Identification, Facts, & Control
12-3/4" to 18" Brown on back and sides with gray
The Norway Rat (Rattus norvegicus), is commonly called barn, house, sewer, wharf, brown, or burrowing rat. Its color is usually brown on back and sides with gray to yellow-white belly. The Norway Rat's Tail shorter than combined length of head and body, lighter colored on the under side. Its body is broad and heavy with blunt muzzle. This rats ears are small, close set, appearing half buried in fur, covered with short, fine hair. The Feet have four toes on front paws and five on back toes. The hind foot is usually longer than 1 1/2" from heel to longest toe. The females usually have 12 mammary glands. The Norway Rat's teeth have no notch on inside of upper front (incisor) teeth. They Weight 10 to 17 ounces and have a length (tip of nose to end of tail) 12-3/4" to 18".
Norway Rat females breed when they are about three months old. The gestation period is about 25 days and litters normally range from 6 to 14 young and average about 8. The litters are usually spaced at intervals of 60 to 65 days. In nature, few rats live more than two years. The first two months are spent in the nest and in short forays with the mother rat. Rats are most active from the third through the ninth month of life. Thereafter activity gradually declines until approximately 18 months of age. Rats older than 18 months are quite inactive.
Norway Rat senses are the same as most rodents.
- Sight: Apparently motion is quickly detected, depth perception is good, and variations in light
intensity are recognized. Other details of vision are probably relatively poor.
- Smell: Sense of smell is very well developed.
- Taste: Sense of taste is probably not as well defined as it is in man.
- Hearing: Hearing is well developed; sources of sounds are accurately located.
- Touch: Sense of touch is quite highly developed. Vibrissae (long stiff hairs extending from the nose) are sensitive feelers on which the rodent relies for contact with its surroundings. Active hairs distributed through-out the fur serve a similar purpose. The nose is very sensitive to touch and is carefully protected.
- Balance: Sense of balance is very well developed.
Food & Water Habits
- Gnawing: Rat incisor teeth are very efficient cutting tools. Rats must gnaw to keep the incisor teeth, which grow about five inches per year, short enough to be useful. They can gnaw through lead pipes, fresh concrete, soft and semi-hardened aluminum and other relatively hard materials.
- Jumping: Norway Rats can jump vertically up to three feet from a standing start, and easily three feet with a running approach and supplemental push against the obstacle. Jumping out and down from a standstill, a rat can cover a horizontal distance of 3 feet while dropping less than 15 feet; it can fall as much as 50 feet without being killed.
- Reaching: Rats can reach from one vantage point to another horizontally along a smooth vertical wall over a distance almost as long as their bodies. Vertical reach is almost the same.
- Climbing: Rats can climb both vertical and horizontal wires, the inside of a vertical pipe with a diameter of from l 1/2 to 4 inches, the outside of a vertical pipe of any diameter if the pipe is within 3 inches of a wall or other continuous support.
- Burrowing: Norway rats have been found to bury as much as five or six feet to reach food.
- Swimming: Rats are excellent swimmers and will readily enter water if it is necessary to obtain an objective.
Rats develop regular habits in eating. They transport their food to harborage for consumption
when possible. Individual colonies often demonstrate a food preference. Rats require 3/4 to 1 ounce of dry food per 24 hour period. Their maximum drive to obtain food
occurs after three or four days of starvation. Norway rats show more preference for meats than other rats. Rats require about one ounce of water per 24 hour period. Maximum drive to obtain water occurs after 1 or 2 days of thirst.
Rats are very cautious and will avoid strange objects as much as possible for several
days. Familiar objects which have been moved will be avoided for a short period and then approached with great caution.
Rats build nests wherever security, food, and water are available. Preferred harborages include enclosed spaces between walls and floors, under counters, machinery, shelving, stairways, etc., in trash piles and in burrows; for nesting and shelter purposes, burrows seldom exceed 18 inches in depth. Nests are well hidden and are rarely found in a routine inspection. They are made of soft, warm materials, such as paper, excelsior, etc.
Rats are primarily nocturnal foragers, but will move about during the daylight under
pressure of hunger, thirst, fear, or anger. They will also be active during the daylight
hours if their fears of men and predatory animals have been allayed by previously
Home ranges of rats depend on a number of factors such as the nearness of food and .
water to places of harborage, quantity of food and water available, presence or absence of
hazards, etc. Experiments conducted in Baltimore indicate that the normal home range is
about 40 feet and rarely exceeds 100 feet. Mice range over a smaller distance from their
homes than do rats, usually not more than 20 feet.
Rats are inclined to establish regular routes which are as well protected as possible.
They will make every effort to maintain contact with a vertical surface through their
vibassae on one side and preferable on both sides.
Mass migrations sometimes occur, presumably caused by crop failures, floods, etc.
Rats are excellent swimmers. They have been known to swim rivers and have been
observed in open water far from shore. Young rats placed in a tank of water will dive
repeatedly in search of an exit. They will sometimes come through the water seats of
toilets in floor drains.
How To Control Norway Rats
Rats have behavioral traits such as aversion to new objects and sometimes having many
alternatives to multiple food sources, that make baiting programs sometimes ineffective.
One should consider pre-baiting traps at the beginning of a control program.
The most common place to set traps in any type of structure is along the walls, especially behind storage bins. Always place traps with the trigger end towards the wall. Place traps at least 6-10 feet apart and always use a sufficient amount of bait in the traps, so that the rats will consume a lethal dose. Always use locked, tamper resistant bait stations in a residence. Monitor the consumption of rodent bait taken in bait stations at least weekly and relocating them after three weeks if there are no signs of acceptance.
Sanitation and exclusion are non—chemical types of control measures. Sealing all small holes or entrances to a structure along with trimming back excess foliage is a good start to control by exclusion. After a rodent control program has been established, the elimination of harborages should be sought in order to maintain treatment effectiveness.
Signs of Norway Rat Infestation
Other Norway Rat Control Information:
- Droppings: Droppings are the most constant and earliest observed signs of infestation. Number, freshness, and size of droppings indicate the extent of the infestation. Droppings are found in secluded corners, harborages, and runways.
- Tracks: Tracks are distinctive and easily recognized; they resemble hand prints. The back feet
have five toes and the front have four. Tail marks appear as wavy lines on dusty surfaces.
- Runways: Rat bodies are dirty and greasy and repeated contacts with surfaces along which they
travel produces smudges. Semi-circular "swing" marks appear under beams and rafters
which obstruct overhead runways.
- Gnawings: Rats gnaw to gain access to food and harborage, and to shorten their incisor teeth. Fresh
gnawings on wood can be distinguished by the light color of the newly exposed wood.
The extent of the damage from gnawing gives an indication of the degree of the
infestation. Also, rubber shavings found during an inspection are the result of rat gnawings.
- Burrows: Burrows are easily observed along the walls of buildings, in dirt floors of buildings,
embankments, fills, under bushes and brush, etc.
- Other Signs: Other signs of rat infestation less frequently observed include urine stains, the use of a
black light will highlight the urine tracks to show rodent pathways. Observation of live
rats in the daytime and the presence of a rat odor are indications of a large rat population.
Dead rats usually indicate that poison has been used or an epizootic has occurred.
Click on a species of rodents below to learn further information.
- Sometimes rat droppings are confused for bat droppings. Bat droppings are thicker and have blunted ends. Bat droppings have a foul odor and can easily be crushed
- The best way to describe the fresh fecal droppings of a rat is that they are glistening and soft.
- A current rodent infestation is characterized by hard droppings, tracks, and a sweet musty odor.
- If a homeowner notices a strong musty, urine—type odor near the bathtub and finds blunt droppings measuring 1/2"-3/4" he is describing evidence that a Norway rat is nesting under the tub.
- A Norway rat will travel 50 to 150 feet from its nest to forage for food and water.
- In order to trap rodents the logical progression is to do an inspection, sanitize the facility, rodent proof the area, and then set traps.
- The average size of an adult Norway rat fecal dropping is 3/4" with blunted ends.
- Traps for rodents should be placed in rodent runways and the owner should be consulted for bait preference.
- When placing snap traps for rats in a warehouse you should use a large number of unset traps initially so the rats get used to the new objects.
- Roof rat activity in a warehouse where signs of grease marks or smudges on the beams are visible should be controlled by affixing rodent bait stations on top of the beams.
- Perhaps the most ineffective place to place traps would be in a location where there are constant mechanical vibrations and noises.
- Tamper-resistant bait stations should be placed in any location in the structure for controlling rodents with the exception of locations near pets and children.
- Patching all the entry points of a structure would be a good integrated pest management measure to take following a rat treatment in a residence.
- An effective method of excluding rats from a structure is to cover all entry points with 1/8" wire mesh. All openings of 1/2" or greater should be sealed with medium steel wool and mortar around pipes.
- Black lights are used to reveal rodent urine during the inspection of commercial buildings.
- If a consumer complains of hearing rodents in walls and attic areas two weeks after a home has been treated for rodents, the decline of bait consumption would indicate the need for a follow up treatment.
- Anticoagulant rodenticides affect a rodent by interruption of clotting ability.
- Zinc phosphate is a good rodenticide to use that acts as an acute poison.
- Bait stations for rats should be placed every 30 feet.
- An effective way to monitor the consumption of rodent bait placed in stations is by checking once per week and relocating bait after three weeks if undisturbed. ·
- Rodenticides should be removed after the termination of the service.
- It is crucial that rodent baits are kept away from any exposure to non-target species.