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Rats also have eaten bait and died in buildings, leaving a distinct odor. Their fleas, ticks and mites spread disease.

Rat trapping, control and removal

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Norway Rats Under Deck - © Harbor Wildlife Control
Norway Rats Under Deck - © Harbor Wildlife Control

The roof rat (R. rattus) or black rat is one of two introduced rats found in the contiguous 48 states. The Norway rat (R. norvegicus) is the other species and is better known because of its widespread distribution. A third rat species, the Polynesian rat (R. exulans) is present in the Hawaiian Islands but not on the mainland. Roof rats were common on early sailing ships and apparently arrived in North America by that route. This rat has a long history as a carrier of plague.

Norway Rat
The brown rat, common rat, Hanover rat, Norway rat, Norwegian rat, or wharf rat (Rattus norvegicus) is one of the best known and most common rats. One of the largest muroids, it is a brown or grey rodent with a body up to 25 cm (10 in) long, and a similar tail length; the male weighs on average 350 g (12 oz) and the female 250 g (9 oz). Thought to have originated in northern China, this rodent has now spread to all continents, except Antarctica, and is the dominant rat in Europe and much of North America—making it the most successful mammal on the planet after humans. Indeed, the Norway rat lives wherever humans live, particularly in urban areas.

Norway rats carry some diseases, including Weil's disease, rat bite fever, cryptosporidiosis, Viral hemorrhagic fever (VHF), Q fever and hantavirus pulmonary syndrome. In the United Kingdom, brown rats are an important reservoir for Coxiella burnetii, the bacteria that causes Q fever, with seroprevalence for the bacteria found to be as high as 53% in some wild populations.

Range of Rats in the US
Norway and Roof Rat Range

The fur is coarse and usually brown or dark grey, while the underparts are lighter grey or brown. The length can be up to 25 cm (10 in), with the tail a further 25 cm (10 in), the same length as the body. Adult body weight averages 350 g (12 oz) in males and about 250 g (9 oz) in females, but a very large individual can reach 500 g (18 oz). Rats weighing over 1 kg (2.2 lb) are exceptional, and stories of rats as big as cats are exaggerations, or misidentifications of other rodents such as the coypu and muskrat.

Norway rats have acute hearing, are sensitive to ultrasound, and possess a very highly developed olfactory sense (smell). Their average heart rate is 300 to 400 beats per minute, with a respiratory rate of around 100 per minute. The vision of a pigmented rat is poor, around 20/600, while a non-pigmented (albino) with no melanin in its eyes has both around 20/1200 vision and a terrible scattering of light within its vision. Brown rats are dichromates who perceive colours rather like a human with red-green colorblindness, and their colour saturation may be quite faint. Their blue perception, however, also has UV perceptors, allowing them to see ultraviolet lights that some species cannot.

Captured Norway Rat - © Harbor Wildlife Control
Captured Norway Rat ©HWC

Roof Rat
The roof rat's scientific name is Rattus rattus. Historically, they are associated with having spread the plague or black death during the Middle Ages. The roof rat is also known as the black rat, even though it is not necessarily black in color, but rather is usually dark brown. Your typical roof rat is between 13 to 18 inches long, including its tail. In fact, it is distinguished from other rats by that tail, which is longer than the rest of its body. Roof rats are sleek, slender, and agile. Their have large ears.

Roof rats also have an excellent sense of balance. They use their tails for balance while traveling along overhead utility lines. They move faster than Norway rats and are very agile climbers, which enables them to quickly escape predators. Their keen sense of hearing also aids in their ability to detect and escape danger.

Control Methods

Traps
Trapping is an effective method of control. It is the preferred method in homes, garages and other structures where only a few rats are present. Trapping has several advantages: 1) it does not rely on inherently hazardous poisons; 2) it permits the user to determine if the rat was killed and 3) it allows for disposal of rat carcasses, thus eliminating odor problems that may occur when poisoning is done within buildings. However, trapping is useless if the procedures to prevent reinfestation are not followed.

Exclusion, Sanitation
“Excluding” rodents and trapping are the most effective control methods. Rodent baits should be used only to supplement these methods. If there is a repeated need to use baits, it is likely that sanitation and rodent-proofing should be improved. Remember that rodent baits are poisons. Make sure they are registered with the U.S. Environmental Protection Agency and always follow the label instructions exactly. If baits are used indoors, be sure they are labeled specifically for interior use.

Captured Norway Rat - © Harbor Wildlife Control
Dead Mice in Wall ©HWC
Use of Rodentcides in Home

Poison Baits (Rodenticides)
Rodenticides are poisons that kill rodents. They can be purchased in hardware stores, feed stores, discount stores, garden centers and other places where pesticides are sold. Do not buy unlabeled rodent baits from street vendors or other uncertain sources. Do not purchase baits that have an incomplete label or one that appears to be “homemade.”

Myth: Rats DO NOT go out for water once a bait has been consumed, the poison will kill the animal wherever it has taken effect, this could mean a wall in your home.

Sound and Electronic Devices
Rats quickly become accustomed to regularly repeated sounds. Ultrasonic sounds, those above the range of human hearing, have very limited use because they are directional and do not penetrate behind objects. Also, they quickly lose their intensity with distance. There is little evidence that sound of any type will drive established rats from buildings or otherwise give adequate control. See Rutgers Fact Sheet on Ultrasonic Devices.

Control by Cats and Dogs
Many rat problems around homes can be related to the keeping of pets. In fact, rats may live in very close association with cats and dogs. Rats frequently live beneath a doghouse and soon learn they can feed on the dog's food when he is absent or asleep. Although house cats, some dogs and other predators kill rats, they do not usually provide effective rat control.

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