Borer and other pests

Borer can weaken timber. Long term, it can threaten the structure of parts of your home.

17jan borer and other pests hero 1

Borer attacks untreated and damp timber. Make sure under the floor is well ventilated to prevent this area becoming damp. For minor, or early infestation, treat the infested areas. This can be easier said than done. Replace badly affected timber.

Recognising borer

17jan common house borer 177x100

There are up to 7 species of borer in New Zealand. The most common is the Common House Borer. Signs that you may have borer in your home timbers, doors or furniture include small (2-4mm) flight holes on the surface of the timber and piles of fine sawdust.

17jan two toothed longhorn borer 161x100

The Two-Toothed Longhorn borer is a native to New Zealand and also common. It is a much larger beetle and its flight holes are larger, up to 7mm, and more oval in shape. This type of borer is less likely to be found in buildings.

Borer life-cycle

Common borer females lay up to 100 eggs on the surface of bare timber or in old borer holes. The eggs take 4-5 weeks to hatch and the larvae then bore into the wood, where they stay, chomping away for up to 4 years.

They then pupate before leaving the wood, creating holes. The adults are airborne for about a month between November and March, to mate before the cycle starts all over again.

Two tooth borer can remain in the wood for up to 11 years before exiting in autumn. Damage is usually severe from two tooth borer and timber will often have to be replaced. Because two tooth borer will also attack living trees, they can be more common in bush clad areas.


Borer like seasoned or moist untreated timber. They are often found on the south side of buildings or in floor timbers because these areas are prone to damp. They are also fond of soft (sapwood) or untreated wood and can be common in untreated native timbers in older homes. It is not uncommon to have borer attack some boards and not others – the untouched ones are probably harder heart wood.

Some wood is naturally resistant to insect attack – for example, macrocarpa. Kiln drying radiata pine improves borer resistance. Provided it remains dry, radiata is suitable for internal framing, heart quality macrocarpa and eucalypt species for weather-exposed timbers. For piles the Building Code Acceptable Solution requires timber treated to at least H5.

Using untreated wood would require an Alternative Solution under the Building Code. Speak to your timber retailer for the best option for the intended application or see NZ Standard 3602.

Sawn timber is also more prone to borer attack than a smooth surface.


Borer-infested timber can be treated, but if timbers are severely weakened you should strengthen the timber or ultimately the timber may need to be replaced.

The only long-term treatment for borer is a residual surface application of a product including insecticide or preservative. The treatment must last longer than the lifecycle of borer. This type of treatment can only be used on bare timber, so you may need to strip the timber of paint or vanish before treatment.

Airborne treatments (such as bombs, misting or fogging) will only kill the adults on the wing (November to March) and won’t stop the larvae from eating away at the inside of your timber.

If you see evidence of borer in your weatherboards, there is a good chance the borer is more extensive than it seems. This is because borer tends to attack from the inside of the boards. The only long-term solution is to replace the affected weatherboards and treat the framing timber behind while the wall is open.

Any large-scale infestation should be treated by a professional with the right safety equipment.

Furniture can be treated by fumigation by a pest control company or by injecting the flight holes. Fumigation is not usually suitable for houses or large areas as the area needs to be completely sealed. Fumigation also doesn’t provide residual protection so you will need to consider a surface treatment as well.


17jan termite 150x74

Termites are not generally common in New Zealand although there have been localised infestations. Termites live in colonies inside wood and hollow the wood out leaving thin outside layers.

If you think you have a termite infestation call the Exotic Pest and Disease Hotline on 0800 80 99 66.

Mice and rats

There is one type of mouse (the house mouse) and three types of rat in New Zealand:

  • The Norwegian or sewer rat (most common).
  • The ship rat.
  • The kiore (rare).

Mice can chew through wiring causing an electrocution hazard. They are also fond of chewing through food packaging. Rats are unsanitary and if someone complains you could get a visit from the environmental health officer.

To get rid of vermin you need to attack them on 3 fronts:

  • Clean up places they like to nest.
  • Keep them out of the house.
  • Eliminate them with poison or traps.

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 your insulation.

Keep out: Rats and mice only need a very small hole to get into your house. They can climb vertical surfaces, gnaw through walls and squeeze in through gaps around windows or doors. 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.

Wipe out: Poison baits are an effective form of rat control. Follow the instructions carefully and wear gloves when handling the bait. Protect animals and children by using a box or piece of pipe for the bait station. Keep bait down for at least 2 weeks after the last signs of activity. For mice, put down a number of stations close together as they tend to nibble a little from each.

Traps are good for catching mice, again put several close together. Rats are much more cunning and learn to avoid the traps. A way to get round this is to bait the traps but not set them for a few days so the rats get used to feeding from them. Make sure the bait is well secured when you do set the trap. Always use gloves and wash your hands after handling dead vermin.

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Member comments

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CW and DL D.
03 Oct 2020
Borer prevention - 2 or 3 tips

To stop borer infesting your woodpile and then infesting your house, manage your wood-pile well. (1) Any wood with borer holes should landfilled if it can't be burnt before the next flight season (spring-summer); usually this wood will have been dead for some time so will dry out and be burnt within weeks.

(2) The borer life-cycle is 3-5 years, so aim to burn wood in the 2nd or 3rd winter after cutting it. It will then be fully dried but any borer infecting the fresh cut surfaces will not have time to mature. Green wood stacked with air flow around and through it will dry quickly and be less unlikely to get infested.

(3)?? An old tip is to put fresh billets of poplar or other wood attractive to borer in your loft and underfloor so any borer that fly in will lay there. Replace the billets in spring of each year, and immediately burn the old billets. The snag with this approach is that they become a crowded nursery for borer if you forget to remove and burn **every** billet (or sell the house with them in place).

Bill Dashfield

Heather S.
05 Jan 2017
what do the common border look like and how big eg are they 1cm long?

I can't seem to find any continuity of pictures that I've googled. Many of the images I've seen are bugs like click beetles etc that we have in NZ. Can someone please post a picture of what most NZ borer that attack homes look like please? Consumer,ear, you really should load photos.

Previous member
11 Jan 2017
Re: what do the common border look like and how big eg are they 1cm long?

Hi Heather,

The Common House Borer is a small beetle about 4mm (1/8’’) long. It generally looks like any other common beetle, if a little smaller, i.e. round and fat with six legs and two thin antennae, and brown/copper colouring. We've now included a picture.

George - Consumer NZ staff