Identification, Facts, & Control

Latin Name

Rattus rattus


Roof Rat.jpg 13-3/4" to 17-3/4" Usualy has some or all black and large ears


The Roof Rat (Rattus (rattus, alexandrinus and frugivorous)) is commonly known as roof, tree, climbing, ship, black, or gray rat. The Rood Rat has a Tail longer than the combined length its head and body, and is uniform color top and bottom. Their Body slender and light with a pointed muzzle. The Roof Rat has its Ears large and prominent, standing well out from fur, with no hairy covering. Its Feet have four toes on the front paws and five on back feet. The hind foot usually less than 1 1/2 inches from the heel to tip of longest toe. The Female Roof Rat has ten mammary glands. They have no notch on inside of their upper front teeth. Roof Rats weight 4 to 12 ounces and are 13-3/4" to 17-3/4" from the tip of nose to end of tail.

The color of the Roof Rat varies depending on the Sub-species and is as follows.
  • Rattus rattus is black to slate colored on both back and belly.
  • Rattus alexandrinus is reddish-brown back with grayish white belly. The hairs on their belly are always slate colored at their bases and never clear white or lemon colored.
  • Rattus frugivorous is gray back with white or lemon colored belly. The hairs on their belly are white or lemon colored at their bases.

Life Cycle

Roof Rat females breed when they are about three months old. The gestation period is about 25 days and litters normally range from 4 to 10 young and average about 6. 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.


Roof Rats 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. Vibrassae (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.

Physical Abilities

  • 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: Roof 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: Roof rats have been found to burrow 2 1/2 feet
  • Swimming: Rats are excellent swimmers and will readily enter water if it is necessary to obtain an objective.

Behavior Patterns

Food & Water Habits
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. Roof Rats show more preference for fruits and vegetables than Norway 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.

Nocturnal Activity
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 undisturbed forays.

Home Range
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.

Travel Routes
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 Roof 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 Roof Rat Infestation

  • 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.

Other Roof Rat Control 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 rat is nesting under the tub.
  • A 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 Roof 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.

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