Pest Library
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Norway Rat (Brown Rat, House Rat, Wharf Rat, Sewer Rat)
Rattus norvegicus (Berkenhout)
These 9-inch rats usually live in groups, which means where there is one, there are likely others. Norway rats produce an average of 20 young per year and will fight for food, even if it means chewing through plastic. They pose a number of threats to public health, including disease and bites to humans and animals.
RISK LEVEL:
LOW
MEDIUM
HIGH
Risk is defined as how much damage each pest can be to you, your family, or your home
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| Class: | Order: | Family: | |
| Mammalia | Rodentia | Muridae | |
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| Size: | Norway rat adult's head+body length is about 7-9 in (18-25 cm ); tail length is 6-8 in (15-21 cm ); weight is 7-18 ounces, up to 20.5 ounces. |
| Color: | Norway rats are brown with scattered black hairs, gray to yellow-white on underside. |
| Characteristics: | Heavy body; coarse, shaggy fur; blunt muzzle, small eyes, small ears with dense short hairs; scaly, 2-colored tail, which is darker on top, and is shorter than the length of its head+body. |
| Geographic Range: | The Norway rat, which is also known as the brown rat, house rat, wharf rat, or sewer rat, is probably from central Asia, but now found around the world, and throughout the U.S. |
| Food: | Norway rats eat anything, but they prefer meat, fish, cereal, and dry dog food. They require a water source other than their food. They eat a lot at one time, returning to the same place, but quickly become shy of undesirable food or bait. They will travel to find food or water, gnawing through almost anything, even plastic or lead pipes. |
| Biology: | Norway rats are social. Many burrows may be in the same area. These rats mature in 2-5 months, and live as an adult for 6-12 months, longer in captivity. Pregnancy lasts 3 weeks. Newborns get hair after 1 week, open their eyes in 2 weeks, and are weaned at 3-4 weeks. A female has 3-6 litters per year, 7-8 young per litter, with an average of 20 young weaned per year. They have keen hearing, smell, taste, and touch, with their long whiskers, but poor vision, and are also color blind. They can run, climb, jump, and swim. They are nocturnal, and explore a lot, but they are cautious and shy away from newly introduced objects. |
- Check for gnaw marks.
- Watch out for droppings.
- Look out for four-toed front footprints and longer 5-toed hindprints.
- Be aware of dark, greasy markings that are the result of fur rubbing against surfaces.
- Check under plants for shallow burrows.
- Look outdoors for greasy runways along walls and bare soil runways.
- Check for tiny nibbles in food.