Common Name: Rodent – Norway Rat
Other Names: Brown Rat, Ship Rat, Wharf Rat, Sewer Rat, Gray Rat, Barn Rat, Burrowing Rat, Water Rat, Common Rat, House Rat, Migratory at, Wander-Rat.
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. Norway Rats are omnivores and opportunistic feeders, feeding on any natural or human food 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.