Introduced Rodents

 

The Black Rat, Rattus rattus

Introduction
The introduced Black Rat probably entered Australia accidentally when the First Fleet unloaded cargo in Sydney Cove. It has since spread throughout Australia, particularly in the south of the continent.

Black Rat, Rattus rattus

A Black Rat
Photographer/Source: Peter Robertson

Habitat
In Victoria, the Black Rat is known from agricultural and urban areas as well as bushland, where it is often mistaken for a native species. It is a good climber and is often found in the rooves of houses.

Identification
The Black Rat is easily recognised by its slender body and long tail (average length 230 mm), which is much longer than the length of the head and body (total average length 190 mm), and by its large, thin ears. The sleek coat on the rat’s back may vary from black to light brown. The underbelly is usually pale grey-white. Like other species of rodents, the Black Rat has orange-yellow incisor teeth with persistent pulps.

Diseases
In medieval Europe, the Black Rat was the main carrier of the plague bacillus, and even now its urine and faeces may carry the Salmonella bacillus.

The Brown Rat, Rattus norvegicus

Introduction
The Brown Rat also arrived in Australia with the early fleets, but it is still mainly restricted to coastal cities and ports.

Brown Rat, Rattus norvegicus

A Brown Rat
Source: Museum Victoria

Habitat
In southern areas the Brown Rat is sometimes found around farm buildings and along creek banks, but unlike the Black Rat it is not a climber and is more likely to be found in cellars, sewers around ports. If undisturbed, colonies survive in burrows.

Identification
The Brown Rat is a thickset, aggressive rat with a coarse brown coat, short ears and thick tail. Both the ears and the tail are often damaged and scabby. The tail in this species is shorter than the combined head and body length. Brown Rats take whatever human food is available, which can result in economic loss. Domestic strains of this rat are useful as laboratory animals and colour mutants are popular as pets.

The House Mouse, Mus musculus

Introduction
The House Mouse is the most successful of the introduced rodents and is found throughout Australia. Apart from its nuisance value in urban areas, it is an economic problem in the grain industry. Plagues of mice erupt in the grain-belt approximately once every four years and the results of their intrusion into grain areas are devastating.

House Mouse, Mus musculus

A House Mouse
Source: Ian McCann

Habitat
House Mice are also abundant in areas of natural vegetation, often about 18 months after a fire when populations of native mammals are at low density. House Mouse numbers then decrease as native species regain numbers.

Identification
House Mice are occasionally mistaken for small native rodents, even rare species. One sure method of identification is to examine the incisor teeth. House Mice have a prominent horizontal ridge on the rear of each incisor, which is not present in native species.

How do you tell the difference between a native and an introduced rat?

Native rats are often mistaken for introduced rats. In eastern Australia, people most often confuse the Bush Rat and the introduced Black Rat, Rattus rattus.


A Bush Rat
Photographer/Source: David Paul

This is an easy mistake to make. The two species are similar in size and both have fur that is quite variable in its colour and pattern.

The subspecies of Bush Rat that lives in eastern Australia is called Rattus fuscipes assimilis. Any Latin scholar will tell you that the latter name, assimilis, means ‘similar’. It was given the name assimilis because it looks so much like the introduced Black Rat.

Despite their similarities, there are a number of ways to distinguish between the Bush Rat and the Black Rat.

  • Bush Rats are shy. They rarely enter buildings and are usually found well away from human habitation. They do not construct nests in buildings. Black Rats, on the other hand, love to nest in buildings, particularly in rooves.
  • Bush Rats have rounded ears.  Black Rats have thin pointed ears.
  • Black Rats have long tails – their tails are as long, or longer, than the length of their bodies (from the snout to base of the tail). The tails of Bush Rats are shorter than their body length.


These are good identification points but it is always worth checking with a reliable expert.

Museum Victoria has a free identification service. If you would like to have something identified, you can attach a photograph to our online enquiry form or contact the Discovery Centre at the Melbourne Museum.

Further Reading

Menkhorst, P. and Knight, F. (2004). A field guide to the mammals of Australia. 2nd Ed. Melbourne: Oxford University Press.

Menkhorst, P. (Ed.) (1995). Mammals of Victoria. Oxford University Press. Melbourne

Strahan, R. (Ed.) (1995). The Mammals of Australia. Reed. Chatswood. N.S.W.

Comments (7)

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Dr.Kari 18 February, 2014 15:57
Please more info.
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Joseph Finn 9 August, 2009 10:56
Are you sure that your photo of a "Bush Rat" isn't a swamp rat? Bush rats seem to have longer heads and bigger ears. The picture you have there is easily distinguishable from a black rat.
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Discovery Centre 23 May, 2014 16:06

Hi Ben – as stated below, we don’t routinely respond to all published  comments as queries on our web pages, so Joseph’s comment above was taken as a comment rather than a query. The image in question has since been assessed by our current Curator of Mammalogy, an expert in rodents, and he’s indicated that the original animal was indeterminate from the image –we are sure that it wasn’t a Swamp Rat, as Joseph suggested, and we are confident that it also was neither a Broad-toothed nor Bush Rat as well.

In any case, it was perhaps not the most useful image for the purpose of this web page, so a new image, verified with certainty as a Bush Rat, has been uploaded as a replacement that should remove any doubt – thanks for bringing this to our attention

Ben 6 May, 2014 20:43
That bush rat looks even more like a broad-toothed rat. 5 years on and no reply to the previous comments?
Joseph Finn 9 August, 2009 10:44
The plague wasn't caused by Bacillus. It was Yersinia pestis and it came from the rat flea rather than the rat, and the flea easily infested humans because conditions were so filthy. Rats can carry all sorts of bacteria on their teeth like we all can, but Bacillus is not one of them.
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DARR DARR DARR 28 June, 2009 19:23
they aren't mice...they're rats.....well except for the house mouse hehe
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I HATE MICE 7 April, 2009 14:01
I HATE MICE
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