So, if zombie inducing flies switch from ants to Texans, how long before anyone notices?
When their heads start falling off.
Texans without ten-gallon hats will be conspicuous.
One of the major, major problems with fire ants is that they will nest inside telephone junction boxes, and they think the insulation on the wires is yummy beyond belief. They will also eat the insulation off of incoming power wires to houses, and that can start fires.
Let’s see.
The flies eat the ants’ brains. Then they start eating Texan’s brains, which is noticed when Texans start forgetting to impose the death penalty in criminal trials.
Then they bring in cane toads to kill the flies, which ends up killing all the hound dogs who lick the toads.
Then they nuke it from orbit, because what good is Texas without hound dogs?
I hate to be the one to rain on your parade, but “silver bullet” is a stock idiomatic expression for "something that acts as a magical weapon ; especially : one that instantly solves a long-standing problem." No monster-movie reference intended.
The case is known as Australia 
Somehow, it doesn’t surprise me that Anne Neville sides with the zombies.