The famous short story "Leiningen Versus the Ants" tells of a plantation owner who refuses to abandon his property in the face of an overwhelming approaching army of deadly ants. Instead, along with his faithful employees, he decides to stay and fight. He devises complex defenses consisting of moats filled with water and petrol and manages to hold the ants off for awhile. However, it ultimately seems that the ants will overrun the plantation and the defenders will die horrible deaths until Leiningen himself puts on a protective suit, charges through the swarms of ants, and, despite gruesome injuries, manages to reach the controls of a dam and flood the plantation.

The theme of this thrilling story is man versus nature. If we focus this and give it a little more detail, we could say that it is the triumph of the ingenuity and indomitable spirit of man against a formidable and relentless threat of nature. Man versus nature is a common theme in many classic tales. One example is Jack London's famous short story "To Build a Fire," in which a man hiking through Arctic wilderness struggles to survive in the midst of overwhelming cold and isolation. Another example is the short novel The Old Man and the Sea by Ernest Hemingway, in which an old man alone in a small boat in the Gulf Stream attempts to bring in a huge marlin.

The outcome of man versus nature struggles are not always the same. In "To Build a Fire," the man freezes to death. In The Old Man and the Sea, the ending is ambivalent, because the old man makes it back safely to shore, but the marlin he caught has been eaten by sharks. "Leiningen Versus the Ants," though, ends in triumph, as Leiningen survives his ordeal and saves the plantation and most of his workers.

One main theme of "Leiningen Versus the Ants" is persistence; Leiningen refuses to back down in the face of a natural destructive force, and although he suffers, he wins out in the end:

The sporting zest with which the excitement of the novel contest had inspired him the day before had now vanished; in its place was a cold and violent purpose. He would send these vermin back to the hell where they belonged, somehow, anyhow.
(Stephenson, "Leiningen Versus the Ants," classicshorts.com)

Leiningen believes that his human intellect is more powerful in potential than the irrational, mindless force of the ants. Despite some setbacks, Leiningen continues to fight and plan for new situations. At the start of the story, the District Commissioner tells him of the ants and their destructive abilities; Leiningen accepts his advice and chooses to act rather than flee. As the ants overwhelm his defenses through their sheer numbers, he finds more and better ways to attack them; finally, although he is badly wounded, he unleashes the river and wipes the ants out, showing his persistence in the face of seemingly unstoppable odds.

What is the main conflict in the short story "Leiningen versus the Ants"?

This is a good question, because, while the obvious answer is that the conflict is between man and nature, an equally correct answer would be to say that the conflict is between man and his own fear.

Leiningen's Brazilian plantation is directly in the path of a swarm of billions upon billions of ants, which devour everything they come across. The local governor urges Leiningen to evacuate the area, but Leiningen is confident in his ability to outwit the ants. He firmly believes "that intelligence, directed aright, invariably makes man the master of his fate," and he therefore refuses to flee in the face of danger. He has taken many precautions against the ants, digging ditches around his property and filling one with water, the other with gasoline. The Brazilian governor calls the ants "elemental," and Leiningen intends to fight this "element" with the other elements of water and fire.

When the ants arrive, Leiningen's precautions are put to the test, and while they hold, he glories in the triumph of his intelligence over this challenge from Nature. His confidence inspires his workers with equal sang-froid, and as long as everyone remains calm, they are able to match each move the ants make with another move that forestalls the ants' advance. Once Leiningen's precautions begin to fail, however, "even he could not free himself from a qualm of malaise." He wonders if "this brain [had] for once taken on more than it could manage[.]" Still, he is determined to keep his chin up and solider on.

On the first day, there is a terrific battle to keep the ants from crossing the first ditch, which is filled with water. When some ants get across and attack one of Leiningen's native workers, the man screams in fear and pain, and Leiningen realizes "that another such casualty, yes, perhaps this alone, might plunge his men into confusion and destroy their morale," and that if that happens, they're all as good as dead. He manages to calm the injured man by instructing him how to remove the ants, and order is temporarily restored.

On the second day, the ants build little leaf-rafts to sail across the water-ditch. For a time, Leiningen is able to slow their advance, but then the ants get over the water and begin devouring the workers, who scream in agony.

When Leiningen heard this, he knew the plantation was doomed. He wasted no time bemoaning the inevitable. For as long as there was the slightest chance of success, he had stood his ground, and now any further resistance was both useless and dangerous.

Still he does not succumb to fear. He sounds the signal to retreat behind the second ditch, the one filled with gasoline, and his workers follow him:

And there, drifting in twos and threes, Leiningen's men reached him. Most of them were obviously trying to preserve an air of calm and indifference, belied, however, by their restless glances and knitted brows. One could see their belief in a favorable outcome of the struggle was already considerably shaken.

Fear is gaining the upper hand over the men's determination to resist the ants' onslaught, and their desire to believe in Leiningen's invincibility. Nevertheless, they decide to stay with Leiningen at the plantation, rather than take rafts to the other side of the river.

On the third day, the ants try to cross the gasoline-ditch, which Leiningen sets on fire. The ants are thrown into disarray by the flames, but only temporarily, and when the fire burns itself out, the ants mass again to reattempt the crossing. Leiningen "felt for the first time since the arrival of the ants that his confidence was deserting him."

[...] the ants were coming on again as if nothing had happened. And meanwhile Leiningen had made a discovery that chilled him to the bone-petrol was no longer flowing into the ditch.

Leiningen remembers that he has two final cisterns of gasoline in an outhouse, and in desperation, he and his men hook these up and fill the ditch again.

It was obvious, however, that this last resource meant only the postponement of defeat and death. A few of the peons fell on their knees and began to pray; others, shrieking insanely, fired their revolvers at the black, advancing masses, as if they felt their despair was pitiful enough to sway fate itself to mercy.

The men lose their nerve completely and begin to run through the fire blockade in an attempt to reach the river and swim to the other side. For every man who crosses the ditch, the ants swarm him and devour him, but the men are now so terrified that they are past reason. In desperation, Leiningen hits on one final way to get rid of the ants: dam the river and flood the entire plantation.

His confidence in this plan is largely bravado, but his men rally round him anyway and help him to accomplish it. To reach the dam, Leiningen must wade through the sea of ants, so he douses himself in gasoline to prevent their bites, and, with supreme bravery, begins the long walk to the dam-mechanism. The ants swarm him anyway, and bite him ferociously, but he is absolutely determined to dam the river, and dam it he does. When the water begins to flood the plantation, he staggers back towards his men but is almost overcome with pain from the ants' poisonous bites. It is only horror at the thought of being "picked clean" by their jaws that keeps him from sinking to the ground and never rising again.

And in the end, his men save him, the plantation is flooded, the ants are destroyed, and Leiningen's confidence in the face of total disaster has saved him and most of his workers from death. Courage has triumphed over fear.

What is the main conflict in the short story "Leiningen versus the Ants"?

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.

What is the internal conflict in "Leiningen Versus the Ants?"

Although "Leiningen Versus the Ants" contains a strong external conflict -- Man vs. Nature -- it has little obvious internal conflict; from the beginning of the story, Leiningen is determined to fight the ants, and the events that follow show his will to continue. Leiningen does not vary from his original purpose, but does exhibit a moment of self-doubt as the ants threaten to overcome his defense:

...he felt for the first time since the arrival of the ants that his confidence was deserting him. His skin began to creep; he loosened his collar. Once the devils were over the trench there wasn't a chance in hell for him and his men. God, what a prospect, to be eaten alive like that!
(Stephenson, "Leiningen Versus the Ants," classicshorts.com)

The fear of being eaten alive by the ants gives Leiningen his internal conflict; is it worth continuing to fight, knowing that he might lose and be consumed in such a horrible fashion? However, as he fights the ants, Leiningen comes to the conclusion that he will not give up and run, but will fight until his last breath; he feels that he owes that to both his men, who believe in him and fight for him, and for his own personal pride. In this manner, he resolves his internal conflict.