Here's what you need to know about ridding your home of rodents.
Pitter-patter of rodents keeping you awake? We look at your options for getting rid of them and what not to buy.
From $1 to $15
With tunnel: From $25
The good old-fashioned snap trap is a cost-effective option for dealing with rats and mice. You can pick up a snap trap for as little as $1 and they can be set repeatedly. They can be a humane way to quickly kill rats and mice, as long as the snap bar is strong enough to crush a rodent’s skull. If you find an injured rodent, it’s time to buy a new trap.
For outdoor use, you’ll want to set your snap trap in a tunnel. A tunnel, made from plastic or wood, puts the trap out of reach of other curious creatures and protects it from the weather. A wooden trap plus tunnel will set you back about $35, but you can get plastic tunnels with a trap for as cheap as $25. The tunnel design is simple so if you’re handy with a hammer you could save a few bucks and knock one up yourself.
Depending on where you live, you may be able to get a free or subsidised trap and tunnel through Predator Free groups (see “Predator Free 2050? Maybe”).
From $12 to $20
Local company Nooski makes rodent traps that fire a rubber ring, like a docking ring, around the animal’s neck. Like a snap trap, it needs resetting every time it’s activated. They come with up to a dozen rubber rings. Refill packs of 20 rings cost $5 to $6.
The Nooski rat trap was tested by Landcare Research in 2007. It found the trap killed rats effectively and in less than three minutes. However, the trap’s design has changed since then. Nooski said it hadn't tested the new trap in lab conditions but the change was to the release mechanism that fires the ring, not the way the rat is killed.
From $4 to $44
Don’t want the little guys sharing your home, but can’t stomach killing them? Live traps catch a rodent but leave it caged. However, unless you have a pet snake, you'll still have a furry problem to deal with.
Live traps should be checked daily, as a captured rodent can be distressed and die from starvation or dehydration.
From $60 to $100
Electronic traps aim to give a rodent a fatal electric shock. They can be an effective and humane way of killing rodents, provided the current is strong enough to kill quickly. These traps can be mains- or battery-powered and need a little bait to lure the rodent into the tunnel. They’ll keep killing until the batteries run out. Some come with an indicator light to show if you’ve got something, so you only have to check and reset once it’s caught a rodent.
The traps aren’t cheap and are also not suitable for use outdoors unless they’re in a sheltered area such as a carport.
Usually used outdoors, Goodnature traps are self-resetting, a boon if you don’t want to deal with emptying and rebaiting a trap. When a rat investigates the lure inside the trap, a CO₂-cylinder powered bolt is triggered, crushing its head. The rat falls out and the trap resets.
The CO₂ cartridge and lure lasts about six months, depending on the number of times it’s fired, before they need replacing. Some traps come with a counter so you know how many of the vermin have been dispatched. You might not see the carcass – it may be scavenged by other animals.
The traps are pricey compared with a basic snap trap. But they’ve been extensively tested by the Department of Conservation (DOC) and thousands have been rolled out in conservation areas.
Poison blocks from $4.50 (80g) and bait stations from $9 to $48
Bait is an effective and relatively cheap way to deal with rodents. You can get baits in blocks, pellets or as powder or paste. You should ensure all bait is placed in a bait station and follow any safety guidelines on the pack.
There are several poisons available from hardware stores. While the active ingredients vary, most are anticoagulants. This type of poison causes internal bleeding resulting in cardiac, respiratory and kidney failure and the animal eventually dies from blood loss. It can take several doses before a rat or mouse ingests enough to kill it, and it can be ill for several days before it dies.
If you can, find and discard the bodies. Poisoned rodents scavenged by other animals, such as birds or cats, can cause secondary poisoning.
Electromagnetic and ultrasonic pest control devices are marketed as “environmentally friendly”, safe for pets, and effective – just plug in and watch the rats scurry from your home as though being called by the Pied Piper.
Electromagnetic devices claim to use your home’s wiring to create electromagnetic pulses that will drive rodents out. Manufacturers of ultrasonic models claim the devices create high-pitched sounds, inaudible to people, which drive away rats and mice.
Sounds like a wonderful, mess-free solution. But there’s a lack of evidence to show they’re an effective means of rat and mice control. None of the companies selling these devices, which cost anywhere from $20 to $300, provided us with robust, independent research showing the devices to be effective.
There are several published research papers to suggest ultrasonic devices have at best a temporary effect on rodents. The Department of Conservation tested ultrasonic devices as a potential stoat control measure, but found them ineffective – with one stoat even napping near a device.
Plug-In Pest Free (NZ), which sells an electromagnetic device, claims it’s been scientifically tested and proven to “rid premises of rats and mice”. It promises the device will give you a “genuine pest-free home, and prevent pests residing and breeding within your premises”.
But neither Plug-In Pest Free (NZ), or the Australian manufacturer of the device, Pest Free Australia Pty, were willing to share test results with us, stating they were intellectual property.
Pest Free Australia Pty was taken to court by the Australian Competition and Consumer Commission for its advertising. The court case was dropped in 2004, on the proviso the company stopped saying its products would, among other claims, stop pests nesting and breeding and permanently rid a premises of pests.
However, 16 years later, both Pest Free Australia Pty and Plug-In Pest Free (NZ) claim the devices will give you a “genuine pest free home” and stop rats “residing and breeding”.
In 2015, the Commerce Commission reminded Plug-In Pest Free (NZ) about its obligation under the Fair Trading Act to substantiate its claims.
Rival company Pestrol claims its electromagnetic and ultrasonic pest control devices make it “almost impossible” for rats to breed and build their nests, and ensure the critters vacate. Pestrol sent us some research, but none of it showed the devices were an effective means of rodent control. The company said it stands by its products.
Newfield, importers of the Sonic Guard and Ultimate electronic pest control devices said there were limitations with the devices. A Newfield spokesperson said rodents can become acclimatised to the ultrasonic sound, so it’s good practice to switch them on and off and move the device around. This is noted on the packaging.
Horticom managing director Tim Johnson, which imports Big Cheese and Times Up devices, said the devices should be used as part of an arsenal of products to control rodents in the home. “You will get rodents on the move with plug-in devices, but you still need to kill them, or in the case of live traps, move them on.”
Pest Management Association of New Zealand executive officer Peter Barry, who’s been in the pest control business for more than 30 years, said the traps were "frowned upon" in the industry.
If you hate the idea of dealing with rodents at all, you could call in the professionals.
Pest management companies usually deal with mice and rats by laying both bait and traps. A good company will take more than one visit to do it. It should come back after a week to check traps and rebait.
There is no legal requirement for pest control operators to hold a qualification, but they do need one for handling certain poisons (because of potential impact on the environment). An operator should be able to give you product safety sheets covering the substances they’re using.
The Pest Management Association of New Zealand lists its members on its website. To join, the company or technician must have an urban pest control qualification and public liability insurance.
Don’t be shy about inquiring about an operator’s qualifications and experience. We’d also recommend getting a few quotes.
There is one type of mouse (the house mouse) and three types of rat in New Zealand: the Norway or sewer rat (most common); the ship rat (also known as the black rat); and the rarer kiore.
To eliminate vermin, you need to attack them on three fronts:
Clean out: Mice like to nest in old newspapers, cupboards (airing or kitchen), spare rooms, insulation, basements and behind the oven or fridge. Outside you’ll find mice and rats in piles of rubbish, old cars, building materials or overgrown gardens. Trees that overhang eaves can let rats into your ceiling space – the ship rat likes to nest in insulation.
Keep out: Rats and mice can climb vertical surfaces, gnaw through walls and squeeze in through gaps around windows or doors. Make sure to seal holes around pipes with metal or cement; make sure doors and windows fit tightly; and put in fine wire mesh across holes into basements.
Trap smart: Set more than one trap and set them along walls. Check traps often. Pre-baiting – leaving out unconditional food so the pest builds up confidence around the trap – may help. Make sure you’re using the right-sized trap for your target. If it’s too big or too small, a pest could be injured or escape.
A dollop of peanut butter or a little beef jerky? What about aniseed or cinnamon lures? A 2016 Victoria University study showed free-ranging rats would choose cheese, milk chocolate, Nutella and walnuts over standard peanut butter. They’re especially drawn to fat.
Rodents carry diseases that can be passed on to humans. Wear gloves when emptying and resetting traps.
The government’s set a goal of being rid of rats, stoats and possums by 2050. The councils are on board, and local environmentalists have taken to backyard trapping with enthusiasm.
There are thousands of community trapping groups all over New Zealand and, with the help of council and philanthropic funding, they’re providing free and subsidised traps.
There are no national numbers showing how successful the groups have been. But, as a snapshot, a collective of more than 100 groups in Northland have caught and killed nearly 230,000 pests in the past 5 years.
However, the work may be a drop in the bucket of what’s needed.
Landcare Research pest control expert Bruce Warburton says while the predator-free goal is technically possible, it’s unlikely with the current resourcing and technology.
“We’ll never have sufficient funding with our current tools, which is why there’s an interest in new genetic-based tools.”
Pest eradication projects on islands are being tackled with poison at the moment, which is expensive but effective, but wouldn’t be okay on mainland New Zealand, he says.
A 2016 report in the NZ Journal of Ecology in 2016, which Warburton co-authored, puts the cost of pest eradication at $32 billion.
The government will put $10.5 million into Predator Free 2050 over the next 4 years.
To find a community trapping group near you, visit predatorfreenz.org.