Rats & Mice Facts

Rats and mice are mammals of the Order Rodentia (rodents). There are three rodent pests of houses in Australia - all introduced species. They are the Norway rat, the roof rat, and the house mouse. Rats and mice require food and shelter like most animals

Rats and mice are mammals of the Order Rodentia (rodents).  There are three rodent pests of houses in Australia - all introduced species.  They are the Norway rat, the roof rat, and the house mouse.

Rats and mice require food and shelter like most animals, and these are provided in buildings, particularly during late autumn and winter, when they enter houses.  These conditions also complement their breeding.  Once inside buildings, they often make their nests in walls and roof cavities.  The nests are usually composed of paper and other soft materials such as insulation batts.  In the case of the rats, particularly the Norway rat, burrows are made in soil - often near buildings and garbage disposal areas.  Rats and mice are also very good climbers, being able to ascend rough walls, pipes, trees and vines and walk across cables from one structure to another.

Rats and mice are mostly active at night.  They eat a wide range of foods.  The senses of rodents - such as smell, taste, hearing and touch - are very keen, but their sight is poor and as a result they tend to remain close to various surfaces.  They are sensitive to all environments and move around the edges of rooms rather than across them.  Rodents, especially rats, have a fear of new objects (neophobie) in their search for food and usually use their same tracks.  This is important when baiting and trapping for it may be some days before they investigate a bait station or trap.  Mice are likely to investigate more quickly any changes in their environment compared to the two species of rats. 

Grooming by licking their fur and feet is a normal practice for rodents.  The action of the tracking powders containing anticoagulants is dependent on this.

Norway Rat (Rattus Norvegicus)Norway Rat (Rattus Norvegicus)

This is the largest of the three, and is a major pest in the most human environments where food and shelter are available.  It is often present in food handling facilities, sewers, garbage areas and on most types of farms.  Unlike mice and roof rats, Norway rats make burrows in the soil and have concealed escape holes known as ‘bolt holes’.  In cold weather, particularly in highland areas, they will live inside buildings, making their nests in walls and roof cavities.

The Norway rat weighs about 450 grams.  It has a blunt nose area, its tail is shorter than its body length, and its ears are close-set and small.  The fur is a coarse brown colour.  It lives about one year, and during that time, produces five to six litters - each having about eight young.  When other rodents are also present, the Norway rat is the physically dominant species.

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Roof Rat

Roof Rat (Rattus Rattus)

The roof rat is usually found in city and suburban areas where the human population density is higher than in the country.  They usually nest indoors but also outside where the vegetation gives them nesting security.  When in buildings, they nest in roof cavities.  They are good climbers and travel up and down pipes and across various forms of insulated wiring.  Roof rats prefer vegetables, fruit, and cereals.

The roof rat weighs about 250 grams, has a pointed nose and large ears that are almost hairless.  It is a uniform colour of grey, black or brown fur, and may be white underneath.  Its tail is longer than its entire body.  The life expectancy of the roof rat is about one year, during which time four or five litters are produced - each having six to eight young.

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House Mouse

House mouse (Mus Musculus)

The house mouse is also known as the ‘field mouse’.  When it is located outside, it is a yellow-brown colour, paler than those living inside, which are usually a darkish grey colour, with lighter grey on the belly.  As it is a small rodent, it has easy access to the home, and nests in walls, cupboards, and roof cavities.  It makes small burrows when outdoors.  It has a low water requirement and feeds on many foods such as grains, fruit and various animal and human foods.  Mainly nocturnal, it will also feed during the day, and will be attracted to new food rather quickly.  Contamination of food and kitchen utensils with their urine and faeces occurs whenever mice are present.  Mice can reach plague proportions on farms and properties in rural areas where they feed on stored products of grain and vegetables.

The house mouse weighs about 20 grams, and lives for about one year, during which time it generally has 6 - 10 litters, each having five or six young.  It has rather large, hairy ears and a pointed nose, and its tail is about the length of its body.

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Black Rat

The Black Rat, also known as the Asian black rat, ship rat, Roof Rat or House Rat is a common long-tailed rodent of the genus.

Despite its name it comes in several colour forms.  Compared to the Brown Rat, it is a poorer swimmer but more agile and a better climber, tending even to flee upwards.  It is usually black to brown in colour with a lighter underside.  A typical rat will be 15 to 20 cm long with a further 20 cm of tail.  It is nocturnal and omnivorous, with a preference for grains.  In a suitable environment it will breed throughout the year, with a female producing three to six litters of up to ten young.    Females may regulate their production of offspring during times when food is scarce, throwing as few as only one litter a year.  Rats live for about 2-3 years.

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Brown Rat

The brown rat, common rat, Norway Rat is one of the best known and common rats and also one of the largest.

The fur is coarse and usually brown or dark grey, the underparts are lighter grey or brown.  The lengthy can be up to 25 cm with the tail a further 25 cm.  Adult body weight averages 350g in males and about 250g in females but a very large individual can reach 500g.  Brown rats have acute hearing and are sensitive to ultrasound and also possess a very highly developed olfactory sense.  Their vision is poor, around 20/600 for normal rats,  They are dichromates who perceive colour rather like a human with red-green colour blindness and their colour saturation may be quite faint.

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Mouse 

A mouse is a rodent that belongs to one of numerous species of small mammals.  The best known species is the common house mouse.  It is found in nearly all countries ad as the laboratory mouse serves as an important model arganism in biology.

The average mould in the wild lives only about 5 months, primarily due to heavy predation.  Cats, wild dogs, foxes, birds of prey, snakes and even certain kinds of insects have know to prey heavily upon mice.  Nevertheless due to its remarkable adaptability to almost any environment and its ability to live commensally with humans, the mouse is regarded to be the third most successful mammalian species living on Earth today, after humans and the rat.

Mice are small rodents, resembling diminutive rats,  They usually have pointed snouts and small ears.  The body is typically elongated with slender, usually hairless tails, but different types of mice show large variations.

Mice will eat mead, the dead bodies of other mice and have been observed to self-cannibalise their tails during starvation.  Mice eat grains, fruits and seeds for a regular direct which is the main reason they damage crops.  Mice are also known to eat their own faeces.  Mice are often portrayed to enjoy cheese and people sometimes use it as mousetrap bait, though mice actually do not like cheese due to its fatty texture.  Instead, they like food that contains high sugar, although chocolate is a toxic to them.

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Detection

The presence of rodents is often detected from their damage, odour, and faecal droppings.   Droppings of about 18mm indicate the Norway rat, 12 mm the roof rat, and 3-4 mm the house mouse.  The following signs should always be investigated to confirm rat and mouse presence prior to trapping or baiting:

  1. Runways, showing up as greasy nooks on furniture and walls from the rodents’ fur
  2. Urine stains on surfaces of floors and cupboards
  3. Disappearance of food
  4. Sounds, often occurring at night, which may include squeaking and fighting
  5. Nests behind cupboards and lounges, made of paper and rags, and sometimes snail shells.

Pets are sensitive to other animal intruders and often bark when rodents enter houses or are active.  Once the rodent activity has been detected, it is then important to determine which rodent is present for this will determine the control.

Non-chemical control

The prevention or termination of rat and mouse infestations by sanitation and hygiene is the most satisfactory control procedure.  The use of vacuum cleaners to reduce food particles on floors is important but must be accompanied by using sealed food containers.  Tight-fitting lids on garbage bins is also important. 

Rodent-proofing of properties prevents most access to a building.  Holes in walls for water and drainage pipes should be sealed to prevent rodent access.  Usually cement or metal sheeting prevents access.  Inspection of the building to locate entry points is a first step in proofing.

Trapping rats and mice is often done by homeowners and pest-control technicians.  There are several types of traps - from the simple single snap trap to multiple mouse-catching devices that can hold up to 30 mice.  The single snap trap may be used with a bait or set unbaited.  Suitable foods for baited traps include bacon, nuts, and apple.  Unbaited traps have a trigger covered with fine pieces of cardboard or sawdust.  They are placed in one of the runways, usually at right angles to them. 
Because trapped rats and mice may exude blood, urine or faeces, traps should not be set near food preparation areas.  When a rodent is caught, its fleas leave the dead body and seek other hosts.  It is therefore important to check traps frequently and remove the dead rodent together with its fleas, at the same time.

Glue boards, which have an attractant in the glue, may be used in homes, but must be inspected regularly.  Once on the glue board, the rodent must then be killed - not always a desirable task.