Aliens (The Screwfly Solution)

This is an unnamed species of beings which look vaguely like angels, spirits or fairies. They have engaged in a successful or nearly successful attempt to exterminate the Human species on Earth, doing so by creating an airborne agent that stimulated the minds of male Humans and caused them to become homicidally aggressive towards the females. Whether they ultimately succeeded in conquering Earth is never revealed, but it is presumed that they did.

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 Alstein tries to save her daughter during the onslaught but loses her to her affected husband Alan. During the onslaught, a new religious movement composed entirely of male Christians called the Sons of Adam is spreading along with the murders, and they believe that women are evil, that the Garden of Eden was a paradise with the first man Adam living alone in a state of innocence and bliss before the birth of the first woman Eve, and that God is telling them to get rid of all of the women. When the cult's warped religion initially arises, prior to the organized murders, little is done to stop the spread of their ideology, nor are their actions of evicting women from the areas the men control prevented. Alan realizes that the disease causes male sexual impulses to instead become violent impulses. Alan, a sensitive, kindly man, realizes that he himself is succumbing and tries to resist the impulses, as well as isolate himself from women. 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. Like the story, among the men in the world infected by the screwflies is a fanatical misogynistic cult known as the Sons of Adam who were mentioned by the scientist Dr. Alan Alstein who also said that they are not behind the epidemic, merely the victims of it. Following the death of her daughter, Anne Alstein 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, a typical conquering alien race that met this goal by corrupting the sexual drive of the Earth's human males 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.