As autumn rolls in across New Zealand, it's not just cooler weather arriving, it's also the start of cluster fly season. These sluggish pests are known for sneaking into homes and businesses, seeking out warm, hidden spots to hibernate through the winter.

While they don’t breed indoors, cluster flies gather in large numbers, often clustering around windows, wall voids, attics, and especially roof spaces. They may seem harmless, but on sunny winter days, they become a real nuisance as they re-emerge in search of light and warmth.

Why Cluster Flies Are a Problem

Cluster flies don’t pose any direct health risks, but they can cause big headaches:

• They gather in unsightly numbers.
• When crushed, they leave greasy stains on walls, curtains, and furniture.
• They return year after year thanks to pheromones they leave behind at their gathering spots.

In businesses, especially those open to the public, even a small infestation can leave a poor impression on customers.

How to Prevent Cluster Flies

The best way to deal with cluster flies is prevention, stopping them before they settle in for winter. Here's what you can do:

1. Seal Up Entry Points

Inspect your building carefully for cracks and gaps around windows, doors, vents, and eaves. Use a high-quality sealant to close them off, and fit fine mesh screens over vents to stop flies from slipping indoors.

Note:
Complete sealing is nearly impossible under iron roofing, making roof spaces one of the easiest places for cluster flies to invade.

2. Use a Light in the Roof Space

Since sealing roof spaces completely is difficult, there’s a clever trick: install a light up there. During colder months, turn the light on intermittently (for example, a few hours at night).

Cluster flies are naturally attracted to light. Once drawn in, they'll circle the light continuously and eventually die of exhaustion. It's a simple and effective way to significantly reduce fly numbers inside your roof without chemicals.

3. Maintain Outdoor Areas

Cluster flies are attracted to long grass, leaf piles, and compost near foundations. Keep lawns short, clear away debris, and secure outdoor rubbish to make your property less inviting.

Also, remember that sheds and outbuildings are favourite spots for cluster flies to nest, so check and treat these areas as part of your autumn fly-prevention plan.

If Cluster Flies Get Inside

Even with careful prevention, some flies may still find a way indoors. If you spot them:

• Avoid squashing them as they can stain surfaces and release smells that attract more flies.
• Use a vacuum cleaner for safe and easy removal. Dispose of the vacuum bag outside immediately.

Why Professional Treatment Helps

Cluster flies don’t just wander in randomly. Once they find a good hiding place, they leave behind a pheromone trail a scent that tells other flies, "this is a good spot." That’s why infestations tend to repeat in the same areas year after year.

A professional pest controller can:

• Treat affected areas with specialised products that kill cluster flies.
• Break down the pheromone trails to prevent future fly invasions.
• Apply residual repellents to help protect your home or business long-term.

By treating areas like roof spaces, attics, and sheds early, you can stop cluster flies before they become a full-blown problem.

Act Early to Stay Fly-Free

Cluster flies may seem like a small problem now, but without action, they can quickly become a major annoyance throughout winter. Preparing your home or business this autumn with sealing, maintenance, and smart strategies like using a light in roof spaces will make all the difference.

Need help managing cluster flies? Contact Southern Pest Control today for expert advice and solutions to keep your property protected all year round.

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