"Leiningen Versus the Ants," by Carl Stephenson, is available to read for free on the website linked below. Here is a short summary.
Leiningen, a plantation owner in South America, is informed that a wave of fierce army ants is moving towards his plantation. Rather than flee and leave his years of hard work to be destroyed, Leiningen resolves to stay and fight the ants; his men, who respect him for his success, remain with him. He fights the ants using moats of water and gasoline, steers them to expendable fields, and he and his men crush the ants that breach their lines. However, the sheer numbers of the ants are enough to drive him back, and they begin to overwhelm his defenses. As a last resort, Leiningen wraps himself in gasoline-soaked cloth and runs for the river dam; he is badly bitten but manages to block the river, flooding the plantation and destroying the ants along with that year's crops. As the story ends, Leiningen wakes from his trauma-induced sleep and asks about the ants; he has won, and sleeps to recover.