Updated: 10 Dec 2007

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Introduction

Summer means warmth and sun ... but it can also be high season for pests.

Pest infestation can be a serious problem, causing damage to your property and your health. Rats, mice and introduced cockroach species can spread diseases like salmonella and listeria.

Our Pest by pest guide looks at some of the most common household pests, and how to prevent and eradicate them.

Pest by pest guide

Act fast to get rid of unwelcome visitors. Common household pests in New Zealand are hardy and active. Female cockroaches can lay up to 40 eggs in one go and the resulting nymphs become adults in as little as six weeks. It'll cost much more to fix a problem if you leave it until the pests are established in your house.

Here's how to recognise, prevent and eradicate some common pests.

Rat (Rattus rattus; Rattus norvegicus).

• Size: 20-27cm long (excluding tail).
• Food: Prefers cereal, but will eat anything.
• Clues: Rat droppings (12mm long); gnawed wires; greasy smears along walls and floors; scratching noises in the roof or wall voids.
• Problems: Rats contaminate food and spread disease. They can also damage electrical wiring and plumbing pipes.
• Prevention: Over summer, fill in holes in your walls and use thin wire mesh to cover vents. Get rid of rubbish around your home and clear up any spillages in the kitchen. It also helps to pick up fallen fruit from trees on your property.
• Eradication: Rats are suspicious of traps; it's best to use poison baits. You can buy baits from supermarkets and DIY stores like Mitre 10. Wear gloves when putting down the bait. If you have pets or children, place the bait at the end of some plastic piping (rats can squeeze through a gap the size of a thumb). Keep putting down the bait for up to two weeks after the rats have disappeared. Call in a professional promptly if DIY baits fail as rats reproduce rapidly.
• Cost: $20 (rodent poison); $12 (rat trap); $150-$250 (professional eradication).

Mouse (Mus domesticus).

• Size: 7-9cm long (excluding tail).
• Food: Cereals, chocolate and food scraps.
• Clues: Mouse droppings (5mm long); scratching noises in lofts and basements; greasy smears along the walls of a room.
• Problems: Mice spread disease, contaminate food and gnaw electrical wiring.
• Prevention: See "Rat" above.
• Eradication: Place traditional traps along walls or on a route frequented by the mouse. Use peanut butter or chocolate to bait the traps (mice can take or leave cheese). Make sure that you release any mice a kilometre or two away from your house if using a humane trap. Baiting (as in "Rat" above) is also effective.
• Cost: $20 (rodent poison); $8 (mouse trap); $150-$250 (professional eradication).

Cockroach (Blattella germanica; Blatta orientalis; Periplaneta americana; Drymaplaneta semivitta).

• Size: 12-15mm long.
• Food: Anything, everything.
• Clues: Dead cockroaches; an obnoxious smell (particularly around warm, damp areas).
• Problems: Cockroaches spread disease and contaminate food.
• Prevention: Cockroaches thrive around hot-water cylinders and ovens; so plug all cracks and crevices in those areas. Good hygiene is essential: they'll happily dine on any food scraps you leave lying around.

Flea (Ctenocephalides felis; Ctenocephalides canis).

• Size: 1-4mm long.
• Food: Blood (preferably your pets).
• Clues: Rover or Fluffy constantly scratching. You may notice you've got small red bite marks too.
• Problems: Flea bites are a nuisance. And on some people's skin they can cause serious irritation.
• Prevention: Start with your pet - you can use flea collars, powders, or drops to stop fleas from becoming a problem. Ask your vet for the most suitable product. (If you use flea powder on a dog or cat, it pays to leave them outside for a few hours after treatment.)
• Eradication: Treat both your pets and your home. Tumble-dry any infested bedding and clothes for 45 minutes. Vacuum regularly around the edges of rooms and under furniture.
• Cost: $19 (permethrin spray); $100-$260 (professional eradication for entire house).

Common house borer (Anobium punctatum).

• Size: 3mm long (native two-tooth borer is bigger).
• Food: Untreated timber (especially damp, softer woods in older houses and antique furniture).
• Clues: Borer leave small (1.5-2mm) "flight" holes on the surface of infected timbers.
• Problems: Borer can weaken timber. In the long term they can threaten the structure of your home.
• Prevention: Make sure your sub floor is well-ventilated. To prevent borer spreading to other areas of your house, you may have to replace badly affected timber.
• Eradication: The only long-term treatment for borer is a residual surface application of an anti-borer insecticide. The treatment must last longer than the borer's lifecycle. This type of treatment can only be used on bare timber, so you may need to strip off any paint or varnish first.
• Cost: $50 (5L borer concentrate); cost of professional eradication depends on extent of borer infestation.

Fly (Musca domestica; Calliphora vomitoria).

• Size: 6-12mm long.
• Food: Food scraps, compost and manure.
• Clues: Buzzing adult flies; maggots on decaying food.
• Problems: Flies are unsanitary and ruin food. They're also annoying.
• Prevention: Flies thrive in warm, moist environments. Eliminate breeding areas by cleaning up in the kitchen and disposing of food in a covered rubbish bin.
• Eradication: Spraying adult flies with fly-spray is still effective. Shut all windows and doors in a room, and spray towards the roof. Leave the room closed up for a few hours once you've sprayed. A continuing fly problem will need a professional.
• Cost: $5 (fly spray); $100-$200 (professional eradication for entire house).

Ant (27 exotic species; 11 native species).

• Size: 2-3mm long.
• Food: Sweet foods (such as sugar and syrups).
• Clues: Ant trails leading into your house; the bodies of fallen worker ants strewn over bench-tops. You'll also find the odd live ant left behind in your sugar jar.
• Problems: Some ant species bite, but the major problem is the sheer number of the critters. They swarm on pantries and wreck foodstuffs - even packages of food that look sealed.
• Prevention: Don't leave out sweet foods. Make sure spillages get tidied up. Clean your bench surfaces with lemon juice, soapy water or diluted tea tree oil. Paint entry points with a permethrin spray. You can also lure ants away from your pantry with bait stations (available from your local supermarket).
• Eradication: Don't spray the nest. Attacking the ants like this can cause some newly introduced species to branch off into new colonies - or, in the case of Argentine ants, to re-group and form a super colony. Instead try a food-bait (one that contains boric acid, indoxacarb or fipronil). Place the bait around the nest, the workers take the bait back to the queen bit by bit, and because there's no perceived threat the nest doesn't scatter. You can buy sprays and gels from DIY stores, but be sure to follow the instructions on the label. Pay close attention to crevices and cracks around damp areas when using a spray or gel. Call an expert if the infestation hasn't improved after the initial DIY treatment.
• Cost: $8 (ant bait); $150-$300 (professional eradication for entire house), $14 (gel bait); $120-$250 (professional eradication for entire house).

Professional exterminators

Pest exterminator Jon Thomson (right) backed his car out of the driveway before fumigating the house: "The infestation was so bad that it was the only way to avoid being swamped when the cockroaches fled."

Jon has worked for Rentokil for 21 years and has a swath of horror stories to tell. But it's the cockroaches that stick in his mind: "There were about 30 cockroaches under the baby's pillow in the crib. It was pretty disturbing."

Hiring a professional

You'll need to call a professional exterminator to deal with established pest infestations. The bonus is that you can go grab a coffee while someone else deals with the creepy crawlies.

There are many pest extermination companies in the yellow pages - and there's a trade association as well. Members of the Pest Management Association of New Zealand have technical training in pest eradication. You'll find a nationwide list of registered technicians and companies on the association's website: www.pmanz.co.nz.

The association may also be able to help you if you're not satisfied with work carried out by one of its registered technicians.

Approved handlers

Pest exterminators working with substances that are toxic to humans or the environment must be approved handlers under the Hazardous Substances and New Organisms (HSNO) Act 1996. They apply to become handlers through the Environment Risk Management Authority. HSNO-approved handlers have demonstrated the necessary knowledge, safety skills and practical experience to handle potent pesticides.

Ask a pest exterminator whether or not they're a qualified handler before hiring them.

Invading hordes

Animal pests arrived in New Zealand alongside humans. Kiore (the Pacific rat) was introduced by Maori in the 10th century; since then it's been all downhill for New Zealand's ecosystems. Hundreds of other exotic species arrived on European ships in the 19th century and are now firmly established.

Our native plants and animals evolved without the threat of exotic predators and browsers. They're poorly equipped to deal with - for example - possums, wasps and stoats.

Some of our most destructive pests were deliberately introduced into New Zealand. Rabbits were released by Captain Cook in 1777 for food and fur. When rabbits got out of hand, 19th-century farmers released weasels and stoats to deal with them. Stoats kill up to 15,000 North Island brown kiwi each year, or 60 percent of that year's chicks.

Pest-free zones

But populations of our native species can regenerate quickly if they're given a chance. The Karori Sanctuary in Wellington is one of 10 essentially "mammalian pest-free" zones on the New Zealand mainland. The 225-hectare valley is ringed by a predator-proof fence that's 2.2m high. The fence is made of a woven galvanised wire mesh. In eight years, only mice and a solitary weasel have managed to get into the sanctuary.

Fifteen native species have been released back into the valley including kiwi, hihi, tuatara, and saddleback. These endangered New Zealanders are now re-established in the valley. Conservation scientist Raewyn Empson says that "many of these species are regarded as nationally endangered or threatened, and establishing breeding populations in the sanctuary has helped improve their conservation status."

The valley teems with bird life, and some of the success has flown beyond the sanctuary walls. "We've noticed an increase and spread throughout Wellington of birds like tui that were previously rare or missing from the area."

More information

• Department of Conservation: www.doc.govt.nz
• ERMA: www.ermanz.govt.nz
• Karori Sanctuary: www.sanctuary.org.nz
• Pest exterminators: www.pmanz.co.nz

Report by Luke Harrison