This is a vent on the side of our house (it's not exactly an attractive part of our house, but bear with me):
About thirty years ago, our roofer Carl was an exterminator who dealt with rats and termites. When Carl was at our house on Tuesday, he noticed this vent and told me that rats could get into our house through the hole in the wire mesh.
Rats? RATS?! OH MY GOD I HATE RATS THEY ARE SO CREEPY ESPECIALLY SUBWAY RATS OH I HATE THOSE BUBONIC PLAGUE INFESTED RODENTS!!!!
Fortunately, Carl told me an old exterminator's trick: rat's hate steel wool. If you stuff any holes in your house's vents with steel wool, that will keep the little bastards away.
I already had plans to go to Target, so I picked up some steel wool pads and viola:
The holes in our side vents are plugged with steel wool and any neighborhood rats will just have to seek shelter elsewhere. DIE RATS DIE.