I was hoping that the ants were somehow milling food, perhaps using small rocks and sand (or a mutualistic relationship) over time to break it down. If a valuable food source was locked up and could only be accessed this way, I can certainly imagine an ant colony evolving to mill it somehow. They already farm fungus and aphids. I predict a new kind of ant mill will be discovered!
Given that we are busy killing off all the vertebrates, perhaps in a few million years their technology will be as advanced as ours. Then the ant archeologists will wonder if these strange giant quadrupedal creatures could have been intelligent, perhaps even enough to have a civilization.
