Ralph Williams' "Cat and Mouse" (novelette, science fiction, free): A colorful pest control problem!
Story summary.God-like aliens maintain cosmic scale game parks. One such park is "World 7" where a "natural ecology was being maintained ... as a control for experimental seedings of intelligent life-forms in other similar worlds."
But the park Warden has got a problem at hand - in some unexplained way, a pest called the Harn has reached here, & is threatening to overrun the game!
Harn is a carnivore, & a rather efficient hunter. And it's not a single animal, but a colony of animals specialized for various tasks. "The Harn" is the nerve center of this complex organism - itself an animal that does most thinking but is not very mobile, & can (apparently telepathically) communicate with mobile units. And in the manner of the parrot containing the soul of evil magician kids' tale (was it from Arabian Nights?), killing Harn will kill off the entire hive - even animals currently physically far off.
Warden doesn't like killing animals in the park, not even pests. And he doesn't fancy the idea of introducing natural enemies of Harn in the park. But he has an idea - involving a somewhat intelligent animal from a nearby world. Not difficult to guess his chosen pest killer - humans.
So a transfer gate magically appears "not fifty feet" from the cabin of Ed Brown, living only with his dog somewhere in interior Alaska. Ed is in his sixties, is well versed in living off nature, is well stocked with guns, & is technically competent in rigging up gadgets from available material.
The gate is in the form of vertical "six by three" opening, as a door, just standing in the wilderness. From one side of it, you can see the other world & even move into it just by walking across (& similarly return). It doesn't exist if you trying seeing if from what would normally be its "back" side. Gate opens in the area of World 7 inhabited by Harn.
Story is mostly of Ed's cautious adventures across worlds. Attack on him by a mobile unit of Harn, his retaliation that bothers Harn, his attack on Harn's nest, Harn's very determined counter attack, & ultimately killing of Harn at the hands of Ed. Ed doesn't escape unhurt, but Warden's god-like powers will save him.
- Clifford D Simak's "The Big Front Yard": Another story where you just walk across a door to reach another world!
Fact sheet.First published: Astounding Science Fiction, June 1959.
Nominated for Hugo Award 1960.
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Credits: I found this story via QuasarDragon.