The Norway rat (Rattus norvegicus) is one of the most widespread commensal rodents globally, thriving in close association with human populations in urban and suburban environments. Often called brown rats or sewer rats, these robust, burrowing creatures are common across continents due to their adaptability. Concern about their temperament is understandable, but their behavior is primarily motivated by survival and avoidance. Understanding their natural disposition helps comprehend the rare instances when aggression is displayed.
The Standard Behavior of Norway Rats
Norway rats are naturally cautious and rely heavily on their senses of hearing and smell to navigate an environment where they are often prey. The baseline behavior of a wild rat is characterized by neophobia, a reluctance to engage with anything new or unfamiliar in their territory, including traps or sudden changes. They are primarily nocturnal, active just after sunset and before dawn, specifically to avoid encountering humans and other predators.
Their movements are typically limited to established runways as they forage for food, water, and shelter, which are the main drivers of their activity. A rat’s immediate instinct when confronted by a larger animal or a human is to flee and seek the nearest cover, a strategy known as “flight over fight.” This avoidance mechanism means most encounters are fleeting glimpses of a retreating animal. They prefer to live in colonies, often establishing a complex network of burrows up to six and a half feet long near foundations or under debris.
Situations That Cause Defensive Attacks
Aggression in Norway rats is almost exclusively defensive, occurring only when a rat feels its life or resources are directly threatened and escape is impossible. The most common trigger for a defensive strike is being cornered, such as when a rat is trapped inside a structure or physically blocked by a person or pet. When retreat is impossible, the rat shifts from avoidance to self-defense as a last resort.
Specific defensive behaviors serve as clear warnings before a physical attack. These include standing on the hind legs in a boxing posture, chattering the teeth, and emitting long squeaks or hisses. Their fur may also become piloerect, standing on end to make the animal appear larger and more intimidating to the perceived threat. If the threat persists, a defensive attack is typically aimed at the face of a smaller animal, as the rat attempts to protect its vulnerable rump and flank from injury.
Maternal aggression is a highly specific trigger, where a lactating female vigorously defends her nest and young against any perceived intruder. This protective instinct can lead the mother to lunge at or bite an animal or person who gets too close to her litter. Aggression also occurs in the context of territorial defense, particularly among dominant males who attack unfamiliar rats that intrude on their established colony area. Unusually bold or erratic daytime behavior, though statistically rare, can sometimes indicate a rat is ill, causing it to act outside of its normal cautious temperament.
Preventing Unwanted Encounters
Minimizing the chance of a defensive encounter involves proactive habitat modification and exclusion techniques that remove the rats’ motivation to remain nearby. Exclusion focuses on sealing potential entry points into structures, which is a relatively permanent method of control. Norway rats can squeeze through openings larger than half an inch. Therefore, all gaps around utility lines, foundations, and vents must be sealed with heavy materials like concrete mortar, galvanized sheet metal, or heavy-gauge hardware cloth to resist gnawing.
Sanitation practices are equally important, as they directly reduce the rats’ primary resource: food. All outdoor garbage containers must have tightly sealed lids, and pet food should never be left outside overnight. Any bulk food, including bird seed or livestock feed, should be stored in metal or other rodent-proof containers with secure seals.
Reducing available harborage eliminates the shelter rats require to nest and hide, further discouraging their presence. This involves removing debris, stacked lumber, and woodpiles from around the perimeter of structures. Controlling weeds and keeping grass mowed short limits the dense vegetation that provides cover for their travel and burrowing activities.