Cluster flies are one of the challenging pests to deal with in the Southland region. Due to their unusual biology, once they infiltrate a place they like, they attract other flies to join them. Unfortunately, this means it’s notoriously difficult to get rid of cluster flies. But by knowing a bit more about them and how they behave, you can increase the chances that they won’t become a pest for your property.

What are cluster flies?

Cluster flies are the species Phormia rudis, part of the blowfly family Calliphoridae. Many flies are attracted to human food and scraps, which is why flies are often found around dishes. Cluster flies, however, survive off earthworms so tend to make their nests around earthworm burrows.

You can tell a cluster fly from other fly species by lines on their head, gold hairs on their thorax, dull grey and dark colour on the body, and their size, about 7mm-15mm long. They’re a bit slower and larger than the common housefly and are sometimes known as “dopey” flies. The flies tend to gather in large groups or “clusters” in places like the attic.

A single cluster fly

The most common time for cluster flies to appear is autumn going into early winter. Once the outside temperatures get too cold, they search for a warmer environment–usually indoors. They sleep when it’s colder. So on warmer days of the cold months, it might seem like they suddenly appear, but more likely is that they were already in the property but become active with the warmth.

The problem with cluster flies

At first glance, these pests might seem fairly easy to beat. They’re large, slow, and are fairly immobile. The problem is in their biology.

When cluster flies find a place to make their home, they release a potent pheromone that attracts more flies. And this pheromone is extremely difficult to remove. Even after strong chemical cleaners, the pheromone persists in a weaker form and can attract flies for some time after; even years later sometimes. The best way to keep them out is to make sure they never enter in the first place.

How do you prevent cluster flies?

Unlike with many kinds of insects, insect screens offer little protection against cluster flies. This is because they are more likely to get into a property by crawling through small openings.

For prevention, start by first and foremost filling in any holes in on the sunny side of the building. Then move around to the rest of the building from there. If there are no entry points they can crawl through, they’re unlikely to make an appearance. Regular chemical treatments on the roof and exterior of the property can also stop them from entering.

What’s the best way to get rid of flies?

There are a few things you can do if you notice clusters of the flies in your home. First, the cluster needs to be sprayed down with pesticide. This will kill the existing flies. The flies should then be vacuumed away or removed completely in another way.

Next, the area needs to be cleaned thoroughly with a strong disinfectant. Anywhere with the pheromones would need to be treated. If they only seem to be in a single room, wipe down as many surfaces in that room as you can.

After this, you should search the outside of the property to see where they may have come in from. Spray the disinfectant on any holes you find, especially on surfaces the sun hits. This will reduce the chance of them coming in through those same places. If they were grouped in one part of the house, search the outer walls near that area more thoroughly.

If you do everything correctly, you should see the flies start to disappear. They’ll instead head to a property that’s easier to enter and is less protected. If you still can’t get seem to stop them, feel free to give us a call or fill out the form below to get a free quote from our experienced pest control team.