Cluster Fly Control in New Zealand
They don't breed in waste — so the fix isn't bait. It's sealing, cooling and vacuuming.
Every autumn and winter, thousands of Kiwi homes fill with sluggish, golden-brown flies clustering at sunny windows and in roof spaces. These are cluster flies — and they behave nothing like the house flies buzzing around your bin. Understanding the difference is the whole secret to cluster fly control, because the method that clears house flies (a bait trap) barely touches them.
What cluster flies actually are
Cluster flies are parasites of earthworms — they lay their eggs in the soil and the larvae develop inside worms in your lawn and pasture. They never breed in waste or food. When the weather cools, the adults push into the warm, sheltered gaps of a house to overwinter: roof spaces, wall cavities, around window frames and under eaves. On a sunny winter day they warm up, wake, and stumble toward the light — which is when you suddenly see dozens indoors.
Why a bait trap isn't the answer
House and blow flies are drawn to the sweet and protein baits in a reusable fly trap because they breed in waste and feed on the same things. Cluster flies are different — they feed on nectar and plant juices and have no interest in your bait. A trap will catch the occasional straggler, but it will not make a dent in a cluster fly problem. The real fix is to stop them getting in.
For the full species breakdown — identification, biology and where they hide — see our cluster fly guide.
1. Identify them
Golden-brown, slow-moving flies clustering at sunny windows and in roof spaces in autumn and winter are cluster flies — not house flies. They do not buzz around food.
2. Seal the entry points
In early autumn, seal gaps around the roof line, eaves, vents and window frames with silicone or mesh. This is the single most effective step — stop them getting in before winter.
3. Keep them cool
Cluster flies wake and fly when they warm up. Keep curtains drawn on the sunniest windows and avoid heating unused roof spaces, so they stay dormant until you can remove them.
4. Vacuum & trap stragglers
Vacuum up the flies already inside and dispose of the bag. A reusable fly trap catches the odd straggler, but sealing is what solves a cluster fly problem for good.
When to act
The timing matters. Sealing your home in early autumn, before the flies start pushing indoors, prevents the problem entirely. Once they are in the walls, vacuuming and keeping them cool manages the symptoms, but you will be playing catch-up until spring. Walk the outside of your house each March and seal the roof line, eaves, vents and window frames — one afternoon's work saves a winter of flies at the windows.
For the other flies
If you also have house or blow flies around the bin, compost or kitchen, that is a different problem and a bait trap is the answer — see our reusable fly traps and the pantry pest guide for that side of fly control.
Cluster fly control FAQs
Seal first, trap the rest
Cluster flies need sealing, not bait. For house and blow flies, a reusable trap does the work.