Rat is a furry mammal that looks like a mouse but is larger. The smallest kinds of rats grow longer and weigh more than the largest mice. Rats, like mice, beavers, and squirrels, are rodents. All such animals have chisellike front teeth suited for gnawing.
There are about 120 species (kinds) of rats. The best known are the black rat and the brown rat. Both these species live in all parts of the world. Most other kinds of rats live in areas not inhabited by people. 
Black rats and brown rats rank among the most serious animal threats to people. They carry the germs of several diseases, including plague, food poisoning, and typhus. Rats also damage or destroy crops and other food products. They kill poultry, lambs, and baby pigs. On the other hand, scientists use rats in research projects that have benefited people.
The word rat is often used for any long-tailed rodent that is larger than a mouse. But most of these animals are not true rats. They include the cotton rat, the rice rat, the kangaroo rat, and the woodrat.
The body of a rat.
All species of rats have a slender, scaly tail. All rats also have long, sharp claws. But black rats and brown rats differ in several ways besides color.
Black rats grow 7 or 8 inches (18 or 20 centimeters) long, not including their tail. They weigh about 10 ounces (280 grams). The tail is longer than the rest of the body. These rats have large ears, a pointed snout, and soft fur. The fur of a black rat may be black, grayish-brown, or smoky-gray. Gray, white, or yellow fur covers the animal’s underside. Black rats are also called roof rats or ship rats.
Brown rats measure from 8 to 10 inches (20 to 25 centimeters) long, not including their tail. They weigh up to 16 ounces (450 grams). The tail is shorter than the rest of the body. Brown rats have small ears, a blunt snout, and coarse fur. They vary in color from brownish-gray to reddish-gray. Other names for the brown rat include barn rat, gray rat, house rat, Norway rat, and sewer rat.
The life of a rat.
Black rats and brown rats originally lived in Asia. They reached Europe by ship or overland. From Europe, they spread to North and South America on ships. More brown rats than black rats live in North America. Some black rats live near coastal seaports in the northern United States. But most dwell in the Gulf states, such as Louisiana and Texas. Brown rats live throughout the United States.
Both black and brown rats live in large groups. Certain rats dominate (have control over) others. Most members of both species build a nest in or near buildings. Black rats live in the upper stories of buildings or in trees. Brown rats are found under floors, within walls, in piles of garbage, or in the ground. If the two species live in the same building, black rats usually occupy the upper levels, and brown rats dwell on the ground level. Rats are cautious. They generally avoid anything unfamiliar in their environment. They have a keen sense of smell and can quickly detect approaching danger.
Both black and brown rats eat almost any kind of plant or animal. They even eat other rats. The brown rat is fierce and aggressive. The black rat is milder. Rats feed mostly at night. Sometimes, they band together and attack such animals as chickens and pigs. Most rats live within an area that may be no more than 150 feet (46 meters) in diameter. But if a food shortage occurs, rats may travel long distances in search of food.
Most black and brown rats mate the year around. The females give birth to three to six litters annually. A female rat carries her young in her body for about three weeks before they are born. Most black rat litters consist of six or seven pups (young). Most brown rat litters have eight or nine pups. Newborn rats are blind and deaf. They remain in the nest for about three weeks.
Few rats live more than a year in their natural surroundings because they have so many enemies. Animals that prey on rats include cats, dogs, hawks, owls, snakes, and weasels. In captivity, some rats live more than three years.
Rats and people.
Rats thrive in farm and city environments, where they cause damage totaling billions of dollars a year. Both black and brown rats destroy eggs, fruits, stored grain, vegetables, and other foods. They also attack various farm animals. Rats also cause additional damage by gnawing on such objects as furniture and lead pipes. They sometimes cause fires by chewing the insulation off electric wires. In addition to spreading disease, rats sometimes attack human beings, including babies in cribs. Their bite may cause a disease called ratbite fever.
Some people fight rats by destroying the food sources or homes of the animals. Others kill rats by poisoning, shooting, or trapping them. Rat poisons must be used carefully to prevent accidental poisoning of other animals.
Rats may also be controlled by placing specially treated food in areas where they live. Such food contains chemicals called antifertility drugs. These drugs make the rats incapable of reproducing.
Domesticated varieties of brown rats, especially the white rat, play an important role in many research projects. Researchers use white rats in studies of disease, drug effects, heredity, nutrition, and learning and other aspects of behavior. They also use rats in the preparation and testing of new drugs. Many zoos maintain colonies of rats as food for snakes and other animals. Some people keep domesticated rats as pets.
