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Rattus rattus (Linnaeus 1758)

Order Rodentia : Family Muridae

*Introduced species

DESCRIPTION. A blackish (or brownish), medium-sized, slender rat with long, naked, scaly tail; tail usually longer than head and body but not always so; mammae in five or six pairs. Averages for external measurements: total length, 370 mm; tail, 190 mm; hind foot, 36 mm. Weight, up to 200 g.

Rattus rattus

DISTRIBUTION. Common over most of Texas, especially in towns.

HABITS. Black rats, also known as roof rats, are largely commensals and live in close association with humans. They seldom become established as feral animals as do the Norway rats. They inhabit grocery and drug stores, warehouses, feed stores, and poultry houses and can be very common in cotton gins and associated grain warehouses. On farms they live in barns and granaries. They may live near the ground, but usually they frequent attics, rafters, and crossbeams of buildings. They make typical runways along pipes, beams, or wires, up and down studding, or along horizontal ceiling joists, often leaving a dark-colored layer of grease and dirt to mark their travel ways. Like the Norway rat, the black rat is largely nocturnal, and only where populations are relatively high does one see them frequently in the daytime. There is some indication that the larger and more aggressive Norway rat is supplanting the black rat in many parts of the United States. In the southern United States, however, the black rat is by far more common.

They accept a wide variety of food items, including grains, meats, and almost any item that has nutritive value.

Black rats breed throughout the year, with two peaks of production, in February and March and again in May and June. The period of least activity is in July and August. The gestation period is approximately 21 days, and the number of young per litter averages almost seven. At birth, the pups are naked, blind, and nearly helpless. They mature rather rapidly, are weaned when about 3 weeks old, and are able to reproduce when approximately 3 months old. In Texas, young females with a head and body length of 125 mm were sexually mature. Similar to the Norway rat, the black rat is destructive to property and foodstuffs. Also, it plays an important part in the transmission of such human diseases as endemic typhus, rat-bite fever, and bubonic plague.

POPULATION STATUS. Introduced, common. The introduced black rat lives in close association with humans and their structures. It is a pest and can have negative effects on native species of rodents.

CONSERVATION STATUS. The IUCN lists the black rat as a species of least concern, and it does not appear on any federal or state list of concerned species. No conservation is needed.

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From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016.  Courtesy of the University of Texas Press.

Natural Science Research Laboratory