Rats are some of the most troublesome and damaging rodents in households. They consume and contaminate food, damage structures and property, transmit parasites and diseases to other animals and humans. Rats live and thrive under a wide variety of climates and conditions; they are often found in and around homes and other buildings, farms, gardens, and open fields.
Norway Rats (Rattus norvegicus)
Rattus norvegicus is a rather large member of the mouse family. On average, these rats reach nearly 400mm nose-to-tail, and weigh 140gm to 500gm. Males are usually larger than females.
In natural populations, these rats are covered with coarse, brownish fur (sometimes splotched with black or white hairs) on their dorsal surface, which usually lightens to a grey or tan colour nearing the underside.
Various strains of these rats bred in captivity may be white, brown, or black. The ears and tail are bald. The length of the tail is shorter than the length of the body. Molars are lophodont and the dentary is 1/1-0/0-0/0-3/3. The ears of Norway rats are typically shorter than those of related species, and do not cover up the eyes when pulled down.
The mating system of R. norvegicus is best described as polygynandrous. Social animals,
Norway rats tend to breed in large groups. Once a female enters her six-hour oestrus period, she may mate as many as five-hundred times with competing males.
The maximum lifespan of R. norvegicus is 4 years (in captivity). In the wild, it is assumed that they live for upwards of 2 years.
Rats, like house mice, are mostly active at night. They have poor eyesight, but they make up for this with their keen senses of hearing, smell, taste, and touch. Rats constantly explore and learn about their environment, memorizing the locations of pathways, obstacles, food and water, shelter, and other elements in their domain.
They quickly detect and tend to avoid new objects placed into a familiar environment. Thus, objects such as traps and baits often are avoided for several days or more following their initial placement. While both species exhibit this avoidance of new objects, it is usually more pronounced in roof rats than in Norway rats.
Both Norway and roof rats may gain entry to structures by gnawing, climbing, jumping, or swimming through sewers and entering through the toilet or broken drains. While Norway rats are more powerful swimmers, roof rats are more agile and are better climbers.
Norway and roof rats do not get along. The Norway rat is larger and the more dominant species; it will kill a roof rat in a fight. When the two species occupy the same building, Norway rats will dominate the basement and ground floors, with roof rats occupying the attic or second and third floors. Contrary to some conceptions, the two species cannot interbreed. Both species may share some of the same food resources but do not feed side-by-side. Rats may grab food and carry it off to feed elsewhere.
Rats of either species, especially young rats, can squeeze beneath a door with only a 1.25cm gap. If the door is made of wood, the rat may gnaw to enlarge the gap, but this may not be necessary.
HOW TO SPOT RAT INFESTATION
Because rats are active throughout the year, periodically check for signs of their presence. Once rats have invaded your garden or landscaping, unless your house is truly rodent proof, it is only a matter of time before you find evidence of them indoors.
Experience has shown it is less time consuming to control rodents before their numbers get too high, and fewer traps and less bait will be required if control is started early.
Inspect your yard and home thoroughly. If the answer to any of the following questions is yes, you may have a rat problem.
|–||Do you find rat droppings around dog or cat dishes or pet food storage containers?|
|–||Do you hear noises coming from the attic just after dusk?|
|–||Have you found remnants of rat nests when dismantling your firewood stack?|
|–||Does your dog or cat bring home dead rat carcasses?|
|–||Is there evidence rodents are feeding on fruit/nuts that are in or falling from the trees in your yard?|
|–||Do you see burrows among plants or damaged vegetables when working in the garden?|
|–||Do you see rats travelling along utility lines or on the tops of fences at dusk or soon after?|
|–||Have you found rat nests behind boxes or in drawers in the garage?|
|–||Are there smudge marks caused by the rats rubbing their fur against beams, rafters, pipes, and walls?|
|–||Do you see burrows beneath your compost pile or beneath the garbage can?|
|–||Are there rat or mouse droppings in your recycle bins?|
|–||Have you ever had to remove a drowned rat from your swimming pool or hot tub?|
|–||Do you see evidence of something digging under your garden tool shed or doghouse?|
DAMAGE CAUSED BY RATS
Rats consume and contaminate foodstuffs and animal feed. They also damage containers and packaging materials in which foods and feed are stored. Both species of rats cause problems by gnawing on electrical wires and wooden structures (doors, ledges, in corners, and in wall material) and tearing up insulation in walls and ceilings for nesting.
Norway rats may undermine building foundations and slabs with their burrowing activities. They may also gnaw on all types of materials, including soft metals such as copper and lead as well as plastic and wood. If roof rats are living in the attic of a residence, they can cause considerable damage with their gnawing and nest-building activities. They also damage garden crops and ornamental plantings.
Among the diseases rats may transmit to humans or livestock are murine typhus, leptospirosis, trichinosis, salmonellosis (food poisoning), and ratbite fever. Plague is a disease that can be carried by both roof and Norway rats, but in California it is more commonly associated with ground squirrels, chipmunks, and native wood rats.
MANAGING RAT PROBLEM
Three elements are necessary for a successful rat management program: sanitation measures, building construction and rodent proofing, and, if necessary, population control.
Sanitation is fundamental to rat control and must be continuous. If sanitation measures are not properly maintained, the benefits of other measures will be lost, and rats will quickly return.
Good housekeeping in and around buildings will reduce available shelter and food sources for Norway and, to some extent, roof rats. Neat, off-the-ground storage of pipes, lumber, firewood, crates, boxes, gardening equipment, and other household goods will help reduce the suitability of the area for rats and will also make their detection easier.
Garbage, trash, and garden debris should be collected frequently, and all garbage receptacles should have tight-fitting covers. Where dogs are kept and fed outdoors, rats may become a problem if there is a ready supply of dog food. Feed your pet only the amount of food it will eat at a feeding, and store pet food in rodent-proof containers.
Building Construction & Rodent Proofing
The most successful and long lasting form of rat control in buildings is to “build them out.” Seal cracks and openings in building foundations, and any openings for water pipes, electric wires, sewer pipes, drain spouts, and vents. No hole larger than 6mm should be left unsealed to exclude both rats and house mice.
Make sure doors, windows, and screens fit tightly. Their edges can be covered with sheet metal if gnawing is a problem. Because rats (and house mice) are excellent climbers, openings above ground level must also be plugged. Rodent proofing against roof rats usually requires more time to find entry points than for Norway rats because of their greater climbing ability. Roof rats often enter buildings at the roof line area so be sure that all access points in the roof are sealed. If roof rats are travelling on overhead utility wires, contact a pest control professional or the utility company for information and assistance with measures that can be taken to prevent this.
Rodent Proofing Your Home
|–||Repair or replace damaged ventilation screen around the foundation and under eaves.|
|–||Provide a tight fitting cover for the crawl space.|
|–||Seal all openings around pipes, cables, and wires that enter through walls or the foundation.|
|–||Be sure all windows that can be opened are screened and that the screens are in good condition.|
|–||Cover all chimneys with a spark arrester.|
|–||Make sure internal screens on roof and attic air vents are in good repair.|
|–||Cover rooftop plumbing vent pipes in excess of 2 inches in diameter with screens over their tops.|
|–||Make sure all exterior doors are tight fitting and weatherproofed at the bottom.|
|–||Seal gaps beneath garage doors with a gasket or weather stripping.|
|–||Install self-closing exits or screening to clothes dryer vents to the outside.|
|–||Remember that pet doors into the house or garage provide an easy entrance for rodents.|
|–||Keep side doors to the garage closed, especially at night.|
|–||Population control – When food, water, and shelter are available, rat populations can reproduce and grow quickly. While the most permanent form of control is to limit food, water, shelter, and access to buildings, direct population control is often necessary.For controlling rats indoors, use traps. Baiting is best done outdoors only, otherwise rats may die behind a wall. In hot weather, the stench of a dead rat can be unbearable and may necessitate cutting a hole in the wall to remove the carcass. Also, ectoparasites such as fleas and mites often leave dead rat carcasses and may infest the entire house if the carcass is not removed promptly.|
Trapping is the safest and most effective method for controlling rats in and around homes, garages, and other structures as traps can be used over and over again. Traps can be set and left indefinitely in areas where rats have been a problem in the past, such as an attic.
The kind of bait used for the trap is important. Nut meat, dried fruit, or bacon make excellent baits for rats. The bait should be fastened securely to the trigger of the trap with light string, thread, or fine wire so the rodent will spring the trap in attempting to remove the food. The best places to set traps are in secluded areas where rats are likely to travel and seek shelter. Droppings, gnawings, and damage indicate the presence of rodents, and areas where such evidence is found are usually the best places to set traps, especially when these areas are located between their nests and food sources. Place traps in natural travel ways, such as along walls, so the rodents will pass directly over the trigger of the trap. If a rat sets off a trap without getting caught, it will be very difficult to catch the rat with a trap again.
One of the alternatives to a snap trap is a glue board. Glue boards work on the same principle as flypaper: when a rat or mouse attempts to cross the glue board, the rodent gets stuck. Glue boards are much more effective for mice than for rats. Also, one of the major drawbacks with glue boards (and other live-catch type traps) is that the trapped rat may not die quickly, and you will need to kill it. For this reason, glue boards are not a good alternative for many people and their use is not recommended. Also, cats and dogs may get into the glue and track it around the house, creating additional problems.
Live traps are not recommended because trapped rats must either be killed or released elsewhere. Releasing rats outdoors is not recommended because of health concerns to people, pets, and other domestic animals. Because neither the roof nor Norway rat is native to this country, their presence in the wild is very detrimental to native ecosystems. They have been known to decimate some bird populations.
While trapping is generally recommended for controlling rats indoors, when the number of rats around a building is high, you may need to use toxic baits to achieve adequate control, especially if there is a continuous reinfestation from surrounding areas. If this is the case, consider hiring a licensed pest control applicator, who is trained to use rodenticides safely.
Bait stations or boxes are often used with baits of all kinds. These enclosures protect the bait from weather and restrict accessibility to rodents, providing a safeguard for people, pets, and other animals. Bait stations should be large enough to accommodate several rats at a time and should contain a bait-holding compartment. Each station should have at least two openings for rats to enter and exit.
Place bait stations next to walls or in places where rats will encounter them. Commercial bait stations are available in a variety of sizes and shapes. Stations that may be accessible to children or pets must be made of sturdy, tamper-resistant material and be secured in a way that they cannot be tipped. See the product label for additional information. All bait stations should be clearly labelled.