Rats. Debbie Ducommum

people with the same amount of affection and interaction. As the popularity of companion rats began to grow in the United States, especially in California, membership in rat and rodent clubs began to climb, and pet shops reported selling more and more rats as pets. In some areas of the country, rats have become more popular than hamsters.

      The roof rat is the more common wild rat in warm climates and coastal regions.

      Natural History of the Rat

      Rats are members of the rodentia (i.e., rodent) order. There are more than 1,700 species of rodents, making up more than 40 percent of all the world’s mammals. Without a doubt, the rat is far more intelligent than most of its relatives. The only rodent possibly smarter than the rat is the squirrel.

      Rats groom themselves constantly and are actually clean animals.

      Although there are many different rat species, most people think about the two species of wild rats that choose to live near humans. The smaller species of these two rats is the roof rat, Rattus rattus, which is also called the black, ship, or tree rat. The roof rat is thought to have originated in India, making its way around the world with human travelers. Its large ears, long tail, and delicate build are better adapted to tropical climates. It was the first species to have reached Europe, with bones found in ancient sites dating back to the third century A.D.

      The larger and more common rat is the Norway rat, Rattus norvegicus, also known as the brown, common, house, wharf, sewer, and barn rat. The Norway rat is the ancestor of the domestic rat. This rat is thought to have originated in Russia near the Caspian Sea and followed human travelers around the world. The English mistakenly named it the Norway rat because they thought it had arrived on ships from Norway. This rat has small ears, a heavy build, and is suited to cool climates.

       This rat is puffing out his fur and arching his back as a warning.

      The roof rat was the first species to colonize America, with the Norway rat arriving later, in about 1775. In the United States, the roof rat is most common along the coasts, in the South, and in California, while the Norway rat is widespread throughout the rest of the country. In Canada and England, the Norway rat is the dominant species, with the roof rat surviving in some ports and islands.

      While the roof rat and the Norway rat are closely related, they cannot interbreed. In some areas, the two species can live harmoniously, with the Norway rat occupying sewers, basements, and burrows, and the roof rat living in trees and attics. In many cases, however, the Norway rat, a larger and more aggressive animal, has forced the roof rat to move out. Both species have probably always chosen to live near people where they can benefit from our food and shelter.

      Wild rats can do a lot of damage to human property. They gnaw on buildings, wires, and water pipes, and they eat or soil large amounts of food. They can also carry disease. The roof rat was the carrier of the fleas that caused the great plagues of medieval Europe.

      Humans have waged war on rats for centuries, first attacking with dogs, ferrets, and cats, and then with traps and poisons. The most effective way to eliminate wild rats, however, is to remove food sources and prevent rats’ entries into buildings. One study in Baltimore found that cleaning up the streets and alleys of trash reduced the rat population by 50 to 75 percent.

      The wild Norway rat is an adaptable opportunist, able to take advantage of changing conditions. With a tough and athletic compact body, the Norway rat is a good climber, digger, jumper, and swimmer. A slender Norway rat can squeeze her body through any opening big enough for her head, scale a brick wall, leap 4 feet, use utility cables as tightropes, and chew through lead and concrete. The average wild Norway rat weighs only 10 to 17 ounces, although the largest on record was 23 inches long and weighed 2 pounds, 12 ounces.

      In cities, wild rats claim small territories: basements, sewers, and walls of buildings. In the country, they live in or under buildings or in fields, and they may range widely looking for food. Their burrows, which can be up to 4 feet deep, can have three to five entrances, an emergency exit, and many rooms. There are rooms for sleeping, food storage, and latrines. Rats line their nesting chambers with soft material and make bigger, more elaborate nests in cold weather.

      Rats live in large family groups, or colonies, all sharing the same burrow and defending their territory against strangers. All the rats share in the construction of their burrow. Although they’re not true pack rats, Norway rats carry a variety of items to their burrow.

      These hand-raised wild rat pups are just opening their eyes and learning to eat solid food.

      Patchwork hairless rats have short hair that grows in, falls out, and then grows in other places. They can look a little different each week.

      This lynx-colored rat is odd-eyed.

      A Rat’s Life

      Rats are born hairless and blind, totally dependent on their mothers. The average litter size for wild rats is eight. The babies, called pups, nurse for about six weeks, although they start eating solid food when their eyes open at fourteen days. Wild rats reach sexual maturity at two to four months of age. When a female comes in heat, the males do not fight over her but take turns mating with her. The gestation period is twenty-one to twenty-three days. Each mother tends to have her own nesting chamber, although more than one rat may share a nest. Babies learn what foods to eat by taking pieces from adults.

      Rats are omnivorous. Wild rats eat plants, seeds, grains, nuts, fruit, insects, worms, eggs, and carrion. Rats are predatory and catch and kill reptiles, amphibians, fish, birds, and small mammals such as mice. Rats search for food both alone and in groups.

      Although wild rats eat almost everything, they are wary of unfamiliar foods. A rat nibbles only a little of a strange food at first. If it makes her sick, she avoids that food from then on. Rats also avoid foods with a bitter flavor. Since they are unable to vomit, rats must be careful about what they eat.

      The teeth and jaws of a rat, like those of all rodents, are specially designed for gnawing. The four incisors, a pair on the top and on the bottom, are like chisels. They grow constantly throughout a rat’s life to replace the worn-down enamel. A rat also has twelve tiny molars used to chew food. Between the incisors and molars is a space called the diastema where special cheek folds prevent debris from entering the mouth while the rat is gnawing.

      Because we see wild rats eating our garbage, they have the reputation of being dirty animals. They really are quite clean though, grooming constantly by licking themselves and then licking their hands to wash their faces. They also use their back toenails as combs.

      Rats communicate with each other through scent, sound, touch, and visual signals. Vision is their weakest sense. They are mostly color-blind and nearsighted, although they see movement extremely well and can see in very dim light. Some domestic rats weave their heads from side to side to improve depth perception and to help them focus on stationary objects. Rats who do this may be especially nearsighted.

       Rats, like this Berkshire (front) and agouti (back), are social creatures.

      Rats have excellent