I live in southern FL, and just bought a house with a flat roof. One of the first things I did was cover all the plumbing vents with nylon screening to keep cuban tree frogs out of them (they love pipes, and can clog up your plumbing. I found one in my toilet once). A week later, I noticed the screen was off the large 4" vent, I thought it odd that it would blow off, but replaced it. I was just on the roof, and noticed the screen was still over it, but a good size hole had been chewed through it (I don't know if something wanted to get in or out). Frogs don't have teeth, so I don't think that's the culprit. What could it be? Would a squirrel live in a vent?