The roof rat (Rattus rattus) is one of two introduced rats found in the contiguous 48 states. The Norway rat (R. norvegicus) is the other species and is better known because of its wide-spread distribution. A third rat species, the Polynesian rat (R. exulans) is present in the Hawaiian Islands but not on the mainland. Rattus rattus is commonly known as the roof rat, black rat, and ship rat. Roof rats were common on early sailing ships and apparently arrived in North America by that route. This rat has a long history as a carrier of plague.
Three subspecies have been named, and these are generally identified by their fur color: (1) the black rat (R. rattus rattus Linnaeus) is black with a gray belly; (2) the Alexandrine rat (R. rattus alexandrinus Geoffroy) has an agouti (brownish streaked with gray) back and gray belly; and (3) the fruit rat (R. rattus frugivorus Rafinesque), has an agouti back and white belly. The reliability of using coloration to identify the subspecies is questionable, and little significance can be attributed to subspecies differentiations. In some areas the subspecies are not distinct because more than one subspecies has probably been introduced and cross-breeding among them is a common occurrence. Roof rats cannot, however, cross with Norway rats or any native rodent species.
Roof rats are not protected by law and can be controlled any time with mechanical or chemical methods. Pesticides must be registered for rat control by federal and/or state authorities and used in accordance with label directions.
Roof rats, also called black rats, have soft, smooth brown fur with black intermixed. The underside (abdominal area) may be white, gray, or black. Roof rats’ bodies are 6 to 8 inches long with a 6- to 8-inch scaled tail, for a total of about 16 inches. Weight is about 5 to 9 ounces, but may reach 12 ounces.
Roof rats range along the lower half of the East Coast and throughout the Gulf States upward into Arkansas. They also exist all along the Pacific Coast and are found on the Hawaiian Islands. The roof rat is more at home in warm climates, and apparently less adaptable, than the Norway rat, which is why it has not spread throughout the country. Its worldwide geographic distribution suggests that it is much more suited to tropical and semitropical climates. In rare instances, isolated populations are found in areas not within their normal distribution range in the United States. Most of the states in the US interior are free of roof rats, but isolated infestations, probably stemming from infested cargo shipments, can occur.
Tracks and Signs
Droppings of roof rats are about 1/2 inch long with pointed ends.
Information on this species is based on the chapter in Prevention and Control of Wildlife Damage (Hygnstrom, Larson, Timm, ed. 1994), written by Rex Marsh (Specialist in Vertebrate Ecology, University of California, Davis).