Here's a few bits from Robert Sullivan's Rats: Observations on the History and Habitat of the City's Most Unwanted Inhabitants.
Jack Black isn't just an actor. He was Queen Victoria's rat catcher and started a fad among Victorians of keeping pet rats as pets. Beatrice Potter is said to have bought a rat directly from Jack. Sullivan theorizes that the strand of laboratory rats are descended from Black's rats.
26% of electric cable breaks and 18% of phone cable breaks are said to be caused by rats. It's estimated that 25% of fires of unknown causes are actually started by rats. One estimate is that one third of food production is destroyed by rats.
Rats have sex up to 20 times a day. If no females are available, male rats have sex with each other.
Rats are thigmophilic - they love to touch things
By 1926, Norway rats (not really from Norway) were living in every U.S. state. The last holdout was Montana which had difficult terrain and few people to feed off of. Alberta calls itself a rat-free province but this is probably not entirely true (a mayor of an Albertan city said that he would eat any rat found in town. He recanted when presented with a basketful).
The one rat per person myth debunked
"A woman said to me, 'Oh, we're goin to get a cat!' he [an exterminator] recalled. 'I said, "Miss, please don't put that cat in the cellar,' Then I came back two weeks later and I'm picking up the hair and the bones of the cat."
Cockroaches don't fly because they don't have to. One exterminator compared it to people rolling around in wheel chairs and not using their legs, getting enough to eat without walking.
The Bubonic Plague came to San Francisco near the turn of the 20th century but was covered up by politicians and business leaders (a la Jaws). Health officials reporting the plague were fired or threatened with arrest. Eventually it was contained but the plague spread throughout the American southwest. Today there are more rodents infested with bubonic plague in America than were infected during the height of the plague years in Europe.
Chickens are not susceptible to the plague. Scientists at the Pasteur Institute injected live plague bacteria into a chicken to study the reaction. Naturally, the chicken escaped and was found by a local. He cooked and ate it with his family. They suffered no ill effects but the consequences of eating plague-infected poultry is probably not conclusive until further studies.