"Saki came to the short story as a satirist," argues one literary critic, "and never averted his eye from the darker side of human nature, a place where not only social ineptness, pomposity, and foolishness are rooted but criminality as well." What human vices or follies does Saki ridicule in "The Interlopers"?
Saki (H.H. Munro) is a satirist and his works often demonstrate ironies which highlight, as you say, the "vices and follies" found in human nature. In "The Interlopers," the two main characters are Georg Znaeym and Ulrich von Gradwitz. They are the third generation participants in a family feud, and it is their unwillingness to let go of the past and their greed which get them killed.
The two families have been feuding for three generations over a "stupid strip of forest," but these men have gone even further. The feud is now a personal one which Saki describes this way:
[I]f there was a man in the world whom [Ulrich] detested and wished ill to it was Georg Znaeym, the inheritor of the quarrel and the tireless game-snatcher and raider of the disputed border-forest.
What a ridiculous thing for these men to be ready to kill today because of something which their grandfathers did decades earlier.
Even worse, their community has bought into this feud, though it does not affect them personally. Once the two men decide to settle their differences, they know the townspeople will be shocked and surprised that the feud has ended. Perhaps they would even have been disappointed, as human nature rather enjoys a good fight and taking sides in it.
The strongest commentary Saki makes is about the consequence of greed, a universal flaw in human nature. Because these two men have been feuding over ownership of a piece of land which has already been established by the men themselves as being worthless, they are here on this night to hunt and kill. Instead, they become the victims of their own greed. Trapped under a tree trunk in a storm, the men are at the mercy of nature; in this case, nature (in the form of wolves) is merciless.
Both holding on to anger (taking up another person's offenses) and being greedy (coveting) are flaws which Saki addresses with satire in this story.