Rats and Mice

What are Rats and Mice and how to get rid of them

Rats and mice are prolific breeders and if left uncontrolled can quickly develop into plague proportions. High reproductive rate, the ability to survive on a wide range of food sources and ease of travel throughout their environment, contributes to their astounding success.

Rats and mice can carry parasites, such as fleas and ticks, and diseases such as plagues, leptospirosis and typhus fever, some of which can be transmitted to humans, pets and livestock. Transmission is often caused by rat and mouse scratches and bites, or by coming into contact with their saliva, faeces and urine. Contamination and wastage of human food, pet food and bird seed is attributed to the parasites, diseases and other germs brought in by rats and mice.

Rats and mice can cause serious damage to possessions and property from gnawing on building materials, structures and wiring; producing stains, foul-smelling odours and mess; and feeding on crops, garden plants and gardening products.

Given the serious risks and extensive damage, it’s important to prevent, control and monitor for rats and mice in and around the house and garden.

Description

Rats and mice are small rodent mammals which are distinguished by perpetually growing chisel-like front teeth. One pair lies in the upper jaw, while the other pair is in the lower jaw. The Black Rat, Brown Rat and House Mouse all have yellowing enamel on their front teeth and generally live in small to large groups.

• Black Rat, Ship Rat, Blue Rat, Bush Rat or Roof Rat (Rattus rattus) is a medium sized rat. Body is slender and 350 mm to 460 mm in length, nose to tail. The coat is silky smooth and is light brown or charcoal grey on the back, with a slightly lighter coloured belly. The head is long with a rounded face, pointed nose and long whiskers. Eyes are large. Ears are prominent, large, thin and hairless. Tail is similar colour to the upper coat, hairless, scaly and longer than the rest of the body (185mm to 255 mm). Although it is most active at night, it can be seen during the day and is unafraid of humans. An accomplished climber, it disfavours water and swimming, and prefers to stay near to the nest when finding food.
• Brown Rat, Norway Rat, Sewer Rat or Water Rat (Rattus norvegicus) is a large sized rat. Body is stocky and 330 mm to 470 mm in length, nose to tail. The coat is coarse and is grey-brown, sometimes black, on the back and sides, with a white to grey belly. The head is long with a stunted nose and mouth (muzzle), a straight face and long whiskers. Eyes are small. Ears are close together, set into the head, small and hairless. The tail is scaly, hairless and shorter than the rest of the body (150 mm to 215 mm). It is mostly active in the early evening and at night.  They are excellent swimmers and travel long distances from the nest to find food.
• House Mouse (Mus musculus) body is rounded and 135 mm to 200 mm in length, nose to tail. The coat is soft and is light-brown to black on the back with a white to light yellowish-brown belly. The nose is pointed with long whiskers. Eyes are black, large, prominent and bulging. Ears are large, rounded and generally naked. The tail is slender, generally hairless with circular rows of scales and is approximately the same length as the rest of the body (75 mm to 100 mm). Although they are good climbers, jumpers and swimmers, they prefer to stay close to their nest area.

Lifecycle

• Black Rat (Rattus rattus) lives for about 2 years. After mating, females gestate for 22 days and give birth to a litter of 5 to 12 live young. Young are fed on milk for up to 28 days and reach sexual maturity within 4 months. Females may have up to 6 litters per year and produce a subsequent litter within 27 days of their previous litter.
• Brown Rat (Rattus norvegicus) lives for about 2 years. After mating, females gestate for up to 24 days and give birth to a litter of 6 to 14 live young. Females can lay up to 7 litters per year. Young are fed on milk for up to 28 days and reach sexual maturity within 4 months.
• House Mouse (Mus musculus) lives for about 1.5 years. After mating, females gestate for up to 21 days and give birth to a litter of 3 to 12 live young. Females can lay up to 14 litters per year. Young are fed on milk for up to 23 days and reach sexual maturity within 5 to 7 weeks.

Habitat

Rats and mice prefer warm, dry, sheltered and quiet areas with access to food and water. They are generally most active during the night, although they may also be seen during the day.

Rats and mice can be found in the home and garden at anytime of year, however they are especially known for entering indoor areas in autumn and winter to escape the cold.

Rats and mice can be found in:

• Urban areas, farmlands and natural areas such as bushlands and coastal regions.
• Rooms: in any room in the house, especially kitchen, bathroom, laundry, garage and shed.
• Other areas inside the house: in any area of the house such as the roof, ceiling, in the wall cavity, under the floor and under the house.
• Under or inside any item in the house such as machinery, appliances, furniture, boxes, bathtubs, cupboards, pianos and drum kits.
• Outdoors: in the rubbish and compost bin; in debris such as piles of wood and rubbish; in trees; in dense vegetation such as long grass and thick shrubs; in sewers and pipes; and in animal houses such as chicken coops and kennels.

Rats and mice are omnivores and feed on a wide variety of animal and plant material such as:

• Human food: including cooked and uncooked foods; decomposing food; food spills and crumbs; food waste.
• Pet food and bird seed.
• Crops such as roots, tubers, fruits, vegetables, nuts, and grains.
• Eggs in chicken coops and bird nests.
• Snails, insects, spiders and small animals such as skinks, fish, tadpoles, frogs, young birds and rabbits.
• Organic waste in compost and rubbish bins.
• Organic fertilisers such as blood-and-bone.
• Fresh meat and carrion (long dead animals.)

Natural enemies

Birds, reptiles, other rats and mice, dogs, cats, foxes, parasites and diseases.

Symptoms of Rats and Mice damage

The obvious sign of an infestation is a living or a dead mouse or rat. Other ways to further identify rats or mice in and around the house and garden include:

Droppings

• Droppings are the most significant indication of a rat or mouse.
• Droppings, or faeces, are normally dark brown to black and made into small piles.
• The shape is long, thin and rounded and may be rice shaped or slightly curved.
• Mice droppings are usually 2 mm to 6 mm long, while rat droppings are generally 9 mm to 19 mm long.
• Fresh droppings are soft and glisten due to high moisture content. Older droppings are dry, hard and dull in appearance.
• Droppings can be found inside cupboards, on benchtops, near the edges of the room, under appliances, in the oven and in most other areas rats and mice are known to inhabit (see ‘Habitat’ above).
• Droppings are not found near nesting areas.

Urine stains

• Rats and mice urinate as chemical communication to mark territories, attract mates, identify one another and their status, and for spatial awareness.
• Rats and mice urinate on each other, food, objects, walls, floors and on other surfaces.
• If infestations are left unattended, urine spots can develop into urine pillars made up of constant urination and a mixture of dust, hair and other fine-particle debris.   

Hairs

• Hairs are lost through grooming which are covered in saliva.
• Hairs are also shed during moulting season a few times a year, resulting in thousands of lost hairs.

Nests

• Nests are often made from shredded paper, insulation, leaves, rubbish and other debris.
• Generally found inside the roof, under the floor, in the shed, garage, chicken coop or garden.
• Brown Rats prefer to live in burrows in the ground. Often seen on the outside of buildings and other structures; as well as underneath piles of wood and other debris. Entry holes are approximately 75 mm in diameter and may have piles of earth at the entrance.
• Indoors, Black Rats prefer to live in the roof, ceiling, walls and in other protected areas, while outdoors they live in trees and dense vegetation.

Odour

• Odours are mostly produced from urine and faeces.
• May also be a musky animal odour.
• The foetid odour produced from the decomposition of a dead rodent will last for about 2 weeks.
• Odours may be present lingering in the air in any room, or may be more concentrated inside cupboards and other enclosed spaces.

Gnawing

• Rats/mice have perpetually growing teeth so they wear down their teeth by gnawing on hard objects and surfaces such as timber, wiring and pipes.
• Items which may be damaged by gnawing include furniture, cupboards, posts, window and door frames and building materials.
• Chewing of food packaging, often along the sides and in corners of plastic bags and cardboard boxes filled with food.
• Chewing to get into an area such as into cardboard boxes or through plasterboard walls.
• Gnawing and feeding damages trees, shrubs and crops such as fruits and vegetables.

Tracks, foot prints and tail marks

• Rats and mice are creatures of habit and tend to walk along the same routes.
• Paw prints and wavy lines that are sometimes made by dragging the tail are found in dusty areas, or made after getting into foodstuffs such as flour.
• Indoors, paw prints, tail marks and tracks are often found along walls, behind furniture and other objects.
• In outdoor areas, well-defined runway tracks are formed in dense vegetation such as long grasses and in thick groundcovers.
• Rats and mice have four toes on their front paws and five toes on their back paws. The front paws are smaller than the hind pair. The length of the hind pair paws, from heel to longest toe) in adult mice are about 10-20 mm, whereas rats are about 25 - 40 mm.

Burrowing

• Burrows can be made in the ground, sometimes developing into extensive tunnel systems.
• Rats and mice can dig under structures, walls, fences, compost bins and plants.
• Depending on the substrate, rats can dig as deep as 1.8 metres.

Rub marks

• Rub marks are yellowy, sometimes dark smears, often mixed with hairs.
• The marks are primarily caused by the secretion of a yellow and greasy substance called lanolin produced from their oil glands. Lanolin, along with their ability to dislocate the rest of their body, allows rats/mice to squeeze through small holes. Lanolin mixed with dirt causes the rub marks to appear as brown oily smears.
• Can be seen on furniture, upright roof timbers, skirting boards, on walls, around holes in the walls and other entry-points.

Sounds

• Sounds are generally heard at night:  squeaking, scurrying, scratching, climbing, burrowing and creating nests.
• Mostly heard in in the roof, under floor and in wall cavities.
• Rats and mice have perpetually growing teeth and to help wear the teeth down, can be heard grinding timber and pipes.
• Possums may also make noises in the roof, however sounds made are distinguished by much louder thuds which are not heard again during the day.
• Sounds made by birds nesting in the roof and gutters are often accompanied by chirping.

Behaviour

• Hoarding or movement of food back to the nest or less exposed feeding sites. At feeding sites there may also be an accumulation of food packaging, bones, seed husks and other debris. Feeding sites may be found in walls, ceilings, roofs, dense vegetation, and under the house, in piles of wood and other debris.
• Rats are generally cautious of new things in their environment, while mice are generally more curious.
• If threatened, rats may bite. It is safest never to approach a living or dying rat/mouse.
• Rats and mice are agile climbers and can climb vertical walls, wiring, pipes and other structures; and are also great jumpers and swimmers.
• Rats and mice have poor vision but excellent smell, hearing and taste.
• Unlike feral rats and mice, native rats and mice are very shy and rarely seen in urban areas.

Signs of rats and mice are sometimes confused with birds, possums, and other animals. Before setting out any baits, traps or repellents, ensure the issue has been properly identified from various signs of rats and mice.

How to prevent Rats and Mice appearing

Monitor regularly, checking for signs of rats and mice (see ‘Symptoms of Rats and Mice damage’). Preventing rats and mice will not only reduce the likelihood of future infestations, but will also help to control a current infestation.

Remove entry points:

• Repair holes, cracks and gaps in walls, skirting boards, window frames and door frames.
• Seal any breaks or openings in the house with wire mesh or copper wool.
• Cover any open pipes or drains with grates.
• Ensure garage doors seal properly.
• Repair doors and windows so they close properly.
• Ensure flyscreens are fitted and maintained
• Keep windows and doors closed, unless properly fitted with a flyscreen or screen.
• If possible, cover vents with a fine wire mesh.
• For aviaries, bird cages and chicken coops, try installing heavy grade flyscreen or fine wire mesh.

Remove shelter sources:

• Remove weeds.
• Prune dense vegetation such as long grasses and dense shrubs.
• Regularly mow the lawn.
• Keep house, shed and garden free of clutter.
• Remove any materials that can be used for nesting, such as roof insulation, fabric and paper materials.
• Remove any building materials, piles of wood or debris on the ground.

Remove food sources:

• Keep all food in plastic sealed containers or in the fridge.
• After using the kitchen wipe, down benches and pick up any dropped food and crumbs.
• Clean food appliances well after use, such as the toaster or sandwich press.
• Regularly clean underneath appliances, such as the fridge, oven and dishwasher.
• Clean any spilt food on the outside of containers, such as sauce bottles and jars.
• Store toothbrushes in sealed containers.
• Keep night-time drinking water in sealed bottles.
• Ensure rubbish bins are well-maintained, free of holes and lids are firmly secured.
• Dispose of rubbish regularly, especially before going to bed of a night or leaving the house during the day.
• Rinse food waste residues out of recyclable packaging.
• Thoroughly clean outdoor barbeques after use. Keep collected oil and grease in drip pans/trays in a plastic sealed container until ready for disposal. Ensure any dropped food is collected and disposed of.
• For crops, such as capsicums and tomatoes, try securing bird netting firmly around garden beds. 
• For fruit trees, ensure all fruit which has fallen from the tree is picked up promptly; plant fruit trees in a position where rats and mice cannot hop from one tree to the other; try crown-lifting low-hanging fruit bearing branches; and install a slippery tree guard along the trunk of the tree to stop rats and mice from climbing up.
• Store organic fertilisers, such as Blood and Bone, in plastic sealed containers.
• Ensure compost bins are maintained properly and located away from the house. Otherwise, discontinue use of compost bin until rats and mice have been properly controlled. Alternatively, use in-ground composting methods.
• Unless necessary, avoid leaving pet food and bird seed out for extended periods of time.
• Ensure bird nests have been removed from inside the roof, in the shed and garage, and in other areas such as gutters. For native birds, contact your local wildlife rescue for advice.

Remove water sources:

• Repair leaky taps and pipes.
• Eliminate where practical any standing water such as bird baths.
• Wipe up water on benches, in sinks and on the floor, especially before going to bed at night or leaving the house during the day.
• Ensure rain water tank openings are fitted with a firmly secured mesh. See tank manufacturer for further advice.
• Keep the lid of the toilet closed, especially on outdoor toilets.