Rats and mice

Overview

Rats and mice are almost always present throughout suburban areas due to adequate food, water and shelter opportunities created by humans. Unfortunately they can never be eliminated but they can be controlled and all residents have a duty under the Health Local Law 2003 to ensure their properties are maintained to prevent rodent breeding. Rats can do considerable damage to buildings due to their need to gnaw on objects to keep their teeth short.

Signs of rodent infestation

Look for:

  • Droppings which are oblong in shape and about 12-20mm in length.
  • Remains of snail shells with the sides eaten out, nutshells, bones, seeds, etc. in the shed and other dark spots around the house.
  • Greasy marks along surfaces from rodent fur.
  • Fruit, vegetables and berries in the garden being eaten.
  • Burrow holes around buildings.
  • Damage to wood, soft metals, soap, food containers, conduit and cables from rodents gnawing on them.
  • Squeaking, gnawing or movement sounds in walls, cupboards, ceilings and under floorboards.
  • Pets being more excitable than usual.
  • Footprints and tail marks on the ground or along dusty surfaces.
  • Nests hidden in buildings made from rags, paper, cardboard, straw and other materials.

Preventing rat and mice problems

The presence and number of rats is determined by the availability of food and shelter. By denying the rodents these, you can effectively control rat populations. You can do this by:

  • Removing fruits and nuts from trees when in bloom and collecting rotten fruit from the ground.
  • Trimming palm tree branches and remove their fruits.
  • Keeping the backyard as clean as possible and free of debris and regularly removing garden waste and rubbish from sheds and around the yard.
  • Store wood off the ground and away from sides of sheds and fences.
  • Maintaining rubbish and compost bins in a good condition with secure lids and free from holes.
  • Keeping pet dishes clean and storing bulk pet food in sealed containers.
  • Cutting back trees away from the house to prevent easy access to the roof.
  • Blocking access holes into the house.
  • Ensuring disused containers are upturned so they do not collect rainwater.

Baiting

The most effective way of eliminating rodents is to bait them using poisons. Many brands are available at supermarkets and hardware stores but look for rat bait with coumatetralyl, bromodiolone or brodifacoum as the active ingredient. To avoid access to pets and children, you can wire wax blocks to trees and higher areas or you can also purchase rodent bait boxes which seal the baits inside. Place baits along rodent paths, in the roof, shed and dark spots around the house such as behind the refrigerator. Ensure you place baits in visible areas so they can be easily checked regularly to see whether they have been eaten. Replace the baits regularly and maintain supply for at least two weeks after you notice no more has been eaten. Rodents can develop a tolerance to the active ingredient so you may wish to change the type you use if you find they are not working.

Remember to always keep baits out of reach of children. If ingested, contact the Poisons Information Centre on 13 11 26 (open 24 hours). Vitamin K can be used as an antidote.

Trapping

An alternative to baiting is the traditional method of trapping using two types of traps - the old-fashioned snap back trap and a plastic capture box. Different types of bait can be used including bacon rind, chocolate, fish, nuts, prunes, apples or peanut butter. Rats can be suspicious of new objects or surroundings so they may stay clear of the trap until it becomes familiar. Placing the trap in the path of a rat and hiding the trigger under straw or cardboard is one way to get around this trap shyness. Traps should never be set above food or food preparation surfaces to avoid contamination by urine, droppings or blood. 

 

Rat facts

A rat can:

  • Fall 15 metres without hurting itself.
  • Swim 800m.
  • Tread water for three days.
  • Jump one metre vertically and 1.2 metres horizontally.
  • Wriggle through a hole one-quarter its own size.
  • Gnaw through lead and aluminium sheeting.
  • Produce up to 15,000 descendants in a year.

 

Further information you can refer to the Department of Health brochure Facts on Rats.  Around the world, rats and mice are known to spread over 35 diseases that can infect both people and pets, including: plague, salmonellosis, lepospirosis and tularemia. These diseases can be passed on by: direct contact such as rat bites, unsafe handling and disposal of infected dead rats, eating food or drinking water contaminated with rat urine, faeces, saliva, hair, or by breathing dust contaminated with the urine and faeces of infected rats. Diseases can also be transferred indirectly by ticks, fleas, and mites that live on infected rats.

Through their natural behaviours, rats can weaken building structures by: gnawing through lead and aluminium sheeting and chewing through electrical wiring, which can start fires by shorting-out appliances or lighting fixtures.

Major rodent pest species

Norway rat (Rattus norvegicus)

The Norway rat, also known as the common rat, sewer rat or brown rat, is the larger of the two pest rats. Females can have five-six litters per year, and average eight-10 pups per litter. The gestation period is 21 days and the young reach sexual maturity at three-four months. Norway rats are usually active at night. They are good swimmers and diggers and can communicate through high pitched vocalisation. The Norway rat is an omnivore, and will eat both plants and animal matter. They will eat almost anything, although they prefer starch and protein-rich food, such as cereals, which form a substantial part of their diet. Other foods they eat include meat, fish, vegetables, weeds, earthworms, crustaceans, nuts and fruit. The Norway rat is characterised physically by their:

  • brown or grey fur, and grey belly fur and grey feet
  • large build
  • blunt nose
  • short thick ears with fine hair
  • head and body length of 20–27 cm
  • tail length of 16–20 cm
  • weight of 200–500 grams
  • banana or sausage-shaped droppings.

Roof rat (Rattus rattus)

The roof rat, also known as the ship rat or black rat, is smaller than the common Norway rat. Their life span is usually nine-12 months. Females can have four-five litters per year, and average six-eight pups per litter. Sexual maturity is reached at three-four months and females have a gestation period of 21 days. Roof rats are usually found in built-up areas or near the coast. They have good climbing ability and can nest in buildings, roof voids and ships. Roof rats eat a wide variety of food items, and generally feed on cereals, grains, fruit, and almost any item that has nutritional value. They are omnivores and will feed on insects or meat if necessary. The roof rat is characterised physically by their:

  • grey, black or brown fur, with occasional white belly fur
  • head and body length of 14-20 cm
  • tail length of 25 cm
  • small, slender, streamlined build
  • weight of 200-300 grams
  • pointed nose
  • large, thin, almost hairless, translucent ears
  • pink feet
  • spindle-shaped droppings.

House mouse (Mus domesticus)

The house mouse is small. They have a life span of approximately 12 months. Females can have six-10 litters per year. Sexual maturity is reached at about six weeks, with a gestational period of three weeks. House mice are curious animals and can live indoors or outdoors in close proximity to humans. They have a wide and varied diet including fruits, nuts, grains, animal feed and cereals. The house mouse is characterised physically by their:

  • brown or grey fur
  • head and body length of eight-10 cm
  • tail length of eight-10 cm
  • weight of 14-20 grams
  • small slender build
  • pointed nose
  • large, hairy ears
  • pink feet
  • small spindle or irregular-shaped droppings.

To report a problem

To report a neighbourhood noise issue, please call Customer Service on 9311 8111 or email admin@vicpark.wa.gov.au with your contact details and address of the property of concern. Your request will be allocated to an Environmental Health Officer for follow-up.

If you report this after hours you will be transferred to the out-of-hours service where you can leave a message. If there is a Ranger available they will attend, however they are not authorised noise officers so take action but can collect evidence. Your complaint will be received by an Environmental Health Officer the next working day.