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Pest Library
Size: |
Roof rat (black rat, ship rat) adult head+body length
is 6-8 in (16-20 cm); tail length is 7-10 in (19-25 cm); weight is
about 5-9 ounces, up to 12 ounces. |
Characteristics: |
Soft, smooth fur; pointed muzzle; large eyes; large, almost naked
ears which can be pulled over the eyes. Scaly, dark tail is longer
than combined head+body length. |
Color: |
Brown with black mixed in, to gray, to black on top with white;
gray or black underside. |
Droppings: |
Adult droppings are up to 1/2 in (12.5 mm) long, and are spindle
shaped with pointed ends. |
Geographic Range: |
Probably from southeast Asia, but now found around the world. In
the U.S. Rattus rattus is most common in coastal and southern states,
especially near seaports. |
Comparison with other rodents: |
Norway rat (brown rat, house rat, wharf rat, sewer rat) is large,
has a blunt muzzle, small eyes, small ears that are hairy, a tail
that is shorter than head+body length, and is 2-colored; rod shaped
droppings with blunt ends. Hispid cotton rat has tail length about
half of head+body length, coarse fur that is grayish on top and mixed
buff, whitish and black on underside. House mouse is small, short,
with tail about same length as head+body; droppings 1/8-1/4 in (3-6
mm) long, rod shaped with pointed ends. Most native rats and mice
have hairy tails; or if tails are almost naked they appear to be ring-like
segments. |
Habitat: |
Outdoors: roof rats nest in high places such as trees, but sometimes
in burrows under plants. Indoors: they nest in high places in structures,
but sometimes in basements, sewers, or under buildings. |
Food: |
Roof rats eat almost anything, but they prefer fruit, vegetables,
and cereal products. They get their water often from their food. They
eat a lot at one time, and will return to that place time after time.
If they do not like a food or bait they quickly become shy of it. |
Biology: |
Roof rats mature in 2-5 months, and are adults for 9-12 months.
Pregnancy takes 3 weeks. Newborns get hair after 1 week, open eyes
after about 2 weeks, are weaned at 3-4 weeks. Female has 4-6 litters
per year, with 6-8 young per litter. They have keen hearing, smell,
taste and touch (long whiskers), but bad vision, and are color blind.
They are good at running, climbing, jumping, even swimming. They are
nocturnal and explore a lot, but are cautious and shy away from new
objects. |
Invasion: |
An opening larger than 1/2 in (12 mm) allows entry of roof rats
into buildings. |
Damage: |
Roof rats gnaw, 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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