Norway Rat
Rodent—Norway Rat
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.
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. Adult droppings are up to 3/4 in (20mm) long, capsule shaped with blunt ends.
Color
Norway rats are brown with scattered black hairs, gray to yellow-white on underside.
Where
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.
Habitat
Outdoors, burrows of Norway rats are in the soil along railroad embankments, river banks, rubbish piles, and under concrete. Burrows have hidden emergency exits.
Diet
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.
Damage
Norway rats gnaw objects, eat stored food, and transmit disease by droppings and urine, bites, and the fleas and mites in their fur.
Invasion
An opening larger than 1/2 in (12mm) permits entry of Norway rats into structures.
Detection
1. Gnaw marks.
2. Droppings.
3. 4-toed front footprint in front of longer 5-toed hindprint.
4. Dark greasy markings from fur rubbing against surfaces.
5. Shallow burrows under plants.
6. Greasy runways along walls and bare soil runways outdoors.
7. Nibbled food.
Control
1. Concentrate control where most droppings are found. Use traps or bait stations along runways and against vertical surfaces. Wire glue boards to rafters and pipes.
2. Norway rats are cautious: pre-baiting with nontoxic bait may be needed.
3. They're gluttonous: use sufficient bait for at least 1, 2 or more meals with appropriately labeled baits.
4. Norway rats like meat: use high-protein baits, or liquid baits if water source can be reduced or eliminated. Burrows may be gassed.
5. Read entire label of pesticide registered for these species, strictly follow label directions, restrictions and precautions.