The two rat species that are most common in the United States are the Norway rat and the roof rat. Along with the common house mouse, both rats are believed to have been brought to the U.S. aboard ships bound for the New World in the 17th and 18th centuries.
Both rat species can invade homes and cause problems with their gnawing, feeding, dropping of feces, and ability to carry disease. Following is information on what rats look like, how you know if you have rats in your home, and details on why they are a problem.
While Norway and roof rats are very similar and can be difficult to distinguish on sight, the rats do have some distinctive traits that provide evidence for identification.
The Norway Rat (Rattus Norvegicus)
- Body: Large and bulky
- Fur: Coarse, brown
- Belly color: Gray to grayish, with a brown underbelly
- Weight: 7 to 18 ounces
- Length: About 16 inches long
- Tail: Scaly and shorter than the length of the head and body combined
- Ears: Small with no fur
- Location: Found across the U.S.
- Droppings: 3/4-inch long
- Fun fact: The Norway rat is not really from Norway; they are believed to have originated in China.
The Roof Rat (Rattus Rattus)
- Body: Sleek and slimmer than the Norway rat
- Fur: Light black to black
- Belly color: Off-white to gray
- Weight: 5 to 9 ounces
- Length: About 14 1/2 inches long
- Tail: Hairless and longer than the combined length of its head and body
- Ears: Ears, and eyes, are larger than those of the Norway rat
- Location: Found primarily in the southeastern states and western coastal regions
- Droppings: 1/4 to 1/2-inch long
- Fun fact: Roof rats are often found high in trees and homes: thus its name.
How Do I Know If I Have Rats?
Because rats are nocturnal and are most active at night, an infestation can develop before a rodent is ever seen. So it is best to keep an eye—and an ear—out for signs of rodent presence. These include:
- Live or dead rats.
- Droppings, especially around human or pet food or in or around trash areas.
- Noises in the dark, such as scratching sounds from the attic.
- Nests or piled nesting materials in hidden areas.
- Evidence of gnawing of wires or structural wood.
- Signs of burrows around the yard; under the home or outbuildings; or gnawed fruits in trees.
- Smudge marks along walls or rodent hairs along paths, in nests, or near food.
Why Are Rats a Problem?
- Norway rats dig burrows in which to live. These can cause problems to the stability of homes and buildings when the rats dig beneath them; they also can block sewer lines and spoil the landscaping of yards.
- As climbers, roof rats are most likely to cause structural damage in homes when they chew on wood and wires. They also will climb fruit trees and feed on the fruit.
Rats can spread disease through their biting or human contact with their feces/droppings. The most common diseases transmitted to humans or animals by rats are:
- Rat bite fever
- Murine typhus
Control and Prevention
The best control of any rodent is prevention focused on sanitation and exclusion. In most cases, the reason a rat will enter a home is because it is looking for food, water, or shelter.
- Sanitation: To reduce the availability of food and water, employ sanitation methods such as covering or packaging all foods; keeping all food and food-preparation areas swept, mopped, and wiped clean; keeping trash areas clean, and removing or limiting exposed water.
- Exclusion: To reduce the opportunity for rats that are seeking shelter to enter your home, build out the rodents through rodent-proofing and pest-proofing techniques.