The average life span of a rat is less than three years, but one pair can produce 2,000 offspring in a year. A group of rats is known as a "mischief." One pair of rats sheds more than a million body hairs each year. A single rat can produce 25,000 droppings in a year. Some rats can enter an opening as small as half an inch wide. Each year, rats cause more than $1 billion in damages in the United States alone. Some rats can swim up to a half mile in open water, dive through water plumbing traps, travel in sewer lines against the current, and stay underwater for as long as three minutes. Rats are known for gnawing anything softer than their teeth, including bricks, wood, and aluminum sheeting. Rats can jump 36 inches vertically and 48 inches horizontally. A rat can fall 50 feet without injury. Rats use their tails to regulate their body temperature, to communicate, and to maintain balance. Rats are color blind. Rats cannot vomit or burp. Carried largely by rats, the 14th-century Black Death killed about 25 million people - about one-third of Europe's population. 60% of the population of Venice died within 18 months.
My grandfather had a pet white rat, mama said he was jealous of the newspaper. he would jump out of grandaddy's pocket onto the newspaper and try to tear it up. I know we have some big woods rats here. My cat used to bring me live ones along with other varmints, mostly young. Rats can carry desease and so can their poop.
Rats are in the rodent family, which make up 40% of all classified mammal species. I had a heck of a time with them (Norwegian wood rats) at my last house, similar to @Von Jones' racoon problem. A developer bought a house on an adjacent lot to flip, and the thing sat in an unfinished state for over 10 years. Every time he disturbed the place, he chased his rats to my place. We had hamsters when I was a kid, but none of us had mice or rats. Regarding the poop that @Marie Mallery mentioned...I believe that the biggest health risk with rodent poop is after it dries and you disturb it. You don't want to breath that dust in.
The reason we’re feeding all the stray cats (7 now) is to keep the rats at bay. The whole neighborhood is mostly old houses with crawl spaces and to add to that there’s an open field behind our house so we’ve had a large problem with with the devil’s rodents. I’m tired of shelling out $35 a month just for poison which does kill them but leaves dead carcasses which in turn produces an odor that cannot be gotten rid of easily. Sometime this spring I am going under the house to rip out all the fiberglass A/C ducting, central chamber and the very expensive material that was laid to encapsulate the entirety of the crawl space which proved to be a wonderful homestead for breeding rats. I am then going to provide a small hole in the door to the crawl space for the cats to get in and out of so they can hunt.
This has actually turned out to work really well ! When we had the bad cold weather around Christmas, we put out food for the stray cats and made a bed on the porch for them to keep warm. They were coming up on the porch after we went to bed, and sleeping in Bobby’s chair out there, so the bed inside of a cardboard box gave them more shelter. After the freeze was over, we just kept putting food out, and word seemed to spread around the neighborhood cats that there was a Free Buffet at our house, and so more and more cats started dropping by. The large bag of cat food I am buying is a little cheaper than the rat poison, and we are feeding a creature and not poisoning one. The cats seem to be either catching the rats and eating them, or at least chasing them off, because we have not been hearing them under the house for the last month or so. And Bobby is making new friends, and giving me “cat reports” every day, and especially if a new one shows up. They now will stay on the porch and eat, even when he is outside; so they are getting used to a person being out there, and even trying to let him know when they need more food.
Rats are smart. There have been mice in my crawlspace since before I moved in. That's why there are so many snake sheds under there...the snakes are coming after the food. I was going to set up a bucket trap under there, and went on line to look at designs, when I stumbled upon some vids of this guy helping remediate a rat infestation. I couple of his vids made an impression. One of his night camera vids was of a series of regular snap traps has had screwed down to a board with dividers in between them (like public bathroom stalls.) He put seeds in the stalls without setting the traps several days in a row so the rats could get used to the free, safe buffet. He pointed out the smart rats that lingered back watching the dumb rats head right for the food. The smart rats waited to make sure it was safe. Then there's this guy:
As a kid I had mice. I bought one mouse. Suddenly there were more. And more. The cage didn't hold them, soon my dresser was all mouse nesting. I'd catch them and ditch them far from the house. A day or two later: more mice. It took a while to eradicate this nuisance.