Also
known as the house rat, brown rat, wharf
rat, gray rat, sewer rat, and water rat,
the Norway rat was first introduced to
the U.S. by European settlers and
trading ships around the year 1775.
Since then, the Norway rat has
become the most prevalent rat in the
United States. This rat is better
adapted than other species to survive
and produce young in cold climates.
Norway rats are large and robust,
weighing between 12 and 16 ounces.
Although reports of larger rats have
been documented, these instances are
rare. Length of the head and body
combined average 7 to 9.5 inches and the
tail measures 6 to 8 inches. Their fur
is coarse and ranges from reddish to
grayish brown; many variations and color
combinations are possible. The tails of
Norway rats are mostly devoid of fur and
scaly. Their eyes are small, they have
blunt noses, and their ears are small
and covered with short hairs. To
identify a Norway rat by its droppings,
look for capsule-shaped excrement
measuring ¾” to 1” in length.
Some interesting characteristics of
Norway rats include amazing physical
abilities. They are excellent swimmers
and can stay submerged in water for up
to three minutes. They can swim a ½ mile
in open water, tread water for three
days, and travel through sewer lines
against substantial currents. Also, they
can jump from a standing position 3 feet
vertically and can drop down 50 feet
without any threat of injury.
The Norway rat is generally a ground
dwelling animal. It frequently nests
outdoors in underground burrows. On
farms, they may live in barns, livestock
buildings, granaries, and silos. In
cities, rats may spend their entire
lives in buildings or outside in the
ground where space is available. They
inhabit all types of building structures
including warehouses, hotels, food
facilities, residences, and stores. They
are also commonly found in dumps and
sewers and can be found living near
ponds, lakes, or in parks.
Rat nests found in buildings are
typically on lower floors. However, if
an infestation is large, they may move
up to attic areas, upper floors, or into
suspended ceilings. They can also be
found in wall voids, underneath floors,
and in crawl spaces. In some city
dwellings, rats have been bold enough to
live in furniture in occupied homes.
When building their nests, almost any
soft material is sufficient for their
bedding.
When rats burrow outside, they usually
nest near the side of foundation walls.
The underground burrows start out
measuring 12 to 20 inches in length, but
grow as the number of rats populating
the burrow grows. After time,
underground tunnels may connect several
burrows. When this happens, there is
always one main entrance and two
additional openings called bolt holes,
which are used for sudden escapes.
Rats require 1 ounce of food daily,
which is 10 times the amount needed by
mice. They eat all kinds of food,
although they generally prefer nutrition
with high amounts of carbohydrates and
protein. Household trash is an excellent
source for achieving a balanced diet.
Cereal grains, meats, fish, livestock
feed, and fresh fruits and vegetables
are ideal nutritional sources.
If rats are living outside, they will
search for food outside. However, if
there is no food available outside, they
will enter indoor locations at night and
then reenter their outdoor burrows once
their food search is complete. If a rat
has taken up residence in a field or
wooded area, he or she may kill and eat
small animals, birds, and insects. In
sewers, rats are fond of American
cockroaches.
Rats need ½ to 1 ounce of water daily if
feeding on dry food and less if feeding
on moisture-rich food. Unlike mice, rats
cannot survive very long without water.
To ensure the necessary amount of
hydration, rats will obtain water from
sinks and toilets, puddles, condensation
on pipes, and early morning dew. Rats
will resort to extreme lengths to obtain
their food and water. They have
excellent climbing abilities and will
climb up stairs, pipes, wires, and walls
to get into buildings.
Rats are nocturnal, and generally feed
at dusk and just before dawn. If you see
rats during the day, this is a sign of a
heavy infestation. It can also mean that
the rats are really, really hungry or
that they were disturbed.
Like mice, rats have territories. The
radii of these territories usually range
from 50 to 150 feet from the nests. When
there is abundant food available and the
rat population is high, territories will
be lower in area. If the opposite is
true, rats can travel up to 300 feet in
search of food and water. Rats in urban
areas tend stay in the yards in which
they find food and water.
Although rat families may share food and
water sources, this atmosphere of
sharing will disintegrate once the
population rises. Competition and
fighting increase along with the
population, and this results in a
population divided into “social orders.”
These orders are comprised of
dominant rats and weaker rats. Dominant
rats get first selection of lodging and
food. The weaker rats are forced to live
the farthest away from food sources. As
a result, the weaker rats have to feed
when the dominant rats are inactive,
during the day. For this reason, daytime
rat spottings are a sign of heavy
infestation.
Rats often have a condition called “neophobia,”
which means “fear of the new.” After
exploring and becoming acquainted with
their surroundings, rats are acutely
aware if anything is out of place or
newly introduced, such as traps and
baits. Neophobia can last anywhere from
several hours to several days-- this is
why traps and baits may take several
days to become effective.
Breeding peaks in the spring and fall of
every year and tapers off in the summer
and winter.
After mating and a gestation period of
about 22 days, the mother rat gives
birth to a litter of 8-12 pups. The
young are naked and blind at birth.
Their eyes open in about 9-14 days, and
they are weaned 10 to 15 days later.
Rats reach sexual maturity at an average
age of 3 months. Under ideal conditions,
maturation can happen at 8 weeks.
Females can go into heat every 4 or 5
days, and have the ability to mate
within a day or two after a litter is
born. The average female rat has 4 to 7
litters per year, and may successfully
wean 20 or more pups annually.
Captive rats may live up to 3 years. In
the wild however, they usually live only
5-12 months. Rats face destruction by
predators, other rats, people, disease,
and stress.
back to top
