Roof rat (Rattus rattus) & Norway rat (Rattus norvegicus)

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Roof rat

Important facts


Refer to the field identification guide for a summary of distinguishing characteristics between the Norway rat, the roof rat and the house mouse. The Norway rat (also called the brown rat, house rat, sewer rat, and wharf rat) and the roof rat (also called the black rat, ship rat, and Alexandrine rat) look very much alike but there are noticeable differences. In general:

  • A Norway rat looks sturdier than the roof rat; the roof rat is sleeker.
  • A mature Norway rat is 2 percent longer than a roof rat, and weighs twice as much.
  • A Norway rat’s tail is shorter than the length of its head and tail combined; a roof rat’s tail is longer than its head and tail.
  • A Norway rat’s ears are small, covered with short hairs and cannot be pulled over the eyes; a roof rat’s ears are large, nearly hairless, and can be pulled over the eyes.
  • A Norway rat’s snout is blunt; the roof rat’s snout is pointed.

Habits of Rats


The pest control applicator must have a thorough under-standing of rats in order to carry out an effective control program. A mature female rat can give birth to about 20 young in a year (4 to 6 at a time). However, the average life span of a rat is less than 1 year, with females having the longest life expectancy. The young are born in a nest and by 3 weeks, they are imitating their mother. Young rats learn from their mother; this innate ability can make control difficult for the pest control applicator. At three months, the young are independent and able to mate.

1 Social Behaviour

Rats are social animals and live in colonies with well defined territories. Each colony has a complex social hierarchy. Rats are aggressive with females being very protective of their young and their nest.

2 Senses of Rats

-Rats have poor vision. They are nearly color blind and react to shapes and movement rather than identifying objects by sight. Their eyes are adapted to dim light. -Rats have an excellent sense of smell and they use their long whiskers and guard hairs as guides through their numerous runways. They have a keen sense of hearing as well as taste -Rats have an excellent sense of balance which allows them to walk on wires and always land on their feet in a fall.

3 Fear of New Objects (Neophobia)

Rats are wary of anything new in their territory. Until they become familiar with an object, they will avoid it; even then rats use extreme caution. When using poison baits, if the poison only succeeds in making the rat ill, they will avoid similar baits in the future.

4 Food and Water

-Norway rats prefer protein-based foods such as meat, fish, insects, pet food, nuts and grain. Household garbage is ideal food for the Norway rat. – Roof rats prefer plant materials such as fruits, nuts, seeds, berries, vegetables and tree bark. They occasionally feed on garbage and meats. If their preferred foods are not available, both rat species will feed on any food that is available. Rats tend to hoard food. Water is required by rats on a daily basis.

5 Range

Rats usually begin foraging just after dark. Most of their food gathering occurs between dusk and midnight but they can exhibit active moments anytime, night or day. Rats commonly travel 30 to 45 m (100 to 150 feet) from their nest looking for food and water.

6 Nesting

Outdoors :

Norway rats tend to nest in burrows dug in the ground. The burrows are shallow and usually short with a central nest. There are extra exits used for emergency escapes. The nest openings are hidden under grass, boards or are plugged with dirt. Roof rats commonly nest above ground in trees, in piles of wood or debris, vine-covered fences and stacked lumber

Indoors :

Norway rats build their nests inside walls, in spaces between floors and ceilings, underneath equipment, between and under pallets, and in crawl spaces, storage rooms or any other cluttered area that is typically unoccupied. Norway rats prefer to build nests in the lower floors of a building.

Roof rats prefer to nest in the upper floors of a building in the attic and in attic or ceiling voids near the roof line. At some times, they will nest in lower levels of a building, as do Norway rats. Both species also nest in sewers and storm drains. They may have more than one nest also.



Rats provide many signs that they are infesting an area. An inspection will identify if an area is infested, and will identify where the rats are feeding and nesting, their pat-terns of movement, and the size of the population. By carrying out an inspection of an area, the pest control applicator will be better able to decide what control methods touse, and where and when to use them. Use a flashlight just after dark to determine signs of infestations, old or new. As well, listen for sounds such as clawing or gnawing which will indicate the presence of rats. Other signs to look for in an inspection are listed below.

1 Droppings

A single rat may produce 50 droppings daily. Roof rat droppings are normally smaller than thoseof the Norway rat. The highest number of droppings will be found in areas where rats are feeding or nesting. Determine if a rat population is active by sweeping up the old droppings and reinserting for new droppings a week later. The appearance of the droppings will also help in determining if the rats are currently active. Fresh rat drop-pings are black or nearly black, they may glisten and look wet and they have the consistency of putty. Week old drop-pings become dry, hard and appear dull. After a few weeks, droppings become grey, dusty and crumble easily.

2 Urine

Both wet and dry urine stains will glow blue-white under an ultraviolet light (black light).

3 Grease Marks

Oil and dirt rub off a rat’s coat as it scrambles along. The grease marks build up in frequented runways and are noticeable. Look along wall/floor junctions, on pipes and ceiling joists or at regularly used openings for grease marks.

4 Runways

Rats constantly travel the same paths. Look for well-polished trails that are free of dust. Runways inside are harder to detect than those outside.

5 Tracks

A rat’s foot print may show four or five toes. They may also leave a “tail-drag” in the middle of their tracks. Look in dust or soft, moist soil for tracks. The use of a tracking patch in suspected runways or near grease marks is a useful tool for finding tracks. (A tracking patch consists of a light dusting powder, such as unscented talc. Don’t use flour which may attract insect pests.) Note: a tracking patch is not the same as tracking powder and is not to be used in the same fashion. Tracking. powder is a rodenticide in the dust form.

6 Gnawing Damage

As a rat’s incisor teeth grow substantially in a year, they keep their teeth worn down by working them against each other as well as gnawing on hard surfaces. Look for gnawing damage by inspecting floor joists, ceiling joists, door corners, kitchen cabinets and around pipes in floors and walls.

7 Odor

Heavy infestations have a distinctive odor which can be identified with practice. The odor of rats can be distinguished from the odor of mice.

Health Hazards


Rats are responsible for the spread of many diseases. Some times they transmit diseases directly, by contaminating food with their urine or feces. Or they can transmit disease indirectly, for example a flea first biting an infected rat, then a person. Some important diseases associated with rats:

1 Plague

The “Great Plague” which killed large numbers of people in Europe is transmitted to people by the oriental rat flea.. The disease The flea bites an infected rat and then, feeding on the human, inoculates them with the bacteria that causes the disease. Although no major outbreak of plague has occurred since the 1920’s, there is still a danger.

2 Murine Typhus Fever This is a relatively mild disease in humans. Murine typhus is transmitted from rats to humans by a rat flea. The disease organism enters the blood stream when faeces of infected fleas are scratched into a flea-bite wound.


3 Rat-Bite Fever

Rats are known to bite humans. A small percentage of peoplebitten by rats can develop rat-bite fever. The bacteria that causes the disease is carried in the teeth and gums of many rats. Although the disease exhibits mild symptoms similar tothe flu, it can be fatal. It is of particular risk to infants.

4 Salmonella Poisoning

Rats frequent areas where Salmonella bacteria thrive, such as sewers and rotting garbage. The bacteria can also thrive in arat’s intestinal tract. If rat droppings end up in food preparation areas, on food, dishes or silverware, Salmonella food poisoning may occur. 5 Leptospirosis or Weil’s Disease This disease is seldom fatal to humans. The disease organ-isms are spread from rat urine into water or food and enter humans through mucous membranes or minute cuts and abrasions of the skin.

6 Trichinosis

Trichinosis results from a nematode, or tiny roundworm, that invades intestines and muscle tissue. Both people and rats can get the disease from eating raw or undercooked pork infected with the nematode. Rats aid in the spread of trichinosis when pigs eat food or garbage contaminated with infested rat droppings.

7 Rabies

Rats have never been found to be infected with rabies in nature. There has been no evidence that rabies are transmitted from rats to humans.

Estimating Rat Numbers


It’s not easy to tell how many rats are infesting a site. As a rough guide, you can use rat signs to characterize the population as low, medium, or high. In rat-free or low infestation conditions, no signs are seen. The area either has no rats or was invaded recently by a few.

With medium infestation, old droppings and gnawing can be observed. One or more rats are seen at night; no rats are seen during the day. When there is a high infestation, fresh droppings, tracks, and gnawing are common. Three or more rats are seen at night; rats may be seen in the daytime.

Control and Management

Most successful rat control programs use a combination of tools and procedures to knock down the rat population, and to keep it down. Methods used combine habitat alteration and pesticide application. Some of the tools, such as baiting and trapping, are lethal to the rat. Some tools are not; rat-proofing, for example. Sometimes applicators recommend changes that their customers need to make, such as increasing the frequency of garbage pickup or making building repairs. The following sections describe some of the major techniques and tools used in controlling rats:

1 Sanitation Food.

Like all animals, rats need food to survive. Baiting programs often fail because the bait can’t compete with the rats’ regular food. The rats simply ignore the baits or cache them. Reducing the rats’ normal food encourages them to feed on any rodenticide baits placed in their territory.

  • Close or repair dumpsters and garbage containers that are left open or damaged.
  • Clean food spills. Do not allow food to be left out overnight.
  • Outdoors, remove seeds spilled under bird feeders or food around doghouses.
  • In warehouses and food plants, look for spills around railroad tracks and loading docks. Ensure food in storage is rotated properly (first in, first out) and is stored on pallets, not on the ground or against walls. The pallets should be 18-24 inches from side walls and placed so that aisles permit inspection and cleaning around the stored food.

2 Eliminate hiding places.


Remove plant ground covers such as ivy near buildings.
Remove high grass, weeds, wood piles, and construction debris that permit rats to live and hide adjacent to a building.


Reduce clutter in rarely-used rooms — basements, storage rooms, equipment rooms. Organize storage areas.

3 Rat-Proofing (Exclusion)

Long term, the most successful form of rat control is to build them out. Also called rat-proofing, this technique makes it impossible for rats to get into a building or an area of a building. Rat proofing prevents new rats from reinfesting a building once it has been cleared.

Building Exterior.

  • Seal cracks and holes in building foundations and exterior walls.
  • Block openings around water and sewer pipes, electric lines, air vents, and telephone wires.
  • Screen air vents. Caulk and seal doors to ensure a tight fit, especially between door and floor threshold.
  • Fit windows and screens tightly. Caulk and close openings on upper floors and the roof, inspect under siding and repair damaged soffits.
  • Repair breaks in the foundation below ground level. Building Interior.
  • Seal spaces inside hollow block voids or behind wallboard. Repair broken blocks and holes around pipes. Repair gnaw holes or stuff them with copper wool.
  • Equip floor drains with sturdy metal grates held firmly in place.


4 Traps


4-1 Snap Trap.

The snap trap is an effective method of killing rats when used correctly. Trapping is advised for use in places where rodenticides are considered too risky or aren’t working well, if the odor of dead rats in wall or ceiling voids would be unacceptable, or when there are only a few rats infesting a limited area. Trapping has several advantages. There is less non-target risk than from a toxicant. The technician knows instantly whether or not the trap has been successful. Traps also allow for disposal of the carcass so that there are no odor problems. Careful attention to detail is necessary to ensure proper placement in adequate numbers or rats will simply pass them by. The best traps are those with expanded triggers (treadles) set for a light touch.

  • Leaving the traps unset for a few days may increase the catch by reducing the chance that wary rats will trip the traps without capture. Set traps with bait, if food for rats is in short supply, or without bait if food is plentiful.
  • Good baits for Norway rats include peanut butter, hot dog slices, bacon, or nut meats.
  • Roof rats respond to dried fruits and nuts, or fresh fruits such as banana or apple. Tie moveable bait to the trigger using string or dental floss, or else the rat may simply remove the bait without triggering the trap.
  • Sprinkle cereal, such as oatmeal, around traps to make them more attractive. Set unbaited traps along runways, along walls, behind objects, in dark corners where the rat is forced through a narrow opening. Place the trigger side of the trap next to the wall. [Rats will step on the trap during their regular travels.]
  • When runways are located on rafters and pipes, set expanded trigger traps directly across them, fastening them to pipes with wire, heavy rubber bands, or hose clamps, and to rafters with nails.
  • Set traps where droppings, gnawing damage, grease marks and other evidence of activity is found.
  • Use enough traps [A dozen may be needed for a house, a hundred for a small warehouse.] Set five or ten traps in an active corner of a room. Set three traps in a row so a rat, leaping over the first, will be caught in the second or third. If unsure about sites of activity, set traps along possible runways spaced 10 to 20 feet apart.
  • Camouflage traps when left with only a few rats that become very difficult to capture. Set traps in a shallow pan of meal, sawdust, or grain. [Place a small piece of cloth or plastic over the trigger to prevent the meal from jamming the mechanism.]
  • In stubborn cases, expose food in shallow pans until the rats readily feed on it. Then add a buried trap. Move boxes and objects around to create narrow runways to the traps.
  • Avoid spraying insecticide on the trap, or even storing traps with application equipment. The odor of other rats improves a trap’s effectiveness. Likewise, the odor of insecticide can make a rat steer clear. Inspect traps frequently to remove dead rodents and change old bait.


4-2 Glue Boards.

Another way to trap rats is with glue boards. Glue boards use a sticky material that captures rodents. Although most often used against mice, they are sometimes effective againstrats. Be sure to use larger glue boards that have been designed to trap an animal the size of a rat. Be aware that some consider glue boards inhumane, since they often kill the rodents.

  • Place glue boards in the same location as you would place snap traps. Place them lengthwise flush along the wall, box, or other object that edges a runway. Overhead runways along pipes, beams, rafters, and ledges are good sites too. Do not place glue boards directly over food products or food preparation areas.
  • Secure the glue board with a nail or wire so a rat can’t drag it away.
  • Install glue boards in bait stations if people might be upset to observe a struggling rat, where children or pets could come in contact with the glue, or in areas with excessive dust or moisture.
  • Check glue boards frequently and dispose of rodents humanly.
  • Adding a dab of bait to the center of the glue board may improve its effectiveness.

5 Rodenticides

A rodenticide is a pesticide designed to kill rodents. There are four major formulations of rodenticides used to control rats: food baits, water baits, tracking powders and fumigants.

5-1 Food Baits.

Rat baits combine a poison effective against rats with a food bait attractive to rats. At one time, applicators mixed their own baits. Now baits are mostly purchased ready-made and packaged as extruded pellets, in a dry meal, or molded into paraffin blocks for wet sites. Baits may be obtained in 45-pound bulk tubs, in place packs containing less than one ounce of bait, or anything in between. Some baits kill rats after a single feeding, some require multiple feedings.

Some are anticoagulants [causing rats to bleed to death], some affect respiration, and others have totally different modes of action. Some are only slightly toxic to people or pets, some moderately toxic, and some very toxic. Several general guidelines should be followed when using a poison bait. First and foremost, protect children, pets, wildlife, and domestic animals from eating the bait. All rodenticides have warnings on the label telling the applicator to place the bait “in locations not accessible to children, pets, wildlife, and domestic animals, or place in tamper-proof bait boxes.”

5-2 Bait boxes.

A tamper-proof bait box is designed so that a child or pet cannot get to the bait inside, but the rat can. [Bait trays and flimsy plastic or cardboard stations are not tamper-proof bait boxes.] Tamper-proof boxes differ in the type and quality of construction, but they are usually metal or heavy plastic. Rat bait stations are normally larger than those used for mice. Most designs are not considered to be truly tamper-proof unless they can be secured to the floor, wall, or ground.

  • Ensure that bait boxes are clearly labeled with a precautionary statement.
  • Check stations or boxes periodically to ensure rats are taking the bait and that the bait is fresh. [Rats will rarely feed on bait that has spoiled.
  • Bait boxes should be placed wherever the rats are most active as determined by droppings and other signs (near burrows, along walls, and at other travel sites, etc.).
  • Put place packs in burrows, in wall voids, and similar protected sites. If a site is damp, use paraffin bait blocks or other water-resistant formulations. Roof rats often need to be baited in areas above ground such as attics, trees, and roofs.
  • Put out enough bait and check it often. [Incomplete baiting can lead to bait shyness and make control difficult.
  • Be sure to limit the rats’ normal food supply or your baits may be rejected.
  • Remember that rats fear new objects at first so that your baits may not be taken for a few days or a week.
  • Once bait is taken, leave the box in place for some time; the rats now consider it to be part of their normal surroundings.
  • Good bait placements can be effective even when placed 15 to 50 feet apart. Bait placed outdoors around a commercial building can kill rats that are moving in from nearby areas.

5-3 Water baits.

Rats drink water daily if they can. When rat water supplies are short, water baits — specially formulated rodenticides that are mixed with water — can be extremely effective. Several types of liquid dispensers are available. The best are custom designed for toxic water baits, but plastic chick-founts can also be used in protected sites. Use water baits only where no other animals or children can get to them.

5-4 Tracking Powders.

Rats groom themselves by licking their fur. Tracking powder makes use of this behavior. This formulation is a rodenticide carried on a talc or powdery clay, applied into areas where rats live and travel. The powder sticks to the rats’ feet and fur, and is swallowed when the rats groom themselves. The major advantage to tracking powders is that it can kill rats even when food and water is plentiful, or if rats have become bait or trap shy. Apply tracking powders more heavily than an insecticide dust [but never deeper than 1/8-inch.] Best application sites are inside wall voids, around rub marks, along pipe and conduit runs, and in dry burrows (when permitted by label). Apply with a hand bulb, bellows duster, or with a (properly labeled) flour sifter or salt and pepper shaker. Do not use tracking powders in suspended ceilings, around air ventilators, or near food or food preparation areas. The powder can become airborne and drift into nontarget areas. [The rodenticide in tracking powders is generally 5 to 40 times more concentrated than that in baits.] Tracking powders can be made with acute poisons or slower acting poisons.