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Pest Library
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. |
Color: |
Norway rats are brown with scattered black hairs, gray to yellow-white
on underside. |
Droppings: |
Adult droppings are up to 3/4 in (20mm) long, capsule shaped with
blunt ends. |
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. |
Comparison with other rodents: |
Roof rat is lighter in color than the Norway rat, and has a pointed
muzzle, larger eyes, larger ears; is uniformly colored, almost naked,
and has a tail that is longer than the combined head+body length;
droppings are spindle shaped and pointed at ends. Hispid cotton rat
has a tail length of about half of its head+body length, coarse fur
that is grayish on top and mixed buff, whitish and black on underside.
House mouse is small, short, with a tail about the same length as
head+ body; small droppings that are 1/8-1/4 in (3-6 mm) long, and
rod shaped with pointed ends. Most native rats and mice have hairy
tails; if not hairy, they look like they are made of ring-like segments. |
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. |
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. |
Invasion: |
An opening larger than 1/2 in (12mm) permits entry of Norway rats
into structures. |
Damage: |
Norway rats gnaw objects, eat stored food, and transmit disease
by droppings and urine, bites, and the fleas and mites in their fur. |
Detection: |
- Gnaw marks.
- Droppings.
- 4-toed front footprint in front of longer 5-toed hindprint.
- Dark greasy markings from fur rubbing against surfaces.
- Shallow burrows under plants.
- Greasy runways along walls and bare soil runways outdoors.
- Nibbled food.
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