Giant rat

Giant rats are simply an oversized version of these common rodents. They vary greatly in strength, from ones the size of a cat to ones bigger than humans, like their mole rat cousins. They can be annoying - the rats are hostile and will begin combat if you draw too near, severely delaying the player's passage through rat-infested areas. The species exists in the Mojave has acquired white hair, blue glowing eyes, are light brown color and is bigger than the normal species.

Small
The smaller rats are still big enough to rival a dog in size. They usually attack in large groups and could visually appear out of nowhere. They differentiate in color, being black, grey and even white. They appear in the Core Region, as well as in Texas.

Big
These rats are even bigger than the mole rats and humans. Their visible spine gives them a disturbing appereance, while their size and power could prove a challenge for an unexperienced wastelander. They can be found in the Midwest and Texas.

Fallout: New Vegas
A new species appears in Fallout: New Vegas, larger, are light brown color, blue glowing eyes and composed of white hair on his back. They usually don't attack but run away like bighorner.

Small
The smaller version is equal in size to a small dog, it's not very resistant and its damage is not dangerous.

Locations

 * One small giant rat can be found being chased by children in Freeside
 * Several can be found in Cerulean Robotics
 * Several can be found in Vault 11

Big
The bigger version is equal in size to a mole rat, cause of radiation excess, it became a little bigger and a little stronger than this smaller version.

It's not resistant but be warned, the bigger version is not a creature to be underestimated, it can kill a low wastelander within 3 hits and its attacks will go through armor. At low levels it's advised to avoid this creature, however it has a low DT and can be gunned down if the legs are crippled; this is advisable because they are normally quite fast and attack in groups.

Locations

 * Can be only found in the Broc Flower Cave