Norway (Dumbo) rats rarely bite, and our Roof Rats never bite (even nursing females.) If biting is a concern for you, we recommend Roof rats over Norway rats. The differences between Norway rats (rattus norvegicus) and Roof rats (Rattus rattus.)
If a female rat is nursing young, and you try to disturb them, even the tamest new mommy might become aggressive and snap at you. I breed rats, so I certainly have been bitten by some moms with babies. Sometimes it took some gentle prying to get the rat to release it’s grip.
But you cannot fault them for just trying their best to be good momies. It’s touching, really. to see how hard rat moms work to feed and care for their young, bless their little hearts!
Aside from that, I’ve never been intentionally bitten by one of my rats. I’ve met some rats owned by others that I wouldn’t trust with my fingertips, but they were abused and neglected. And even abused and neglected rats can be surprisingly friendly, because most rats crave friendship and companionship.
Rats have teeth, and any animal with teeth is capable of biting. But most rats would prefer to make friends than enemies. So, unless you go out of your way to torment and abuse your pet, and corner them so they cannot escape or avoid you, you will most likely not be intentionally bitten.