Well, I have to say the main conflict can quite easily be gleaned from the title if you look hard enough at it. It is an external conflict that pits man against nature in one of the scariest encounters between the two that I have ever read about. Leiningen is a farmer in Brazil with a plantation. He is facing a massive ant stampede that eats everything in its path and destroys all crops. Note how the Brazilian official describes the ant stampede in his efforts to try and get Leiningen to leave his farm to safety:
"They're not creatures you can fight - they're an elemental - an 'act of God'! Ten miles long, two miles wide - ants, nothing but ants! And every single one of them a fiend from hell; before you can pit three times they'll eat a full-grown buffalo to the bones."
The ants, then, are a very terrifying and powerful force of nature to content with and this story pits the intelligence and quick-thinking of one man against a natural opponent for survival.