I don't believe they are eating pets and animals "yet" And it's probably a red herring, untill that lady who made a post claiming to see her cat swinging from a tree being butchered somehow forgot to take her phone with her at that time, or report it to the police shows some evidence of it.

But "Springfield" is a perfect place for "something" to happen because Springfield perfectly ties to the Simpsons. A cultural touchstone of an America that no longer exists. A small enough town is a great place for things to happen. Hopefully it's small enough that there's enough community to cover for each other, but given the urban dude who was at the city council meeting, I suspect the town has already been colonised.

Sad.