us.
It could be anything from volcanoes to earthquakes to tidal waves. No matter where you are in the world there is a way for mother nature to get you. Do you think there will ever come a time mother nature strikes back in force?