Somehow I just had another false memory moment related to an early-2000s Disney IP - I was convinced that The Buzz on Maggie's backstory is that the flies became anthropomorphic from nuclear pollution but the show didn't ever use it for either conflict or jokes, but a few fandom Wiki visits later and nope. I made it all up. I have no clue where I got that fake piece of trivia from either, I haven't watched or read any Buzz on Maggie content lately so I don't know how this came to mind.