Leinster, Murray [as by Will F. Jenkins] – “Doomsday Deferred” (1949)
An American goes to Brazil hunting butterflies, but finds instead a colony of army ants that has evolved a kind of telepathic hive mind. As is the case with so many of the protagonists of this era, he immediately grasps the situation and makes a number of leaps of logic that we are presumably supposed to also understand as being correct – if the ants can communicate with one another, surely they will soon be able to control the minds of other animals and then humankind, and will take over the world. He tricks “the Something” into eating poisoned cattle and saves the day.
The Brazilians are “unwashed,” gullible, and superstitious, and are unfamiliar with the concept of cocoons, which they call “the small nuts with worms in them.” The American, meanwhile, is a man of science – approaching hysteria at one point, reminds himself that “my actions were not those of a reasoning human being. I did not think with proper scientific skepticism” (while the creature, notably, is described as being naïve for not understanding the power of its ESP).