What does it look like?
Norway rats are the larger of the two European rats found in New Zealand. Their coats are grey-brown and shaggy with a pale underside. They are distinguished from the ship rat in that the tail, which is about 180 mm in length, is thick and shorter than the body, which is about 200 mm in length.
Ship rats are smaller than Norway rats, but their tails are larger, thicker and longer than their bodies.
Rats are mainly nocturnal. They have a varied diet that includes native birds, eggs, chicks, invertebrates, frogs, and lizards. They eat large quantities of native seeds, either from the ground or straight from the tree (as in the case of Ship rats, which can climb high into the canopy). Norway rats are common in wet habitats and urban areas. Ship rats are found in most habitats, and they are the most abundant and widespread rat on mainland New Zealand.
Why is it a problem?
Since their arrival in New Zealand, Norway and ship rats have had significant impacts on native flora and fauna. They have been implicated in the decline of many native species including the bellbird (korimako), robin (toutouwai), stitchbird (hihi), saddleback (tīeke), native thrush (piopio), parakeets (kakariki), flightless weevil and giant weta. Between these two species of rat and the kiore (Rattus exulans), which is only found on several offshore islands, there are no habitat types that go unexploited for food resources.
Rodents are prolific breeders. Rats can reproduce throughout the year if conditions are suitable, with a female producing up to five litters a year. They can live for three years but wild animals probably live for less than a year.
Control methods
Poison
Poisoning can be an effective method to control a rat infestation or to achieve control over a large area. Most rodent poisons are anticoagulants. Rats generally die within seven days.
It’s recommended poison baits are placed within purpose-built bait stations to protect bait from the weather and protect non-target animals (like pets and birds) from feeding on bait directly. Placing bait in bait stations will help prevent rats removing bait and storing it in other locations. Check bait stations regularly, if all the bait is gone within the first night of baiting, more bait stations are required. Remove any mouldy bait and replace with fresh bait. Wear gloves when refilling a bait station for your own protection and to minimise putting human scent onto the station and the bait within.
Always read the label before using poison. Make sure you follow instructions and understand the symptoms of accidental poisoning and how to treat it.
Put rat baits in secure places away from children, pets and stock.
In case of accidental human consumption, contact the:
National Poisons Centre on 0800 764 766 for advice.
Rat poison can be extremely harmful to dogs and cats. Symptoms can take several days to appear. They may include lack of appetite, lethargy, bleeding from the nose or mouth and pale gums). Vitamin K can be used as an antidote. Call your vet immediately if an animal accidentally eats rat bait.
Traps
Trapping is best suited to small rat infestations. It’s particularly good in buildings, where using poison and having rats die inside is not ideal. Trap covers can be made out of coreflute (the material that real estate signs are made of). These keep the lure dry and prevent other animals being caught. These should be blocked at one end and tall enough that your traps can operate properly. Traps need to be checked and lured regularly: peanut butter works well.
Traps used to kill rats include modified Victor Pro trap with tunnel, Victor Pro trap with tunnel, BT200, DOC200, BT250, DOC250, Monster trap, Goodnature A24 rat and stoat trap.
More information about these traps can be found at the Trapping link below.
Prevention
The presence of rodents can be a sign that a clean-up of the house, shed, garage or section is needed.
To make an environment less appealing to rats, clean up inside and outside your property. Rodents like old newspapers or magazines, boxes, rags and junk in cupboards, spare rooms and basements. In the garden, rodents like piles of bricks, timber, rubble, derelict cars or appliances, piles of green waste, and overgrown parts areas. Remember to rodent proof the compost and seal all entrances into buildings. Keep areas around houses and buildings clear as they like to travel along the edges of structures.
Cats and dogs will not usually solve a rat or mouse problem and may only be successful in catching the odd one or two.
More information
Rats are listed as a Site Led pest under the Hawke’s Bay Regional Council Regional Pest Management Plan 2018 – 2038. We do not undertake, nor are responsible for rat control in any area that is not a Priority Ecosystem site.
If you require rat control services, please contact a local pest controller. For guidance, our Biosecurity Advisors may assist you by discussing your problem and advising your best course of action.
Related links
Management Programme
Site-led Pest Programme
That the subject, or an organism being spread by the subject, that is capable of causing damage to a place is excluded or eradicated from that place, or is contained, reduced, or controlled within the place to an extent that protects the values of that place.
Unwanted Organism
An unwanted organism is any organism that's capable of causing harm to natural or physical resources (like forests and waterways) or human health. A number of introduced pests in New Zealand are classed as unwanted.
Taxonomies
FamilyMuridae
TypeAnimals
GroupMammal
HabitatLand
Management ProgrammeSite-led Pest ProgrammeUnwanted Organism
