Whilst the correct common name is the Norway rat, it is more commonly called the brown rat, sewer rat, common rat or wharf rat.
The brown rat (sewer rat) is an invasive rodent.
Found worldwide, adapts well to most climatic conditions. In Australia, in contrast to most of the rest of the world, the brown rat is less common than Rattus rattus (the roof rat).
The brown rat (Norway rat) is mainly a ground dweller, so will commonly be found nesting in burrows, often located under tree roots, ground cover plantings, slab edges and flooring.
In cities they will often live and nest in the sewers, which gave rise to their name, the sewer rat.
The Norway rat is a prolific breeder and a female can have 6-10 young in a litter and 3-6 litters per year depending on availability of food. They are happy to intra-breed within families. Social groups are often formed of multiple males and multiple females. One male is dominant. Two to three females are often dominant to all other group members except the dominant male. Lifespan in the wild is 12-18 months.
Colour: Variable – Dark grey or brown to black with a lighter underside
Size range (adult): Body 15-25 cm, Tail 10-20 cm, Weight: up to 500 g
The Norway rat is stocky with a blunt nose, small close-set ears and a long naked tail. It is a significantly bigger animal than the roof rat, but despite this, it is less common in Australia.
Brown rats (Norway rats) are omnivorous and will eat a wide range of foods, including seeds, fruit, stems, leaves, fungi, and a variety of invertebrates and vertebrates. Their diet will vary depending on what is readily available. They will eat just about anything that a human might consume. An adult will eat 15-30 g of food in a day.
Brown rats (Norway rats) will spread disease in various ways. Their urine and faeces will transport infections and their fur is recognised as being a carrier of several bacteria. Diseases of note include Leptospirosis, Salmonella, Hantavirus and others.
With their liking to forage in garbage and in the sewers, gave rise to their name the sewer rat.
Good housekeeping is primary in reducing the likelihood of a Norway Rat infestation.