Palo Alto is infested rats, I suspect the many lush overgrown gardens don't help. I've even seen them running down the power lines. A good pellet gun and a case of Beer make quick fun on my back porch.

Santa Clara County has a rat problem AND a termite problem. Termites are a favorite snack of rats, so if you have a rat problem in your home, you may have a termite infestation!

One of the reasons for year-round termites, and thus, a rat problem, is that the SF Bay Area never has snow, nor a long, hard, killing frost.

Most of the northern hemisphere has cold enough winters to severely reduce the termite population-- except the Mediterranan area and the Bay Area.

It comes in waves depending on the area. In MV we lost entire summer harvests until we started putting up bird netting (best barrier I have found) Back then electric traps were new and ruthlessly efficient. I caught 3 withing a 2 hour span one evening using the same trap. Now they seem to know to avoid it, and though the numbers have diminished over the years, we still need to watch. Once they find the food, they'll keep coming back, but now that the population has decreased some, it's not as bad. That nsaid, you can watch them run the wires each and every night. They're not going away; think of them as night squirrels

We're overrun with squirrels and occasionally have seen rats. Ick. I suggest this as a topic for neighbor discussion - because with most homes and yards so close together, it takes a neighborhood to make a difference. Discuss how everything like pet food must be covered up outside, garbage lids solidly on, excessive foliage trimmed back, dropped fruit picked up in the yard, etc. This will help to reduce the rodent and vermin populations...I hope.