Types of Rats

There are two species of rats known as “true rats”—the types recognized worldwide as pest animals: the Black Rat (rattus rattus) and the Brown Rat (rattus norvegicus). Both species are known by a variety of other names. The brown rat is also called the wharf rat, street rat, common rat, hood rat, Norway rat, Norwegian rat, sewer rat and Hanover rat. The black rat species has been referred to as a ship’s rat, roof rat, Alexandrine rat, house rat and Old English rat.

The Black Rat

By the first century of the current era the black rat had spread into all areas of Europe, including the British Isles (thanks once again to Roman invasion). From that time forward, black rats have spread to nearly ever spot on earth, alongside European explorers and settlers.The black rat is believed to have originated in the tropical areas of Asia and began to spread into the Middle East around the time of the Roman military expansion into the area. Black rats are famous for infesting ocean going ships, it is likely that Romans returning from the near East carried the first black rats in invade Europe in the holds of their ships.

The black rat actually varies in color from black to a light brown. The black rat’s underside is usually lighter in color than the rest of its body. In size the black rat is smaller than the larger brown rat. The average adult black rat is between 12.75 and 18.25 inches, which includes the tail which can take up between 6 ½ to 10 inches of its length. Weight varies between 4 to 12 ounces. Black rat fur is often described as scraggly.

Black rats are omnivores, but favor plant material such as grain, fruit and seeds, but has also been known to eat insects, feces and animal derived refuse. They are scavengers who survive by exploiting whatever plant or animal remains they encounter in their environment.

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Black rats a good swimmers, and excellent climbers, which helped earn them their alternate name as roof rats. While the brown rat prefers more terrestrial habitats, the black rat’s ability to climb finds them infesting attics and roofs, accessed via power and telephone lines connected to human dwellings. Their favored nesting space is roof rafters where they build their nests from grass and twigs.

Black rats can produce anywhere from three to five litters a year following a breeding season which extends in most areas of the world between March and November. Litters can be as small as one infant or as large as 16 rat pups; the average litter size is around seven babies.

Female rats are able to breed at 12 weeks of age, and can successfully breed and conceive at the same time as they are suckling their current litter. These two factors result in a single female being able to produce an enormous number of young. Black rat lifespans in the wild are just under 18 months, due to predation and pest control.

The black rat species has been historically considered the disease vector of the Bubonic plague—the bacterium Yersinia pestis inhabits the digestive systems of black rat fleas. Black rats with some kind of natural immunity to the disease itself (surviving to spread the infected fleas) are deemed responsible for the dreaded disease’s pandemic in the fourteenth century. However, many experts now believe that this was only one of several paths that Yersinia pestis took during the Black Death. Black rats do transmit several diseases to humans, and also pose significant threats to food stores and property.

The Brown Rat

The designation as “Norwegian” originated with a British naturalist John Berkenhout who hypothesized that the brown rat had invaded England via Norwegian ships in 1728. There were however, no known populations of brown rats in Norway at that time. The name has stuck in spite of the refutation of the animal’s origins.Despite one of their alternate names being the Norway rat, brown rats are believed to have originated in Northern China. They now can be found on every continent except Antarctica.

Brown rat fur varies from brown to a very dark grey and, like the black rat the underbellies tend to be lighter variants of the animal’s predominant color. Brown rat fur is coarse in texture and shot through with black hairs. Brown rats have a body length of around 10 inches, their tails are usually of the same length as their bodies. Weight runs from 550 grams (19 ounces) to as large as 900 grams (32 ounces).

Brown rats are ominvores and scavengers, but prefer cereal grains. A study of brown rats revealed that scrambled eggs were their favorite meal, followed by macaroni (and cheese!), and cooked corn. Brown rats were found to be least fond of vegetables and fruits. Different populations of brown rats tend to exploit different food sources, colonies near fish hatcheries will dine on fingerling fish; riverside populations have been known to dive for mollusks; North sea island dwelling rats have been observed stalking and killing sparrows and ducks.

Brown rats are known as excellent swimmers, but unlike the black rat, are poor climbers. Brown rats are prodigious diggers, they produce sprawling burrow systems. They favor burrowing next to existing structures which they can exploit for food and water sources; they use the burrow systems for food storage, shelter and nesting sites. Inside structures they tend to stick to established routes, running along the bases of walls. When threatened they prefer to withdraw to their burrows. When burrowing is not possible, they prefer damp subterranean nesting sites including cellars and sewers.

Click here to see pictures of Brown Rats
Brown rats breed year around and reach sexual maturity at five weeks of age. Litters vary in size numbering up to fourteen infants although like the black rat the average number of young is seven. Brown rat females can produce five litters a year. Brown rats can live as long as three years, but on average only survive a year in the wild due to pest control and predation.

Brown rats packs are socially stratified, each individual in a pack has a particular place and is dominant over another rat. Brown rats sleep together in packs and engage in mutual grooming. They huddle together for warmth and social interaction; they have been observed “nosing” that is adult rats nuzzling each another in the neck. They also play, wrestle and chase each other, and squabble over dominance.

Brown rats are not favored by the species of rat fleas that carry Yersinia pestis, and so is not a vector for bubonic plague. They do figure in the transmission of several other diseases than can affect humans, including toxoplasmosis which is often transmitted from the rat to a cat feeding upon it, and from there to a human via exposure to cat feces in litter boxes. Rat bite fever is transmitted by brown rats, as is Weil’s disease, viral hemorrhagic fever, Q fever and Hantavirus pulmonary syndrome.

Brown rats are the source species for Pet or Fancy rats; and laboratory rats. The latter are descended from albino brown rats and have been used in psychological, medical and other biologic experiments. Their rapid rate of reproduction and quick maturation rates make them easy to keep and breed they are considered an important model organism for better understanding human disease and behavior.

3 thoughts on “Types of Rats”

  1. Hi There

    We have been building down into our cellar and we now know our builder is a ‘cowboy’ – for many and various reasons.

    Last week the basement had a really bad smell in it. It was the smell of rotten meat / something dead. I know the smell because I have worked in the meat industry in the past.

    The builder has left many unfilled holes around the concrete floor where it meets the walls. We checked those holes at the time – could not detect the smell coming from any of them specifically but the smell was worse in the bedroom. There is a large hole in the corner of that room. After a day the smell went away which I thought was odd as I know the only way to remove such a smell is to locate and remove the source of it, which we had not done.

    There were no rat droppings or any evidence of rats at that time.

    This morning I went down to the unfinished basement – there are now stairs in place. I did not specifically check anything but I did enter the bathroom. Nothing seemed unusual to me.

    My daughter went down to the bathroom about an hour later (which is almost finished) to get something from the sink drawers. She called up and asked me what all the blood was. I went down and there was quite a lot of blood on the bathroom floor. We have a white concrete floor outside the bathroom, about to be sealed, and there were spots on that too. I followed those into the bedroom that smelt bad last week. There were rat droppings and blood in that room.

    I heard a noise from the hole in the corner and was able to see a rats nose twitching in there and general movement. The fur colour seems to be fairly light – not black.

    I have now sealed as many of the holes in that room including an area where it could get behind the bathroom wall, as the walls are not yet fully sealed. I left the ‘rathole’ open. I then sealed the room. I say sealed, only with plastic sheeting as it is all we have – its very thin and could easily be bitten through but it is Sunday, stores are closed, and it is all I have to hand.

    The only food source down there would be wooden walls as far as I know. But also maybe dead rats?? I’m wondering if the smell was a dead rat and maybe others ate it thus removing the source of the smell? Is that possible?

    So do you have any advice? Could they be under the concrete slab?

    I am aware of the various health risks as we live upstairs and have all been recently ill with flu-like symptoms including chest-pain when breathing which is not a common flu symptom.

    Going out of our minds with worry here today – any advice would be very gratefully received.

    I live in Oslo – Norway.

    Thanks in advance.


  2. I was out in my garden yesterday in the UK. And I had the unfortunate experience of spotting a brown rat in our garden… It went underneath the shed for ten mins then went to check out the bbq before I ran at it and then it went behind the compost bin then its gone. We’re recently moved into our house and are going to be tidying the garden. Removing the shed and sealed compost bin. We also live right next to a conservation river so my question is really can I ever stop this? Please let me know your opinion. I am pretty sure they aren’t in the house at all. Thank you

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