Scratching, squeaking, squealing and squabbling, roof rats (Rattus rattus) boldly announce their presence in buildings they inhabit. Scurrying across rafters, nesting in attics and sneaking into kitchens for midnight snacks, these highly adaptable disease-carriers strike terror in the hearts of homeowners. Their equally unwelcome relatives, Norway rats (Rattus norvegicus), patrol basements and lower levels of buildings, sewers and subways. Thus, a difference between roof rats and Norway rats is habitat preference, in addition to variations in physical appearance and behavioral characteristics.
Generally identified by color, three sub-species of roof rats are known: the black rat (Rattus rattus Linnaeus) is black with a gray belly; the Alexandrine rat (Rattus alexandrines Geoffroy) is brown with gray streaks, also known as agouti, with a gray belly; and the fruit rat (Rattus frugivorus Rafinesque) has an agouti back and white belly. In addition to their common names, they are variously called; Old English rats, house rats, gray-bellied rats, white-bellied rats and ship rats.
Norway rats are primarily brown or reddish-gray with whitish-gray bellies. They are also known as brown rats, sewer rats, gray rats, wharf rats, common rats, street rats, water rats, house rats, Hanover rats, brown Norway rats, Norwegian rats and hood rats.
Size and Physical Characteristics
Slender and graceful-looking, roof rats have 7-1/2-inch- to 10-inch-long tails, equal to or a little longer than the length of their combined heads and bodies. Large,floppy ears and pointed muzzles easily distinguish them from Norway rats. Generally moving in whip-like motions, their tails are the same color, top and underside. Their hind feet are about 1.3-inches-long, and overall they range from 13¾ inches to 17¾-inches, and weigh 8 to 12 ounces. Female roof rats have 10 teats,
Norway rats have heavy, thick bodies, blunt muzzles and small, close-set ears. Their 6-inch to 8-1/2-inch tails are dark on top with lighter undersides. Conspicuously shorter than their combined head and body, their tails are carried with comparatively less movement than roof rats'. Their hind feet are about 1.7 inches long; overall they range from 12¾ inches to 18 inches, and weigh from 10 to 17 ounces. Female Norway rats have 12 teats.
Range and Habitat
Both species were unintentionally introduced to North America and throughout the world in the 1700s by European seafarers traveling on rat-infested ships. Roof rats live in trees or vine-covered fences, landscaped residential and industrial areas, parks with ponds or reservoirs, riverbanks and streams. More widely distributed than roof rats, Norway rats burrow into the ground along streams and rivers, under buildings and in garbage dumps. A common pest on farms, they inhabit barns, granaries, livestock buildings, chicken houses, silos and kennels.
Roof rats are expert climbers and gain access to buildings by climbing onto roofs from trees or overhead utility lines. Faster and more agile than Norway rats, they use their tails for balance on electrical wires, much like squirrels. Norway rats are excellent swimmers who readily dive through water seals in toilets, emerging in toilet bowls. Although they can climb, they’re not nearly as adept as roof rats, and prefer traveling over flat surfaces. They enter buildings at the foundation or below the ground level.
Food Habits and Preferences
Omnivorous, roof rats and Norway rats eat a wide variety of foods, but each species has its own preferences. Outdoors-living rats of both species seek food outside if it’s available. Otherwise, they may enter homes and other buildings at night, returning to their burrows after feeding. Others nest and spend their whole lives inside, partaking of a wide range of foods. Roof rats prefer seeds, fresh vegetables and fruit, vegetative parts of native and ornamental plants, wheat and corn. Norway rats prefer a diet rich in carbohydrates and proteins: livestock feed, fresh fruits and vegetables, meat, sugar, flower bulbs, corn flour, wheat, beans, bread, even injured rats may be eaten.
- Rat Behavior: Norway Rat and Roof Rat Quiz
- Rat Behavior: Wild Rats Lifespan
- University of California Agriculture and Natural Resources: Rats
- Scientific Guide to Pest Control Operations, Purdue University; Lee C. Truman, Ph.D. et al
- Animal Diversity Web: Roof Rats
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