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The Problem With Rats


The Problem With Rats
Gary Alpert, Harvard University, Bugwood.org
The Problem With Rats

Two species of rodents are most common in the U.S.: 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.

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.

Identification: What Do Rats Look Like?

The Norway Rat (rattus norvegicus)

  • General - large and bulky
  • Body color - coarse brown fur
  • Belly color - gray to grayish 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 and have no fur
  • Location - found across the U.S.
  • Droppings - 3/4-inch long
  • Fun fact - The Norway rat is not really from Norway, rather they are believed to have originated in China.

The Roof rat (Rattus rattus)

  • general - sleek and slimmer than the Norway rat
  • Body color - light black to black fur
  • Belly color - off white to gray
  • Weight - 5 to 9 ounces
  • Length - about 14.5 inches long
  • Tail - hairless and longer than the combined length if 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 - 1/4-1/2-inch long
  • Fun fact - Roof rats are often found high in trees and homes: thus its name.

Signs: 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. For this reason, 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.
  • 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 and these can cause numerous problems, including the decreasing the stability of homes and buildings when they dig beneath them, blocking of sewer lines when nearby, and spoiling the look of landscaping of yards.
  • As climbers, roof rats are more likely to cause structural damage in homes as they chew on wood and wires. They can also reduce harvest as they will climb trees and feed on the fruit.


Rats can spread disease through biting or contact with their fecal matter, or droppings. The most common diseases transmitted to humans or animals by rats are:

Preventing Rats From Making a Home in Your Home

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: 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.

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