Brown Rat ( Rattus norvegicus )
|Fischer von Waldheim , 1803|
The rats ( Rattus ) are a genus of rodents from the group of old world mice (Murinae). The genus includes around 65 species, most of which are common in Southeast Asia , New Guinea and Australia . In the wake of humans, the brown rat and the house rat in particular have achieved worldwide distribution. From the wild brown rat originated domesticated , kept as a pet pet rat from. In a broader sense, the term rats is unsystematically applied to many other representatives of the old world mice and other rodents.
Rats are a diverse group, the individual species differ considerably. They reach a head body length of 8 to 30 centimeters, the tail length is variable, depending on the species, the tail can be significantly shorter to significantly longer than the body. The brown rat, one of the heaviest species, reaches 200 to 400 grams - individual animals can weigh up to 500 grams. Many species are significantly lighter, with Polynesian rats in Hawaii reaching an average weight of 38 grams.
The fur can be soft or hard, in some species the hair is modified to form spikes. On the upper side, its color varies from black through various gray and brown tones to yellowish and reddish, on the underside it is usually whitish or light gray. The paws and the tail with scale rings are often only sparsely hairy or not at all hairy.
The stomach of rats is divided into two compartments: forestomach and stomach body. The forestomach has a glandless (cutaneous) mucous membrane , the stomach body the usual gastric mucous membrane . Both departments are separated by a fold of the mucous membrane. The esophagus also flows into the stomach in this area. This fold makes vomiting almost impossible for rats. Difficult-to-digest food components are broken down in the large appendix .
Head and teeth
Rats have a pointed snout. The tooth formula is I 1/1 - C 0/0 - P 0/0 - M 3/3, so a total of 16 teeth. As in all rodents, the incisors are transformed into rootless, permanently growing incisor teeth . There is a large gap called the diastema between the incisors and the molars .
In the nose-side corner of the eye is the Harder gland ( haw - gland ) that a porphyrinhaltiges reddish secretions produced. This secretion is distributed when cleaning. In sick animals with a reduced need for cleaning, this secretion accumulates in the corner of the eye or drains through the tear duct to the nostril .
The sense of smell is well developed. It is not only used to search for food, but also plays an important role in communicating with conspecifics. The hearing is also well developed. Like other small rodents, rats hear into the ultrasound range. Located in the inner ear located vestibular system is built complex and very powerful.
distribution and habitat
The original range of the rats comprised Southeast Asia from India and China to the Indonesian islands and extended to New Guinea and Australia . Rats are thus one of the few placentates that have crossed the Wallace line and made their home in the Australian region. Of all land-bound placenta animals, only other Old World mice managed to do this before humans arrived. Today the common rat and the house rat are distributed worldwide, and the Pacific rat has also expanded its range to numerous Pacific islands.
Most rats live in forests. Their habitats can vary from deep rain forests to mountain forests, with most species avoiding human proximity. Some species, however, have adapted to the proximity of humans as cultural followers and can be found in houses as well as in rice fields and other agricultural areas.
Lifestyle and diet
Rats can live on the ground or on trees. Many species can climb well and build nests in the trees for shelter. Others retreat into earthworks, crevices in the rocks or into hollow tree trunks.
The better-researched, culture-following species live in groups of up to 60 animals, whereby the group members recognize each other by their smell. Groups are made up of one or more males and several females; both sexes establish a hierarchy. They are territorial animals, the territories are defended against intruders. Little is known, however, about the way most species live.
Rats are omnivores and eat a wide variety of plant and animal foods. Most species prefer seeds, grains, nuts and fruits, but supplement the menu with insects and other small animals. But there are also species that mainly consume meat. Brown rats, for example, are mainly carnivores; their prey includes birds and their eggs, small mammals and other vertebrates, and also fish. The species that live in the vicinity of humans often find their food in storage facilities, in fields or in garbage. House rats and brown rats can not only eat everything that humans eat, but also additional substances such as fur, soap, paper and beeswax.
Under favorable climatic conditions, reproduction can take place all year round, but there are often fixed mating times. In the dry season from June to October, the New Guinea rats have hardly any litters or no litters, and the Australian rat species also reproduce seasonally: for animals in the south of the continent, the peak of births is in spring and early summer.
The number of litters per year therefore also depends on the climate. With species that reproduce all year round, there can be up to twelve litters a year, with others, however, only one to three. The gestation period is variable, around 21 to 22 days for the house rat and slightly longer for the brown rat. For other species it can vary from 19 to 30 days.
Brown rats can give birth to up to 22 newborns, with an average of eight to nine. In most species, however, there are significantly fewer, so studies of species on the Malay Peninsula revealed three to six newborns and only one to three newborns on New Guinea. Newborn brown rats weigh around five to seven grams at birth and are naked and blind, at fifteen days their eyes open and their fur is present. Young brown rats are weaned at around 22 days and leave their nest.
Brown rats can be sexually mature at two to three months and house rats at three to five months. In other species it takes longer, for example Pacific rats sometimes only reproduce after the first winter.
Rats and humans
Rats in the wake of humans
Of the more than 60 species of rats worldwide, several have largely joined humans and live temporarily or permanently in their environment. These are the Norway rat ( R. norvegicus ), the black rat ( R. rattus ), the Pacific rat ( R. exulans ), the climbing disabled Reisfeld rat ( R. argentiventer ), the Himalayas rat ( R. nitidus ) and the Central Asian rat ( Turkestan rat ) .
The house rats probably only came to Central Europe with the Roman settlement, as the "ship rat" it has expanded its range since ancient times. The brown rat probably did not reach Central Europe until the 18th century. Due to the changed construction of houses and ships, it largely displaced the house rat in the 20th century. The Pacific rat was spread throughout Oceania as the Lapita culture spread.
Rats have reached remote islands through humans and often pose a threat to the native fauna. In particular, brown rats, which eat eggs and young birds as well as small vertebrates, are responsible for the drastic decline or even the extinction of several species.
Rats as pests
The less specialized and therefore very adaptable wild animals are generally considered to be food pests . The damage they cause to agriculture is enormous, so pesticides are used against them . They also occur in gardens, where roots and tubers are particularly gnawed. They also like to use tunnels that have been dug by moles . Buildings are also affected because these rodents can damage water and sewer pipes. The spread of pathogens by rats is also a problem.
Free-living rats, like almost all other animals, can act as vectors directly or indirectly to transmit various pathogens with the diseases they cause. Salmonella , leptospira , streptobacillus moniliformis and hantaviruses are among the more than 70 diseases ( zoonoses ) that can be transmitted to humans . Via the rat flea ( Xenopsylla cheopis ), which through its bite can also infect humans with the bacterium Yersinia pestis , free- living rats can indirectly be carriers of the plague . It is doubted whether the epidemics in antiquity and especially in the Middle Ages in Europe ( Black Death ) were due to rats alone. In addition, rats, along with other small rodents, are reservoir hosts for various types of Borrelia ( bacteria ), which can then be transmitted to animals and humans by vectors such as ticks .
According to the German accident prevention regulations, operators of wastewater systems are obliged to fight rats . This mainly affects the municipalities and wastewater associations. The reason for this regulation is the fight against Weil's disease .
Free-living rats are fought with toxins ( rodenticides ). The toxins developed for rats - especially 4-hydroxycoumarins - impede blood clotting. Other rats avoid eating baits that cause immediate death of the animals.
In archeology, the black rat ( Rattus rattus ) and the brown rat ( Rattus norvegicus ) play a special role in researching the mechanisms of the spread of the medieval plague. In the past, these two rat species were kept as indispensable intermediate hosts for the spread of the plague in Europe. This went so far that researchers inferred the occurrence of rats from the spread of the plague. Since both rat species were native to Europe in the Middle Ages, but only the house rat prefers the proximity to humans necessary for transmission, a distinction between the skeletons of the two species was necessary for the findings of rat bones. They can only be distinguished by the shape of the roof of the skull and the size and shape of the space between the incisors and molars in the lower jaw and the chewing surface of the molars. Since the chewing surfaces shrink with increasing age, this feature is only applicable to young animals. The archaeological finds of the rat species under consideration show that the spread of the plague does not correspond to the rat habitat: In Northern Europe, a rat population was determined for the Middle Ages that was not responsible for the spread of the plague, which has significantly reduced the population in Norway sufficient. The oldest skeleton find of the black rat in Scandinavia dates from the 9th century in Birka. From this, contradicting conclusions were drawn in research: Benedictow postulated that one had not looked for the skeletons in the right place. There must have been a lot more. But he couldn't get his way. The so-called "revisionists" (Shrewsbury, Twigg, Scott / Duncan and Cohn) concluded from the absence of the rat finds that it must have been another epidemic. Other researchers who were able to detect the bacterium Yersinia pestis in the teeth of medieval skeletons concluded from the same finding that the rat was not necessary as an intermediate link, but that there must have been other transmission routes.
Threat to rats
The ubiquity of some rat species should not hide the fact that many rat species are threatened. As with many other animals, island endings are particularly affected. The reasons for this lie in persecution by introduced predators, in hunting and the destruction of their habitat.
Two species found on Christmas Island , the Maclear rat ( Rattus macleari ) and the Christmas Island rat ( Rattus nativitatis ), have become extinct. The IUCN lists seven species as "endangered" ( endangered ): R. burrus , R. hainaldi , R. lugens , R. montanus , R. ranjiniae , R. simalurensis and R. vandeuseni . Seven other species are considered "at risk" ( vulnerable ): R. hoogerwerfi , R. lugens , R. nikenii , R. palmarum , R. richardsoni , satarae R. , R. stoicus and three as ( "low risk" near threatened ) . For 13 species there is “too little data” ( data deficient ). Around half of all rat species are “not at risk” ( least concern ).
Rats in culture
Western culture sees the rat as having negative attributes mainly.
In the fable , rats - in contrast to mice - are considered sneaky, cowardly and cunning. The use as a swear word for people is linked to these properties . In the literature, rats appear as the cause of the worst mental and physical torments, for example in Edgar A. Poe's The Pit and the Pendulum or George Orwell's 1984 . The legend of the Pied Piper of Hameln is well known .
Newer children's books, on the other hand, try to do justice to the rat through a more positive “characterization”. A rat plays a positive role in Kenneth Grahame's book The Wind in the Willows from 1908. The rat is also increasingly valued as a positive figure in international films, for example in the US animated film Ratatouille from 2007, in which an extraordinary rat friendship with closes a young man and helps him find his life.
The Asian and Indian regions, on the other hand, attribute predominantly positive properties to the rat. It serves as a mount for the Hindu god Ganesha and is seen as a symbol of intelligence. In the Karni Mata Temple , thousands of rats are fed by believers; it is considered lucky if one of the “holy” rats runs over the foot of a visitor. In the Chinese zodiac and in general in Chinese astrology , the rat or mouse (鼠, shǔ) takes the first position. A rat stands for honesty and creativity, among other things. In some cultures, the animal is also valued and consumed as rat meat.
Numerous paraphrases in the German language use the word "rat", such as " landlubber ", " rat king " (for a complete mess ), "rat hole" (for a nasty dump) or "rat tail" (for an overly long unpleasant chain of consequences) .
The saying “ The rats are leaving the sinking ship ” is a paraphrase of the fact that rats on board a ship try to get to safety if it threatens to sink, for example because of the holes they have gnawed in the hull. The meaning is transferred to people who are trying to escape from a tricky or dangerous situation that they may have caused themselves when it slowly emerges.
In Luxembourg , the German-speaking areas of Switzerland and Belgium, and in most parts of Germany, “the rat” is the dominant term. In addition, in Franconian and Bavarian , less in the Alemannic language area, often "the Ratz" occurs, in South Tyrol and parts of Austria also "the Ratze".
Wilson & Reeder (2005) list rats as the namesake of the Rattus genus group, a group of Old World mice that is predominantly native to Southeast Asia . This group includes even the genera Luzon-wide-tooth rat ( Abditomys ) bandicoots ( Bandicota ), white-toothed rat ( Berylmys ), Philippines Moss mice ( Bullimus ) bunomys ( Bunomys ), Ryukyu rats ( Diplothrix ) Sody tree rats ( Kadarsanomys ), Komodo rats ( Komodomys ) limnomys , nesokia ( nesokia ), Ceram rats ( Nesoromys ) Palawan rats ( Palawanomys ) papagomys ( papagomys ), Sulawesi-giant rats ( Paruromys ), Flores-long nose rats ( Paulamys ) , Sunda giant rats ( Sundamys ), Taeromys , Tarsomys and Mearns luzon rats ( Tryphomys ). In total, the Rattus group comprises around 110 species.
According to the genetic studies of Lecompte et al. a. (2008) the animals of the Rattus group are part of a radiation of the old world mice, the Rattini, which is mainly found in Southeast Asia, New Guinea and Australia. This radiation also includes the Crunomys group , the Dacnomys group , the Maxomys group and the Micromys group . The Melasmothrix group probably also belongs here.
Wilson & Reeder (2005) divide the genus into 66 species, which are divided into six species groups and some species that do not belong to any group:
- the brown rat ( Rattus norvegicus ) was originally native to East Asia, and in the wake of humans it has spread worldwide.
- the Himalayan rat ( Rattus nitidus ) lives in the Himalayan region and in Southeast Asia.
- the Central Asian rat ( Rattus pyctoris ) (formerly R. turkestanicus or R. rattoides ) occurs in Central Asia and the Himalayan region.
- the Pacific rat ( Rattus exulans ) lives in Southeast Asia and has been introduced to numerous Pacific islands.
- the black rat ( Rattus rattus ) originally lived in Southeast Asia and is now a cosmopolitan worldwide.
- the Indonesian smooth-fur rat ( Rattus adustus ) is only known from one specimen that was found on the Indonesian island of Enggano (south of Sumatra).
- the Indochinese forest rat ( Rattus andamanensis ) inhabits northern Southeast Asia.
- the rice field rat ( Rattus argentiventer ) is widespread in Southeast Asia.
- the Kinabalu rat ( Rattus baluensis ) lives on Mount Kinabalu in northern Borneo. Up to 20 cm tall, good climber, often on trees.
- the Aceh rat ( Rattus blangorum ) is only known from two specimens found in western Sumatra.
- the Nicobar island rat ( Rattus burrus ) is endemic to the Nicobar Islands.
- the Hoffmann rat or Minahassaratte ( Rattus hoffmanni ) lives on Sulawesi.
- Rattus koopmani is only known from one specimen that was found on Peleng, an island off Sulawesi.
- the small rice paddy rat ( Rattus losea ) occurs in Southeast China and Southeast Asia.
- the Mentawai rat ( Rattus lugens ) inhabits the Mentawai Islands off the coast of Sumatra.
- the black Mindoro mountain rat ( Rattus mindorensis ) lives in mountainous regions on the Philippine island of Mindoro.
- the Lompobatang Sulawesi rat ( Rattus mollicomulus ) inhabits a small area in southern Sulawesi.
- the osgood rat ( Rattus osgoodi ) is endemic to a small area in southern Vietnam.
- the Nicobar palm rat ( Rattus palmarum ) occurs only on the Nicobar Islands.
- the Sahyadris wood rat ( Rattus satarae ) lives in the Western Ghats in India.
- the Simalur rat ( Rattus simalurensis ) inhabits the Simalur island off Sumatra.
- the Andaman rat ( Rattus stoicus ) is endemic to the Andaman Islands.
- the Asian house rat ( Rattus tanezumi ) is widespread in East and Southeast Asia.
- the Tawi-Tawi wood rat ( Rattus tawitawiensis ) lives on the island of Tawi-Tawi, which is part of the Sulu archipelago.
- the Malay field rat ( Rattus tiomanicus ) occurs on the Malay Peninsula and in western Indonesia.
fuscipes group - native to Australia
- the Australian dark rat ( Rattus colletti ) lives in the north of the Northern Territory.
- the Australian bush rat ( Rattus fuscipes ) lives on the south and east coast of Australia.
- the Australian swamp rat ( Rattus lutreolus ) occurs in eastern Australia and Tasmania.
- the dark field rat or Australian pipe field rat ( Rattus sordidus ) is native to Queensland and southern New Guinea.
- the pale field rat or pale Australian field rat ( Rattus tunneyi ) has a fragmentary range in western, northern and eastern Australia.
- the Australian longhair rat ( Rattus villosissimus ) lives in central and northern Australia.
leucopus group - living on New Guinea and neighboring islands
- the Vogelkop mountain rat ( Rattus arfakiensis ) lives in western New Guinea. Their species status is unclear.
- the western New Guinea mountain rat ( Rattus arrogans ) inhabits mountainous lands in western and central New Guinea.
- the Manus rat ( Rattus detentus ) is endemic to Manus
- the Sula archipelago rat ( Rattus elaphinus ) lives on several of the Sula Islands that belong to the Moluccas.
- the Seram spiny rat ( Rattus feliceus ) occurs on the Moluccan island of Seram.
- The Giluwe mountain rat ( Rattus giluwensis ) is only known from one area in eastern New Guinea, but may be more widespread.
- the Japen rat ( Rattus jobiensis ) lives on several islands off the northwest coast of New Guinea.
- the Cape York rat ( Rattus leucopus ) occurs in large parts of New Guinea and on the northern tip of Queensland.
- the eastern New Guinea rat ( Rattus mordax ) is native to eastern New Guinea.
- the Papua New Guinea rat ( Rattus niobe ) lives in eastern New Guinea.
- the common New Guinea rat ( Rattus novaeguineae ) inhabits the central regions of New Guinea.
- the Arianus rat ( Rattus omichlodes ) is known from a small area in western New Guinea.
- the pocock highland rat ( Rattus pococki ) lives in the middle mountainous region of New Guinea.
- the great New Guinea spiny rat ( Rattus praetor ) is native to large parts of New Guinea, the Bismarck Archipelago and possibly also to the Solomon Islands.
- the Richardson New Guinea rat ( Rattus richardsoni ) is known from several places in the New Guinea mountainous region.
- the stone barbed rat or Mount Kunupi rat ( Rattus steini ) inhabits large parts of New Guinea.
- the Van Deusen New Guinea rat ( Rattus vandeuseni ) lives in mountainous regions in southeast New Guinea.
- the slender New Guinea rat ( Rattus verecundus ) occurs in large parts of the New Guinean mountainous region.
leucopus group - living on Sulawesi and neighboring islands
- the southwestern yellowtail rat ( Rattus bontanus ) lives in southwestern Sulawesi.
- the monkey tail rat ( Rattus marmosurus ) occurs in the middle and the northern Sulawesis peninsula.
- the Peleng yellow tailed rat ( Rattus pelurus ) is endemic to the Peleng Islands off the east coast of Sulawesi.
- the southeastern yellow tail rat ( Rattus salocco ) inhabits the southeastern Sulawesis peninsula.
- the north-eastern yellowtail rat ( Rattus xanthurus ) lives on the northern Sulawesis peninsula.
- not assigned to any group
- the annandale rat or Malay sunda rat ( Rattus annandalei ) lives on the Malay Peninsula and Sumatra.
- the enggano rat ( Rattus enganus ) is endemic to the island of Enggano off the south coast of Sumatra.
- the Philippine wood rat ( Rattus everetti ) occurs almost all over the Philippines.
- the Hainald rat ( Rattus hainaldi ) inhabits the Indonesian island of Flores.
- the Hoogerwerf Sumatra rat ( Rattus hoogerwerfi ) lives in northern Sumatra.
- the Sumatran mountain rat ( Rattus korinchi ) is only known from mountainous countries in northern Sumatra.
- the Maclear rat ( Rattus macleari ) lived on Christmas Island. This species is extinct.
- the Sri Lankan mountain rat ( Rattus montanus ) is endemic to Sri Lanka.
- the Moluccan prehensile tail rat ( Rattus morotaiensis ) occurs on the Moluccan island of Halmahera.
- the Christmas Island rat ( Rattus nativitatis ) was endemic to Christmas Island. This species is extinct.
- the Kerala field rat ( Rattus ranjiniae ) lives in southern India.
- the New Ireland wood rat ( Rattus sanila ) is known only from subfossil remains from the island of New Ireland (Papua New Guinea). It is unclear whether the species still exists.
- the Timor rat ( Rattus timorensis ) is known only by a 1,990 trapped on the island of Timor animal.
There are at least nine previously undescribed species that live in Thailand, the Moluccas and central Australia, among others.
It is not yet exactly clear whether the genus of rats is monophyletic , i.e. includes all descendants of a common ancestor. Wilson & Reeder (2005) think it is conceivable that at least some of the species that are not assigned to any group can be transferred to other genera.
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- For example Lars Walløe in his article “Var middelalderens pester og modern pest samme sykdom?” In: Historisk Tidskrift (Trondheim). 2010 vol. 89 issue 1 pp. 14-28 and M. Drancourt u. a .: " Yersinia pestis as a telluric, human ectoparasite-born organism". In: The Lancet Infectious Diseases . 2006, Vol. 6, pp. 234-241.
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