Information about Rats

rats rattus information about

Rats are medium-sized rodents of the family Muridae. The term “rat”, however, is most generally used in reference to the members of the genus Rattus, the so-called “true rats”. It may also be used in reference to a number of small mammals, which are not rats, such as the North American pack rat or the Kangaroo rat. Rats can be distinguished from mice by size, having longer bodies and longer legs. Interestingly, Ancient Romans did not differentiate between rats and mice; they chose to refer to rats as “mus maximus” (big mouse) and to mice as “mus minimus” (little mouse).

rats rattus information about

There are more than 60 species of rats, including the most important:

  • Rattus argentiventer: rice-field rat;
  • Rattus hoffmanni: Hoffmann’s rat;
  • Rattus lutreolus: Australian swamp rat;
  • Rattus norvegicus: Norway rat, also known as the brown rat or the sewer rat;
  • Rattus osgoodi: Osgood’s Vietnamese rat;
  • Rattus rattus: house rat, also known as the black rat;
  • Rattus xanthurus: Northeastern Xanthurus rat, also known as the Sulawesi white-tailed rat.

The most common species of rats, and the ones that people come in contact with most often, are the black rat (Rattus rattus) and the brown rat (Rattus norvegicus). Due to their often encounters with humans and the damages they can cause these are the ones that are mostly considered pests.

Description and distribution

Rats have long, thin bodies, long legs, and a thin tail. The tail helps them with balance, communication, as well as regulation of body temperature (through constriction and expansion of the blood vessels there). They have eyes, ears, a nose (all of which provide developed senses), and front teeth that grow 11-14cm in each year. As rodents do, rats wear them down by continuously gnawing on everything and anything around them, including cement, wood, lead pipes, as well as other small animals.
Although they are indeed bigger than mice, rats actually come in all sizes. The largest species of rat is the Bosavi wooly rat (which was only recently discovered, in 2009, in the rainforest of Papaua New Guinea, and does not have a scientific name yet), which is about the size of an adult cat: 82cm in length, from nose to tail, and 1,5kg in weight. One of the smallest rats, on the other hand, is Osgood’s Vietnamese rat (Rattus osgoodi), barely measuring 12-17cm. In general, rats seldom weigh more than 500g.

Brown rats can grow up to 30-40cm, and weigh around 200-500g. They are grey on the underside and a reddish or greyish-brown on the top part of the body. Ears and tails are hairless, with the tail measuring less than the rat’s body.
Black rats are smaller than brown rats, and weigh around 140-180g. They are light grey or white on the underside and dark grey or black on the top part of the body. Their tail will be longer than their body.

Rats originated in Asia and Australia and are present on every continent, with the exception of Antarctica, whose hostile climate is too severe to allow them to survive. However, rats have been introduced to many islands near Antarctica. In all of these places, rats are extremely common – so much so that in the United States, statistics claim that there is approximately one rat per person.
Most species are nocturnal, although the brown rat is known to be awake during daytime, as well, especially when the population grows so large that controlling territory and finding food and water become difficult. Depending on the species, as well as on the environment in which they live, rats will have different adaptable characteristics. For example, brown rats are very good swimmers, whereas black rats are very good climbers. Most species have a very well-developed sense of smell, and an excellent memory.

“Home” for a rat will generally be a nest, although where exactly this nest is constructed will depend, again, on the species and the environment. As such, there are 2 types of rat species: terrestrial or arboreal. Black rats, because they are good climbers, often build nests above ground-hence the reason why they are sometimes called “roof rats”. Shrubs, trees, dense vegetation, as well as high cabinets, walls, false ceilings, attics, roofs, etc., are all areas that may be appealing to them. This is not always the case, however; sometimes, they will also build nests in burrows. Brows rats, on the other hand, will build nests exclusively in underground burrows, whether that is along building foundations, under woodpiles, under piles of debris, or in basements or the ground floor of buildings. These nests are where rats mate, raise their younglings, store food, and seek protection from predators. True to their ingenious and opportunistic nature, rats can construct their nests from any combination of material they are able to find, including grass, branches, paper, and trash.

Breeding and dietary information

Rats usually live in groups, called “packs” or “mischiefs”. The group dynamics depend on the species. While brown rats are usually led by the largest male in the group, some species may have several dominant males or females. What is interesting is that rats actually take care of other members of the group, especially if they are ill or injured. Furthermore, without companionship, rats have been observed to become lonely and depressed. When a male and female leave to mate and nest in an area that is not yet claimed, a new group will be formed.
Rats are polygamous, breeding very quickly and very easily. A single female can mate around 500 times in a 6-hour period of receptivity (a state that she experiences around 15 times a year); she is able to mate again only 18 hours after giving birth, and can produce around 7 litters per year. As a result, a single pair of brown rats can produce as many as 2,000 descendants in a single year. Mating generally occurs in the warm months of the year, but not exclusively so. Gestation lasts around 12-16 days. Exactly how many babies a female will have depends on the species; brown rats can have up to 22, while more tropical species usually only have around 6. When they are born, babies weigh only around 6-8g. They grow quickly, though, and by the age of 3 months, they are able to reproduce. Younglings are called pups or kittens.

Predators of rats include: large birds of prey (e.g. owls, hawks, falcons, etc.), as well as various species of snakes. In urban or suburban areas, rats have 2 main enemies: cats and humans.

When threatened, rats become very aggressive; they will fight, bite, and even chase, but this is generally more effective against each other and against small enemies. Otherwise, rats are also very resilient. They are able to swim, can actually tread water for 3 whole days, and can even survive being flushed down the toilet. They can also fall as far down as 15m and still survive. What’s more, they are aided in survival by their suspicious nature: rats are very wary of any novelties introduced into their territories or foraging paths, especially close to their homes, so, often times, they will know in advance when something is wrong and they will hide.
A rat’s average lifespan depends on the species to which it belongs, but most do not live more than a year, due to predation. 2-3 years is usually the maximum that a wild rat can live. Up to 97% of house rats also die within their first year of life.

Most rats are omnivores, with a preference for meat, although some, like the Sulawesi white-tailed rat and Hoffman’s rat, are “vegetarian”, with a preference for vegetation. They are opportunistic feeders, and will eat:

  • vegetation: seeds, grains, fruits;
  • meat: carcasses, insects, snails, mussels, fish, amphibians, reptiles, small birds (e.g. poultry), small mammals (e.g. mice).

Certain species may have certain preferences. The brown rat will eat more foods that are high in protein (e.g. meat scraps, pet food, etc.), while the black rat will generally display a preference for fruit.
Rats that live in urban or suburban areas usually rely on humans as their primary source of food, scavenging through trash or eating any food that is left unprotected. In desperate times, rats are also known to eat their own faeces, seeing as they have nutritional value. Interestingly enough, rats can last more than a camel without water.

Rats as pests

Throughout history, rats have been considered deadly pests, whether it was thought that they helped spread the Bubonic Plague. Nowadays, most urban areas have to deal with rat infestations, these leading to the myth that the rat population in Manhattan equals that of its human population. Rats have the ability to swim up sewer pipes into toilets. Places to look for rat infestations are around pipes, behind walls and near garbage cans. Effective rat control requires municipal workers and individuals to work together.
Harmful for crops, materials and hygiene, rats consume all kinds of foods, they contaminate them with urine, faeces and other secretions and they also produce damage to furniture, electrical wires, shelves, beams, doors and plastic. They also carry a lot of disease that can be transmitted to other animals or even humans. Rats are known for being carriers of fleas, which on their own carry different other diseases, such as Lyssa virus, Salmonella, threadworm and other ecto- and endo-parasites.

Generally, when introduced into locations where they previously did not exist, rats are known to cause a large amount of environmental degradation. The black rat is considered to be one of the world’s most invasive species; it is also known as the ship rat, seeing as it has been carried on vessels, all around the world, the same of which can also be said about the brown rat. Both of these species are omnivorous, and thus capable of eating a wide variety of plant and animal material; therefore, it is no surprise that they have contributed to the extinction of many species of wildlife around the world, such as plants, invertebrates, reptiles, birds, as well as small mammals. Some experts actually believe that between 40% – 60% of all seabird and reptile extinctions (with 90% of them occurring on islands) can be blamed on rats. Due to this devastating effect that they have on native flora and fauna, especially on islands, efforts to eliminate rats are on-going in many parts of the world.

Despite the fear or disgust that they may awaken in some people, rats are also known to be kept as pets. Specially bred rats have actually been used as pets since the late 19th century. They are usually variations of the brown rat, but people have also kept black rats and giant pouched rats (genus Cricetomys). Rats that are bred especially to be pets or rats that have lived as pets from the beginning of their lives behave differently from wild rats; they are calm, friendly, can be taught to perform various behaviours, do not bite, and, most importantly, they do not pose any more of a health risk than a cat or a dog.
It is much more of a generally known fact that rats are used as subjects for scientific research. Their intelligence, adaptability, ingenuity, and aggressiveness are only a couple of the traits that make them popular choices. Over decades, rats have been used in a variety of experimental studies, whose findings have contributed to our understanding of genetics, of diseases, of brain functioning and the effects of drugs, of behaviour, etc. Therefore, we can say that rats have actually provided great benefits to the health and general well-being of the human race.

Furthermore, rats have been used for other, more unusual purposes, as well. For example, their developed sense of smell has been employed by the Belgian non-governmental organization APOPO, which trains rats (specifically African giant pouched rats, also known as Cricetomys gambianus) to detect landmines and diagnose tuberculosis.

Should you be dealing with an infestation with common rats and need to protect your property and crops from them, apply the methods of control suggested in our article about ‘How to get rid of Rats‘. From traps to baits and repellents, find out how you can escape an infestation, but also keep in mind that prevention is as important as exclusion. For ways in which you can ‘Prevent infestation with Rats‘, check our article and learn more about how you can remove attractants and apply repellents in order to keep rats at bay.

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