Winner of the Nebula Award 1979.
I read this in a collection of Nebula winning stories edited by Frank Herbert. I see why it won the award, though this probably seems tropish in the modern era. The 1970s were full of giant monster movies. Various explanations were made for the giant monsters; nuclear fallout, toxic waste, alien invasion.
This story uses an entirely different approach, but it leads you to assume giant monsters. And it keeps you reading until the very end, just to get to the bottom of the mystery.
I don’t think I’m going to give you any more than that, because it will create spoilers, but it’s certainly worth a read while you’re waiting in the doctor’s office! An entertaining tale!