Common Name: Norway Rat
Latin Name: Rattus norvegicus
Common Family Name: Rats and Mice
Latin Family Name: Muridae
Other Names: Brown rat, ship rat, wharf rat, sewer rat, gray rat, barn rat, burrowing rat, water rat, common rat, house rat, migratory rat, wander-rat
What are Norway Rats?: Norway Rat (Rattus norvegicus) Is also known as the Brown Rat. These rats are larger than Roof Rats, with a more robust body, slightly longer, but a bit shorter tail. They can weigh up to a pound. They are more common in northern parts of the country. They are more likely to live at ground level, like below a house, or in the basement, but can inhabit any part of a building.Both types of rats have excellent hearing and sense of smell, but poor eyesight. They often travel via urine or pheromone pathways. They have excellent speed and balance, and can easily climb most surfaces. They seek out shelter in safe places, and they also seek out warmth and food, and that’s why you’ll often find rats in buildings.
Origin: Evolved in Central Asia, but reached Europe in the 1700’s, the United States later that century, and now it is found throughout the world. It is a rodent of cooler climates, but now also infests many tropical environments as well, primarily in the seaport areas.
Biology: This rat is commonly sold as a “pet rat”, and has been bred for white coloration as “lab rats” as well, leading to the occurrence of white and brown marked races. It is primarily a ground dweller, although it can climb very well, and prefers to reside in burrows. It swims very well and often lives in sewers and other underground water systems. It is primarily a nocturnal animal, and will restrict its range of movement only to that which is needed to find food and water, perhaps only 20 or 30 from home. Norway Rats are omnivores and opportunistic feeders, feeding on any natural or human foods available. They are neophobic and may avoid new objects placed in their environment for some time. A normal life expectancy for them is one year or less, although when cared for they may live several years. The gestation period of the female is 22 days, litters average 8 to 9 pups, and she may have several litters in her one year. Damage from gnawing can be extensive, as they chew on pipes of plastic or metal, wires, wood, or furnishings and walls, and commonly bite humans. While not the primary reservoir of bubonic plague, they have the potential to spread this disease, along with several others as well as filth infections.
Identification: Adult rats are large and robust, being up to 16 inches from nose to tip of tail. Their tail length is shorter than their body length, and it is scaly and almost without hairs. Colors range from white to brown to mottled, or blackish gray, reddish brown, and other variations. In relation to its head it has a blunt nose, small eyes, and small ears.
Characteristics Important in Control: Habitat modification to eliminate harborage sites is effective, along with proper building maintenance to exclude their entry. Elimination of available interior and exterior food and water supplies is needed. Burrows may be treated by fumigation in some circumstances, and the use of traps and baiting are highly effective. The shyness these rats exhibit toward new objects can affect the response to bait boxes and traps. Glue trays may not be highly effective due to the strength of this species, and its ability to pull free from the glue. Like the other domestic rodents they prefer to remain against vertical surfaces, in contact with their “guard hairs” on their body, and control measures should be placed against these pathways.
The brown rat, common rat, sewer rat, Hanover rat, Norway rat, Brown 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, with rare exceptions (see below) the brown rat lives wherever humans live, particularly in urban areas.
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 550 g (19 oz) in males and about 350 g (12 oz) in females, but a very large individual can reach 900 g (32 oz). Brown rats have acute hearing, are sensitive to ultrasound, and possess a very highly developed olfactory sense . The vision of a pigmented rat is poor. The brown rat is usually active at night and is a good swimmer, both on the surface and underwater, but unlike the related Black Rat (Rattus rattus) they are poor climbers. Brown rats dig well, and often excavate extensive burrow systems. A 2007 study found brown rats to possess metacognition, a mental ability previously only found in humans and some primates.
The brown rat is a true omnivore and will consume almost anything, but cereals form a substantial part of its diet. The brown rat can breed throughout the year if conditions are suitable, a female producing up to five litters a year. The gestation period is only 21 days and litters can number up to fourteen, although seven is common. Brown rats live in large hierarchical groups, either in burrows or subsurface places such as sewers and cellars. When food is in short supply, the rats lower in social order are the first to die. If a large fraction of a rat population is exterminated, the remaining rats will increase their reproductive rate, and quickly restore the old population level. Rats are known to burrow extensively, both in the wild and in captivity, if given access to a suitable substrate. Rats generally begin a new burrow adjacent to an object or structure, as this provides a sturdy “roof” for the section of the burrow nearest to the ground’s surface. Burrows usually develop to eventually include multiple levels of tunnels, as well as a secondary entrance. Older male rats will generally not burrow, while young males and females will burrow. Similar to other rodents, brown rats may carry a number of pathogens which can result in disease, 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 cause Q fever, with seroprevalence for the bacteria found to be as high as 53% in some wild population.