A widely travelled and adept swimmer, the Norway rat is a challenging pest to control. Understanding its biology is key for success.  

When professional pest managers delve deeply into rodent biology and behaviour, it becomes easier to accurately identify pest species and use best practice management strategies, which serve to enhance rodent control outcomes. Here we take a closer look at one particular pest rodent species: the Norway rat (Rattus norvegicus), also known as the brown rat, sewer rat, wharf rat, water rat, street rat, and Norwegian rat.


Pest status

The Norway rat (Rattus norvegicus) is among the most ubiquitous of rodents. It lives in close proximity to humans, seemingly having an unrestricted capacity to reproduce. It is the cause of extensive economic damage to ecosystems, farms, industrial properties and households by contaminating food supplies and spreading disease.


Key behaviour

Norway rats are generally nocturnal, often active around dusk and pre-dawn, when they tend to their nests, dig burrows, and hunt for food. The Norway rat, commonly known as a ‘water rat’, may be seen in locations near water and is a proficient swimmer. Norway rats typically have a complex network of underground tunnels with multiple entry and exit holes for escape, often hidden under grass, rubbish, and other debris. Being extremely sociable animals, they create groups that are maintained according to a dominance hierarchy. Members of the group are frequently quite hostile towards strangers. Each group is led by a dominant male who may mate with numerous females and occupies the best parts of the group’s territory. These societies frequently engage in collective nursing, when females assist in caring for the young of another female. Some females, meanwhile, have exclusive nesting burrows of their own.


Quick facts

Identification: Large size rodent with a blunt nose, small eyes, and close set small ears

Weight: 250-400 g

Body length (head and body): 19-26 cm

Total length, including tail: 45 cm

Sexual maturity: Reached in 2-3 months

Gestation period: 23 days

Number per litter: 6-12

Number of litters: 4-7 per year

Daily food intake: 30 g

Life span: 18 months

Droppings: Around 15 mm, with blunt edges


Inspection tips

When conducting a site inspection, it’s important to look for the signs of their presence. Look for burrow entrances and traffic routes in the landscape, such as along pipes, ledges, and inside roof voids. The areas they frequent can be identified by rub marks (caused by grease and dirt from their bodies), footprints (running tracks), damage (gnaw marks), droppings or nests.


Did you know?

The tail of the Norway rat is shorter than its head and body combined.


Gaining control

It’s crucial to identify the signs of the rodents’ presence and place bait stations or traps in these traffic routes and locations. For areas of high infestation, bait stations must be inspected frequently to ensure bait supply is maintained in all stations until the rodent population is under control.


Preferred food

Norway rats prefer fish, meat, grains and high protein foods.


Recommended baits

Norway rats are creatures of habit and display neophobic behaviour towards new objects. If they eat something they dislike, Norway rats will quickly develop an aversion to that food and search for an alternative option. Once they find a favourable food source, Norway rats will return time and again.


This is one of the reasons why Liphatech developed and drove the innovation into soft bait formulations. Difethialone, discovered by Liphatech, has superior efficacy on both rats and mice and is available in First Strike Soft Bait, which is a mixture of milled grain and vegetable oil which has no wax and is highly palatable. It is also easy to use, making it a good choice for challenging Norway rat jobs. Those who prefer a more traditional bait can opt for Generation Block, which also contains difethialone, in a 15 g punchy extruded block bait form. Liphatech recommends rotating rodent baits for best practice. Liphatech also offers a range of bromadiolone baits in both soft and block form and hardware products suitable for use on Norway rats.