It’s normal to see big black flies buzzing around bins or flying past your head in warmer months. But spotting these flies indoors during the fall or winter can be confusing and frustrating. These seasonal intruders are usually cluster flies.
Unlike house flies, cluster flies tend to appear in large numbers, especially in attics, wall voids, around light fixtures, under eaves, or around windows. Homeowners often report cluster flies in the house all of a sudden, especially on warmer winter days when the indoor heat wakes them from dormancy.
If you’re dealing with a cluster fly infestation, you’re not alone. Our technicians know how to get rid of cluster flies and help you protect your home long-term. For tailored cluster fly control, contact us today and schedule a free property inspection.
A cluster fly is actually a general name for a number of different flies in the genus known as Pollenia. A cluster fly looks a lot like a common house fly. They are approximately seven millimeters long, and black. They have large reddish eyes and a thorax that is covered with short hairs.
Cluster flies are even more common in Europe, but they likely came to the United States via international shipping. Since they lay eggs and their larvae are parasitic on earthworms, it’s even possible they came in a shipment of worms.
As with many flies, the life span of a fly in the cluster fly family can vary depending on environmental conditions, but their tendency to overwinter indoors allows them to survive through colder months.
Cluster flies and house flies may look similar at a glance, but there are key differences. Cluster flies are slightly larger, fly more slowly, and tend to move in groups; hence the name. Their bodies have a golden sheen due to tiny hairs, while house flies are typically dull gray with red eyes.
Behavior also sets them apart. House flies are active year-round and are drawn to food and waste, often buzzing around kitchens and bins. In contrast, cluster flies do not seek out food in your home. Instead, they enter to overwinter and become most noticeable on sunny winter days when they emerge and gather around light sources.
Cluster flies come out during the fall and winter months and look for a place to overwinter. This means they essentially hibernate until the months get warmer. So, what attracts flies like cluster flies to your home? These pests look for places to shelter where they can stay relatively warm, such as inside the walls of your home. They are also known as "attic flies,” which gives you some idea of one of their other preferred hiding spots.
Cluster flies can crawl into the smallest spaces and then find a place to hunker down. Once inside, they stay dormant until indoor heating or warmer outdoor temperatures wake them. That’s why you might notice cluster flies in the house all of a sudden, even in winter. Their presence doesn’t mean your home is unclean; it just means it’s a comfortable place for them to hide.
Spotting a few flies might not seem like a big deal, but multiple flies in specific areas can indicate a cluster fly infestation. Here are common signs to look for:
If you notice these signs, it may be time to call in the cluster fly pest control experts at Ehrlich to help prevent further problems.
The best way to stop a cluster fly infestation is to prevent them from getting in. Like with other pests, making sure that all cracks and spaces are sealed in your home’s siding, near where the roof meets walls, roofing tiles, and screens that lead into attics or provide access to spaces between walls and siding.
Of course, one of the best ways to get rid of cluster flies is to get your home treated before winter arrives by a trained fly control technician. Ehrlich has the tools and knowledge to spot places where cluster flies can get in and where they might like to hide. Our technicians can then provide your home with a treatment plan to help remove cluster flies and other pests from using your home as their winter vacation spot.
Call now to book your free inspection.
Some homeowners try fly traps to catch adult flies. Light traps or sticky flypaper may help reduce visible numbers. However, these methods rarely address the root issue, such as flies hiding inside walls or attics. DIY insecticide sprays or vacuuming may help with surface-level issues, but they don’t prevent re-entry. For long-term fly control, it's best to call in trained technicians.
If you’re facing recurring problems, calling in a cluster fly exterminator may be your best option. Our team has the experience and training to locate fly entry points, identify high-risk areas, and create a plan tailored to your home.
Using professional fly exterminator services services helps address the infestation at the source and limits the chance of a recurring infestation next season. We'll work with you to keep your home protected and reduce the chance of future cluster fly problems.
Long-term cluster fly control starts with prevention. Start with exclusion: keep screens in a good condition, seal gaps around the home, and schedule seasonal inspections—ideally before fall. Reducing outdoor lighting at night may also limit fly attraction.
Unlike many other flies, cluster flies are not drawn to food waste or garbage and are not known to spread disease. While their presence can be annoying, they’re less unsanitary than house flies.
Cluster flies lay eggs in soil, not in homes. The larvae live off earthworms in a parasitic stage before becoming adults. So, although they’re a nuisance, they don’t typically cause harm to people or pets.
Cluster flies live outdoors in the warmer months, which can explain why you might only notice them at certain times of year. During the summer, cluster flies lay eggs outdoors in cracks in the soil. These eggs quickly hatch, and the larvae are parasitoids on earthworms. Typically, cluster flies are not noticed outdoors in the summer.
As temperatures drop in the fall, adult flies search for warm spaces to overwinter. Homes, especially those with high elevation or lots of sun exposure, often attract them. The tallest structure in the area may have more cluster fly issues than the surrounding, lower structures. They gather in groups and crawl into cracks around windows or rooflines. Cluster flies do not lay eggs or breed indoors; they are only looking for shelter from winter weather.
Inside, they stay dormant until warmer outside temperatures or heating systems wake them. This is when many homeowners see a sudden appearance of cluster flies.
No, cluster flies do not bite or sting. They don’t feed on blood and are not considered dangerous to people or pets.
Adult cluster flies feed on flower nectar and other plant-based materials outdoors. Unlike house flies, they are not attracted to garbage, food, or waste inside your home, which makes them less likely to contaminate surfaces.
An adult cluster fly can live up to several months, especially if it successfully overwinters indoors. Most of their lifespan is spent in a dormant state during the colder seasons, with activity picking up again as temperatures rise.
No, cluster flies do not lay eggs inside homes. Instead, they lay their eggs outdoors in soil. When the larvae hatch, they seek out earthworms, which they parasitize during development. Indoor sightings are of adult flies only, not flies emerging from eggs indoors.
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