Norway Rat Facts & How to Get Rid of the Rodents

General Information

What is a Norway rat?

Also known as brown rats or sewer rats, Norway rats live on every continent in the world except Antarctica. The widespread rodents are the species of pest rat most commonly found in the United States, where the vermin tend to inhabit urban and suburban neighborhoods like those established throughout New England. Scientifically named Rattus norvegicus, Norway rats frequently live among humans in populated areas where sources of food and water are plentiful. The common name, Norway rat, stems from the rodent first entering Europe on Norwegian ships in the middle of the 16th century. Norway rats successfully occupy all populated regions of the world by reproducing regularly, adapting easily to a wide range of environments and climate zones, and displacing indigenous rodent species of smaller size. An infestation of Norway rats can cause property damage, contamination of food, and the transmission of various diseases to humans and pets.

Also Read :Rat Exterminator

Appearance & Identification

What does a Norway rat look like?

Larger than mice and most other rats found in New England, the Norway rat boasts an average length of nearly 16 inches, which includes the tail. The rodents are stocky relative to mice and weigh as much as a pound when fully grown. Males typically grow larger than females. The head of the Norway rat is characterized by small ears, tiny eyes, and a blunt nose. The rats are covered in coarse, dark fur that transitions in color to gray or white on the underside of the rodents. The layer of fur does not extend to the ears or tail which remain hairless. Newborn Norway rats are completely bald and only begin growing fur at about two weeks of age.

Also Read :Rat Control

Habits/Habitat

Highly adaptable, Norway rats inhabit a variety of different environments ranging from fields and woodlands to dumpsters and sewers. The rodents also reside in the basements of New England homes, particularly in spaces where garbage is permitted to accumulate. Natural burrowers, Norway rats often establish outdoor nests beneath trash heaps, woodpiles, and the concrete foundations of buildings. Indoors, the pest rodents live in wall voids as well as areas cluttered with undisturbed debris such as storage spaces. Norway rats tend to nest in close proximity to each other and form live in groups that function according to a clearly defined hierarchy. The rodents are nocturnal creatures that emerge at dusk to dig burrows, construct nests, and search for food.

Diet

What do Norway rats eat?

Like other omnivores, Norway rats adhere to a varied diet largely composed of proteins and carbohydrates like meats and grains. In urban and indoor areas, the foraging rodents primarily subsist on the remnants of food items discarded by humans. Norway rats also feed on seeds and nuts, fruit, leaves and roots, and even other animals like birds, fish, and mice. The omnivorous rodents boast the ability to consume roughly a third of their body weight in food in a single day and travel up to 150 feet from the nest when foraging.

Also Read : How To Get Rid Of Rats

Reproduction

Prolific breeders, Norway rats mate throughout the year, with periods of increased breeding activity typically occurring during the warmer months. After a gestation period of about three weeks, mated females give birth to litters of eight to 12 offspring. Norway rats are born with closed eyes and hairless bodies. The eyes of newborn Norway rats open after two weeks, which is also the approximate length of time it takes the rodents to grow fur. Weaning takes place at three to four weeks of age, with newly weaned Norway rats leaving the nest about five weeks after birth. The rodents achieve sexual maturity and can begin mating at an age of three or four months. Sexually mature Norway rats retain the ability to breed for two years and produce up to seven litters annually.

Problems Caused by Norway Rats

The presence of Norway rats poses several threats to people, pets, and property. Norway rats living in indoor environments can spread salmonellosis and contaminate food consumed by humans. The rodents also facilitate the transmission of serious diseases like hantavirus, jaundice, plague, and rat bite fever. Norway rats frequently serve as host animals for fleas and lice, as well. Property damage occurs when the pest rodents gnaw through the pipes, wiring, furnishings, and foundations of homes. In fact, rats are estimated to cause an annual total of roughly $1 billion in property damage across the United States.

Signs of a Norway Rat Infestation

Wary of strangers and nocturnal by nature, Norway rats tend to remain out of sight during daytime hours. Nevertheless, the rodents often leave behind telltale signs of their presence. Evidence of a Norway rat infestation includes droppings, which typically measure between one-half and three-fourths of an inch long. The gnawing rodents may also leave holes or teeth marks in objects made of plaster, plastic, soft metal, and wood. Other indicators of an infestation include footprints and runways created by the tendency of Norway rats to travel the same path when outside the nest. Norway rats living within wall voids often produce audible squeaking noises and gnawing sounds.

Prevention

New England residents can prevent Norway rat infestations by storing food securely, cleaning up spills thoroughly, disposing garbage properly, and removing piles of debris from around their home or building. Homeowners should also seal any holes around and keep outdoor vegetation away from the structural foundation of indoor structures to eliminate cover/harborage for foraging Norway rats. Severe infestations often prove difficult to handle and frequently require the services of a pest control professional with experience in dealing with Norway rats.

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Ecology & Behavior of Roof Rats

Like Norway rats and native rats, roof rats are nocturnal (active at night). The most significant behavioral difference between the species, which has implications for control methods, is the aerial nature of roof rats. Roof rats prefer to forage for food above ground in elevated areas indoors and outdoors. They are agile climbers and travel through trees and along vines, wires, rafters, and rooftops. They often use trees and utility lines to reach food and to enter buildings, but can also be found foraging in dense ground cover. Like Norway rats, roof rats can swim and may use sewer systems to disperse to new areas.

Roof rats may nest in your neighbor’s yard but find food in your yard. Outdoors, they can travel several hundred feet in a single night to find their survival resources. They prefer to nest in secluded areas above ground in such places as attics, soffits, overhead garage storage, in the vine cover of fences or buildings, and in wood piles or other stored materials where harborage can be found. They favor dense non-deciduous trees or trees with hollow cavities and the crowns of palm trees, especially when old fronds are not removed. Roof rats sometime burrow in the ground especially in hot, dry environments. In these areas, they may use trees, materials stored on the ground, concrete slabs and sidewalks to support shallow

burrows.

Roof rats have a high reproductive potential and may breed year-round in warmer areas. Females produce 5 to 8 pups per litter with a possible 4 to 5 litters per year.

Food Habits

Roof rats are omnivores (plant- and animal-eating). They are very fond of fruit, especially oranges (Figure 2). In addition to citrus they will feed on fruit-producing ornamentals, dates, stored food, birdseed in feeders, insects, snails, and garbage. These rats will also feed on stored food and livestock feed and will contaminate much more than they actually eat. They obtain much of their water requirement from their food, but unless their diet includes a sufficient amount of succulent plant material,they will require a source of free water such as landscape irrigation.

Roof rats generally begin searching for food shortly after sunset. These rats may cache or hoard considerable amounts of solid food, which they will eat later. These food caches may be located in attics, in dense vegetation such as hedges, or in a variety of other hiding places generally near their nests.

Roof Rat Signs

Roof rat signs include smudge marks on surfaces from oil and dirt rubbing off their fur as they travel (Figure 3). Because of their propensity to climb, look for these smudges up high on structures, e.g. between rafters, as opposed to marks along walls near the floor which could be made by other rodent species. Because they are often living overhead, between floors or above false ceilings, there is less tendency to see signs of roof rat tracks, urine, and droppings.

Source: The University of Arizona Cooperative Extension