Why Are Big Black Flies in My House?

Big black flies, commonly known as cluster flies, can be cause for concern if they are buzzing around inside your house. While this large fly species is more of a nuisance than a legitimate threat, cluster flies are unpleasant, and the only effective removal remedy is to either trap or kill them. Getting and keeping these big black flies out of your home, though, is much easier if you first understand why they are there.

Cluster flies, which are part of the ​Pollenia​ fly genus, are slow-moving and parasitic in nature. While a housefly or blowfly spends most of its time landing on, feeding on, and laying eggs in food or dead animals, cluster flies are less attracted to these landing spots.

Generally during warm summer months, cluster flies are primarily concerned with laying eggs and breeding more larvae or maggots outdoors. They target underground areas rich with earthworms, which their maggots then feed on. These big black flies only seek refuge indoors during cooler months. In these winter months, they are especially attracted to hibernating in attic spaces and the openings in between your walls. They can also lay clusters of eggs in these spaces, which will hatch when the weather warms. If cluster flies lay eggs in your home during the winter months, the heat from your heater can also mimic a summer atmosphere, prompting these eggs to hatch.

Luckily, because this large fly species is less interested in eating and reproducing on food and dead animals, specimens which often carry disease, they pose a much lower risk of spreading contaminants than other fly species you might find indoors. Still, cluster flies can be relentlessly annoying and a sign that something is wrong with your house. Whether some structural issue has developed or you and your family are engaging in a pest-attracting behavioral pattern, take their presence as a sign to search for issues.

Cluster flies inside your house had some entry point. One of the most common ways big black flies enter your house is through broken roof shingles, siding holes, or torn window screens. Conducting a thorough inspection of your home's entire exterior is a great way to spot and seal any unintended openings.

While these large black flies are not necessarily attracted to food, sugar will entice them. Make sure you are keeping everything sugary in your kitchen and pantry in well-sealed containers to keep these pests from finding their way into your goodies.

Stopping cluster flies from entering your house starts with targeting areas in your yard where they may also be congregating. In cooler months, these large black flies often lay eggs in abandoned wooden structures or piles of debris. Clearing items like these out of your yard will help deter these flies from breeding near your home, making it less likely that they'll find their way inside. Keeping your yard free of debris is also a great way to deter other pests, like rats and raccoons.

These big black flies also thrive around pools of standing water. If you have any puddles of water around your property, these may be attracting unwanted flies. If at all possible, finding ways to drain these water sources will make your property less hospitable.