Ant-stralia's army ants are quite difficult on insane difficulty, but they should definitely be simpler to deal with than e.g. the samurai ants of Eur-ant-ia, as long as you're being aggressive enough. South Ant-merica can also seem easier if you manage to pit our enemies against each other and strike in the confusion.
So how hard a continent is will often depend on what strategies you're using and which difficulty you're playing on.
But thanks for joining the conquest, and long live the Ant-peror Queen.