Porges, Arthur – “The Rats” (1951)
Jeffrey Clark, physicist-turned-kook, has set up shop in a fake village built by an atomic testing ground to await real atomic war. He enters into a slow-burning showdown with a colony of rats also in residence, who seem to be directed by one over-sized albino rat. He very, very, very, very slowly realizes that they are mutants and he is being outwitted, and this is supposed to be horrific, but it’s totally lacking in tension. Oddly, mutant telepathic rat-kings are also a feature of Deus Irae.
The climax comes when one of Clark’s traps backfires and he is stuck in a shed that’s been set on fire – when he hears a series of booms outside and understands that the end has arrived.
Putting his gun to his head, he roars:
“You out there! You win, damn you! You may be the only ones left this time next month! It’s all yours now. And what the hell will you do with it?” Then he squeezed the trigger.
Compare with Asimov’s “No Connection” (1949), another story about post-human-extinction animal takeovers, although in a vastly different time frame.