On the "Pentagon Library terminal" in the Citadel, it can be discovered that the mole rats in the Capital Wasteland (and possibly the other mutated rats in the west coast and the Core Region) are the result of an American government program (codenamed 'CLOACINA') to develop an invasive lifeform that could be planted in China, where its aggression and fast breeding would help undermine the Chinese war effort. It is noted that a genetic 'kill switch' was included to help the US Army clean up the rats after the theoretical fall of China. Additionally, it is revealed that the researchers attempted to use the Forced Evolutionary Virus to further augment their creations, but dismissed this course of action as FEV had a tendency to render subjects sterile (defeating the whole purpose of the rats' being invasive).
Mole rats are relatively caring parents, willing to sacrifice their own life for the well-being of the pups. Mole rat families travel in groups of usually three to seven, consisting of two to three adults and one to four pups. These families are moderately docile, keeping to themselves unless approached by an enemy. Even though they are almost blind, they can smell and hear quite well.
Mole rats are usually found in small packs, usually away from the main populated areas. Although relatively weak, they can be a threat for lower level players when encountered in large packs. Mole rats will attack if approached, and usually charge at the player.
Mole rat pups are mole rats that have yet to mature. Being younger, pups are smaller as well as weaker than adult mole rats. They are usually found around other mole rats, presumably their parents, wandering around the Wasteland.
There is a unique tame mole rat found at Sloan named Snuffles, whom the Courier can talk to and, with Medicine skill of 30, can mend Snuffles' wounded leg. Chomps Lewis will give the player NCR money as a reward upon accomplishing this task, and they will also gain Fame with the NCR.
Four friendly mole rats spawn at the mole rat ranch, but are usually killed by a hostile brahmin.
All mole rats are friendly if the Courier has the Animal Friend perk.