Borer library

When borer fly in New Zealand, beetle by beetle

Borer spend most of their lives hidden in timber, and the few weeks they spend outside it are when they are easiest to notice and the season every treatment plan works around. Knowing the months helps whether you are booking a borer inspection, planning treatment or buying a house in winter.

Updated 6 October 2026

In New Zealand the common house borer is out mostly in November, December and January, occasionally from October to March. The two-toothed longhorn emerges in autumn or early winter. Huhu fly from November to early March, peaking from mid-December to late February, and powderpost beetles usually emerge in October and November. Northern Hemisphere calendars do not apply here.

Treatment is usually timed ahead of the emergence of the beetle involved, and an inspection reads fresh signs in the light of the season.

When do borer fly in NZ, month by month?

Each beetle keeps its own season, so the calendar depends on which one is in your timber. The table brings together the months published by the NZ Farm Forestry Association, Consumer NZ and a manufacturer's technical sheet. Where they disagree, the core months come from the forestry leaflets and the wider range from the other two sources.

Borer flight calendar for New Zealand (core months: NZFFA leaflets; wider range: Consumer NZ and a manufacturer sheet)
Month	Common house borer	Two-toothed longhorn	Huhu	Powderpost
January	Main flight	–	Peak	–
February	Some, wider range	–	Peak	–
March	Some, wider range	Autumn emergence	Until early March	–
April	–	Autumn emergence	–	–
May	–	Autumn emergence	–	–
June	–	Early winter, tailing off	–	–
July to September	–	–	–	–
October	Some early emergence	–	–	Usual emergence
November	Main flight	–	Starts	Usual emergence
December	Main flight	–	Peak from mid-December	–

The common house borer's wider range is where the sources part ways. The forestry leaflet records adults from November to January; Consumer NZ has them in the air between November and March, and the manufacturer's sheet gives exits from October to February. Expect most activity in early summer and some at either end.

Why are overseas borer calendars wrong for New Zealand?

Because many are written for the Northern Hemisphere, where late spring and summer fall between about May and August. Some overseas pages give April to July for the common furniture beetle, which in New Zealand is autumn and winter, the wrong end of the year. Use calendars written for New Zealand, or translate the season rather than copying the months.

The season names travel; the months do not. A guide that says borer emerge in late spring and early summer is, translated to New Zealand, describing roughly November to January.

When should borer treatment be done in NZ?

Ahead of the emergence of the beetle you have, so the product is in place before adults chew out and lay the next round of eggs. For common house borer that points to late winter and spring, before November. For the two-toothed longhorn it points to summer, before autumn. Bombs and foggers are the exception: they target adults, so they are used during the flight months.

Residual surface products, injectors and borate preparations act on the timber and the larvae and are less tied to the calendar, but having them in place before the flight season means the timber is protected when adults look for somewhere to lay. What a full treatment involves is on the treating live borer page, and the guide to borer bombs and sprays explains what each product reaches.

Does the season change what a borer inspection can see?

It can. Fresh dust and clean, pale holes are the strongest signs of live borer, and they are most likely to appear during and soon after emergence. A house inspected in winter may show less fresh dust from common house borer than it would in January, so an absence of new dust at that time of year is weaker evidence that the borer has stopped.

That does not make a winter inspection pointless. Hole edges, old dust, timber condition and moisture can be read at any time of year, and the longhorn emerges in autumn and early winter. It does mean a buyer should read a no-activity note in the light of the month it was written. For how reports word this, see borer in a building report.

How can you tell borer beetles are flying in your house?

Small brown beetles gathering on windowsills or in the corners of rooms in early summer are the usual sign of common house borer emerging, and new holes, often with a little fresh dust beneath, appear at the same time. Large beetles drawn to outside lights on summer nights are more likely huhu, while longhorn adults shun light and are seldom seen.

Keep a beetle or two in a jar and note where and when you found them. With the hole size, that narrows down which beetle you have before anyone treats anything. The guide to house borer by build year covers which houses are most likely to carry the common borer.

Questions people ask

What month should I bomb for borer?

During the flight months, when adults are out of the wood. One manufacturer sets its fogger for October to March, and Consumer NZ places house borer adults in the air between November and March. A bomb outside that window has few adults to hit. It never reaches larvae, so pair it with a product on bare timber or an injector in finished timber.

How long do adult borer beetles live?

Not long. A manufacturer's technical sheet says common house borer adults die within three to four weeks of emerging and eat no more timber: their task is to mate and lay eggs. Almost the whole life cycle, three to four years, is spent as a larva inside the wood, which is why the larvae are what treatment has to reach.

Do borer fly in winter in NZ?

The common house borer and the huhu do not; their adults are out from late spring to early autumn. The native two-toothed longhorn differs: it emerges in autumn or early winter, so oval holes with fresh dust in May or June can be a live sign. Powderpost adults usually appear in October and November.

Is a winter borer inspection reliable?

It is reliable for what can be seen at any time: hole type, timber condition, moisture and old damage. It is weaker on activity for common house borer, because fresh dust is less likely between flight seasons. If activity matters to your decision, ask how confident the activity call is. The pre-purchase borer inspection page covers timing around your conditions.