Spider spraying

When to spray for spiders in New Zealand

The best months and weather to spray for spiders in New Zealand, which product types last on which surfaces, and the order to treat eaves, frames and fences.

The short answer

We recommend spraying in late summer, roughly February into March, on a dry, still day, and again in spring if webbing is heavy. That timing lands before the autumn rise in wandering spiders and before cluster flies look for somewhere to spend the winter. A residual surface spray on eaves, window frames and fences outlasts anything sprayed indoors, and if the eaves are two storeys up, a professional spider treatment is usually the safer option.

The months spiders are most noticeable, and why

Late summer and autumn, because that is when the mature males of several species leave their webs and retreats to find a mate, and some end up indoors. Manaaki Whenua records Avondale spider males coming into houses from January to March, and Te Papa notes vagrant spider males wandering inside in autumn. Outside, webs rebuild quickly through summer while insects are plentiful.

So our recommendation is to spray in February and March, so the product is fresh when the autumn rise comes. No official source sets spray months for New Zealand; this is the timing we use and the reasoning behind it, and a mild autumn can stretch the season either way.

Weather and time of day

Pick a calm, dry day when no rain is due for at least as long as the label's rain-free period, and spray only surfaces that are already dry, so the product stays where you put it. Our own practice is mid-morning, once the dew has gone, never in wind, which carries spray onto plants and ponds, and not onto a wall baking in full afternoon sun.

Evening spraying is often suggested because spiders are active at night, but the residual is meant to sit on the surface for weeks, not to hit spiders as they move, so the time of day matters far less than dry weather and dry walls.

Product types, and how long each lasts

For the outside of a house, a residual surface spray, whether a ready-to-use trigger pack, a hose-end bottle or a concentrate you dilute, is the type that keeps working, for weeks to a few months depending on the surface. Aerosol knockdown sprays kill what they hit and stop working once dry. Foggers are a poor choice for spiders, because the mist does not reach webs and retreats.

Dusts suit wall voids and the gaps where a roof space opens to the eaves, and sticky traps tell you what is moving about indoors rather than controlling it. People often ask which brand is best; we do not rank brands, and the honest answer is that the product type, the surface and the timing decide the result more than the name on the bottle. Whatever you buy, follow the label directions exactly.

Why the surface changes how long a spray lasts

A residual product works only while it stays on the surface a spider touches, so anything that washes it off or breaks it down shortens its life: rain on exposed eaves, a house wash, strong sun on a north-facing wall, and porous surfaces such as bare timber, brick and concrete that soak it in. Painted soffits under deep eaves hold it longest, which suits spiders, since they web there.

Two practical points follow. Do not wash the house within the period the label gives after treating, and if a house wash is booked, spray after it rather than before. On walls that take the weather, expect the treatment to fade sooner, and watch for webs returning as the sign it has.

The order to do it in

Brush down webs and egg sacs first, starting high and working down, then spray the places web builders anchor: soffits and eaves, the frames of windows and doors, downpipe brackets, meter boxes, fence tops and rails, under decks and along garage door tracks. Spraying onto silk wastes product, and an egg sac left in place can hatch once the residual has faded.

Keep spray off flowering plants, where bees feed, away from fish ponds and water features, since many residual insecticides are toxic to fish, and away from children's play equipment. Webs that come back quickly in one spot usually point to a light or a gap there that is feeding or sheltering them, and fixing that does more than a second coat.

Smells, home remedies and what actually keeps spiders away

We know of no good evidence that peppermint, vinegar, citrus or conkers keep spiders away for long, and none of them affect a spider already sitting in its web. What does reduce them is fewer insects to eat, with outdoor lights switched off or changed to warmer bulbs and screens on windows, less shelter, with planting trimmed off the cladding, and taking webs down regularly.

Spiders have natural enemies too. White-tails feed on the grey house spiders that web the outside of houses, spider-hunting wasps take vagrant spiders, and birds take plenty. It is also worth remembering that spiders eat flies and moths, so the aim is fewer spiders on the house, not none.

When doing it yourself stops being worth it

When the eaves are above a single storey, when the same webs are back within a fortnight of treating, when cluster flies are also wintering in the roof space, or when you would rather not handle the product around children, pets or fish. At that point a professional treatment usually costs less than the time, product and ladder work of doing it twice yourself.

Ladder work at eave height is the part we would most like people to think twice about: a spray bottle in one hand leaves only one hand for the ladder. If flies are part of the problem, read about cluster flies in the roof space, since their timing lines up with the spider treatment.

Questions

Spider spraying questions

Can I spray spider killer inside the house?

You can, but it is rarely needed, and we do not spray living areas by default. Indoors, a vacuum removes webs and egg sacs better than any spray. If spiders keep turning up in one place, a targeted product along skirtings, inside wardrobes or in the garage, used to label directions, is enough. Keep children and animals away from anything treated until it has dried.

How often should I spray for spiders?

For most houses we suggest twice a year, in late summer and again in spring if the webbing is heavy, and more often on walls that take the rain or the full sun. The better guide than the calendar is the walls themselves: when webs start returning on a treated surface, the residual has faded there and it is time to do it again.

Does spraying kill white-tail spiders?

Partly. White-tails build no web and wander at night, so they cross treated surfaces less often than web builders do. What reduces them more is reducing the grey house spiders they eat, so treating the webbing species on the outside of the house does most of the work. We have covered white-tail spider bites and what the evidence says about them.

Will spider spray harm my bees or fish?

It can. Many residual insecticides are toxic to fish and to bees, so keep spray well away from ponds, water features, aquariums and hives, and off any plant in flower. Read the environmental warnings on the label in the shop, not at home, and if a pond or hive sits right against the house, that wall may be one to leave to a professional.

Is it worth spraying for spiders in winter?

Rarely. Spiders are less active in the cold, rain washes residuals off exposed surfaces quickly, and the product is better saved for spring. The exception is a mild, dry spell late in winter, just before spiders start rebuilding. Cluster flies are the same: by winter they are already inside, so the time to treat for them is late summer.

Sources

If you need someone

If you would rather not do it yourself

Spiders and flies

Spider & Fly Control

Most of the spiders on an Auckland house belong to two introduced web builders, the grey house spider and its black cousin, and treating the eaves, window frames and fences they web is what brings the rest down, white-tails included, because white-tails hunt them.

Read about it

More advice

Other things worth knowing

Spider bites