Solitary or Social? People commonly believe that if there's one rat in a house, more will so on follow. However, determining the exact number of Norway rats living in a space is difficult, especially indoors. For outdoor burrows, the rule of thumb is one to five rodents per burrow, so Norway rats do live alone sometimes. Females are more likely to live on their own when raising their young. Norway Rat Colonies Norway rats are adaptable and able to live together in low densities as well as high densities if needed. Frighteningly, some colonies can number in the hundreds. The larger the population, the more aggressively males will act toward one another. Removing Infestations Residents of infested homes should assume they are dealing with more than one Norway rat. Eliminating one rat and thinking the problem is solved can be dangerous and hazardous to health. The professionals at Critter Control can stop an infestation before it gets out of hand.