The Norway rat (Rattus norvegicus) is a stocky burrowing rodent, unintentionally
introduced to North America by settlers who arrived on ships from Europe.
into the United States about 1775, this rat has now spread throughout the contiguous 48
states. The Norway rat is found generally at lower elevations but may be found wherever
Norway rats live in close association with people. They burrow to make nests under buildings and other structures, beneath concrete slabs, along stream banks, around ponds, in garbage dumps, and at other locations where suitable food, water and shelter are present. On farms they may inhabit barns, granaries, livestock buildings, silos, and kennels. In urban or suburban areas they live in and around residences, in cellars, warehouses, stores, slaughterhouses, docks, and in sewers. Although they can climb, Norway rats tend to inhabit the lower floors of multi-story buildings.
Norway rats will eat nearly
any type of food. When given a choice, they select a nutritionally balanced diet, choosing
fresh, wholesome items over stale or contaminated foods. They prefer cereal grains, meats
and fish, nut, and some types of fruit.
General Biology, Reproduction and Behavior
Norway rats are
primarily nocturnal. They usually become active about dusk, when they begin to seek food
and water. Some individuals may be active during daylight hours when the rat population is
high, when disturbed (weather change, construction, etc.) or when their food source is
Rats have poor eyesight beyond three or four feet, relying more on their hearing and their excellent senses of smell, taste and touch. Norway rats are very sensitive to motion up to 30-50 feet away. They are considered essentially colorblind.
Rats use their keen sense of smell to locate food items and apparently to recognize other rats. Norway rats rely on their sense of smell to recognize the odors of pathways, members of the opposite sex who are ready to mate, differentiate between members of their own colonies and strangers, and to tell if a stranger is a strong or weak individual.
Norway rats use hearing to locate objects to within a few inches. This highly developed sense (combined with their touch sensitivity) can pinpoint someone rolling over in bed to a six inch area. The frequency range of their hearing (50 kilohertz or more) is much higher than that of humans (about 20 kilohertz.)
Norway rats have a highly developed sense of touch due to very sensitive
body hairs and whiskers which they use to explore their environment. Much of a
rodents movement in a familiar area relies heavily on the senses of touch and smell
to direct it through time-tested movements learned by exploration and knowledge of its
Their sense of taste is excellent, and they can detect some contaminants in their food at levels as low as 0.5 parts per million. This highly developed taste sensitivity may lead to bait rejection if the rodent baits are contaminated with insecticide odors or other chemicals.
Norway rats usually construct nests in below-ground burrows or at ground level. Nests may be lined with shredded paper, cloth, or other fibrous material.
Litters of 6 to 12 young are born 21 to 23 days after conception. Newborn rats are naked and their eyes are closed, but they grow rapidly, eating solid food at 2 1/2 to 3 weeks. They become completely independent at about 3 to 4 weeks and reach reproductive maturity at 3 months of age, sometimes as early as 8 weeks.
Female Norway rats may come into heat every 4 or 5 days, and they may mate within a day
after a litter is born.
When eliminating Norway rats, remember that glue boards are not very effective on large rodents. Snap traps and live traps will work. The most effective control method for these rats is the use of weather proof bait blocks. For more information on control of Norway rats: