Aliens (The Screwfly Solution)

In Alice Sheldon's disturbing short story "The Screwfly Solution", men all over the world suddenly become misogynic and murder countless women and girls in the process. Ultimately, the plot is unraveled to be the work of bizarre Aliens.

Short Story
The titular method is a scientific procedure to exterminate screwflies by causing them to become murderously aggressive towards the females of the species when aroused. It's brought up to a far more disturbing level when men all over the world begin acting in a similar manner. The main protagonist Anne tries to save her daughter during the onslaught but loses her to her affected husband. Towards the conclusion of the story, it is revealed that the onslaught was prompted by the arrival of aliens that engaged the same kind of procedure on the human race so they could have the planet. The end of the story implies that they succeed with their goal.

Masters of Horror
Their role in the Masters of Horror adaptation of the story is relatively the same, although they gain a more detailed appearance. Following the death of her daughter, Anne is forced to flee when two hunters discover she is a woman and give chase. In the woods, Anne comes across the light-like aliens that have been prompting the self-destructive tendencies of the human race. The hunters attempt to kill one that effortlessly kills the hunters with a beam attack. Like in the story, their efforts lead to the extinction of the human race.

Motive
In the original short story, they were more or less the typical conquering alien race that met this goal by corrupting the human male sexual drive and channeling it into aggression and murder. They are successful in their efforts and presumably take over the Earth following the death of humanity.

In the Masters of Horror adaptation however, there is a peculiar environmental motive given/theorized as the aliens' reason for enacting the extermination of the human race. At one point, it is even said, to extent, that the Earth had summoned them to exterminate the human race for causing so much environmental destruction.