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  • Writer's pictureGavin Kenny

Cluster flies

Updated: Jun 13

As autumn arrives, you might notice the presence of cluster flies (Pollenia) buzzing in and around your home. These pests seek refuge and warmth indoors as winter approaches. With the arrival of spring and rising temperatures, cluster flies reemerge. To assist you in preventing these pests from overwintering in your home, we've compiled information about cluster flies.


What do they look like.

Mature cluster flies exhibit a dark gray hue, measuring approximately 1/3" to 2/5" in length. Adorned with golden hairs on their bodies, they display a distinctive checkered pattern of light and dark shades along their abdomens, complemented by a noticeable striped design behind their heads. Resembling other fly species, they feature two large eyes. In their larval stage, cluster flies present as diminutive, white worm-like creatures.


Cluster flies vs house flies.

Distinguishing cluster flies from house flies can be challenging due to their similar appearance, but there are discernible differences. Cluster flies, being slightly larger, showcase overlapping wings when at rest. Their movement is notably slower compared to the swift flight of house flies. Additionally, a key distinction lies in their behavior—cluster flies tend to congregate in sizable groups in sunlit areas, a behavior not typically observed in house flies.


Where do cluster flies live.

When cluster flies infiltrate indoor spaces, they have a tendency to seek out elevated areas within your home, such as the attic, earning them the moniker "attic flies." These pests conceal themselves in cracks, crevices, and voids. Indoors, you can discover cluster flies behind curtains, beneath clothing in closets, behind picture frames, and nestled in furniture. Primarily prevalent in Europe, North America, Australia, and New Zealand, cluster flies exhibit a preference for staying in close proximity to human habitation.


Cluster fly habits

Cluster flies belong to the same family as blow flies. Outdoors, they prefer to live close to the ground. They’re sometimes called grass flies. Adults feed on flower nectar, plant sap, fruits, and other organic material. Their larvae are parasites of earthworms. Female cluster flies lay eggs in the soil near earthworm burrows. This allows the larvae to burrow into the ground and feed on the worms.


Why are cluster flies in you're home.

The affinity of cluster flies for light becomes evident in their attraction to windows on sunny days and artificial lights during the night. Unlike many other filth flies, these insects do not exhibit an attraction to garbage or other refuse. Instead, their notable tendency to gather around sources of light distinguishes their behavior, making them less drawn to typical breeding grounds associated with other fly species.


Habits of cluster flies in summer time.

Throughout the summer, cluster flies exhibit a preference for outdoor environments. The spring and summer months mark their breeding period, during which they lay eggs. Once the larvae hatch, their diet consists of earthworms. While the majority of cluster flies are active outside during the warmer months, encountering a few inside remains possible. If these flies have overwintered in your home, they may emerge during the warmer seasons, seeking an exit to the outdoors.


Habits of cluster flies in winter time.

As overwintering pests, cluster flies actively seek shelter to evade cold weather. With the drop in temperatures, these insects congregate on the sides of homes before infiltrating indoor spaces. They gravitate towards dark areas such as attics and wall voids for refuge. After the cold weather subsides, cluster flies reemerge within homes, attempting to return to the outdoors.


Cluster flies are not dangerous.

Despite being deemed a nuisance as overwintering pests, cluster flies do not pose a threat by biting humans or animals (aside from earthworms). Importantly, they do not spread bacteria or lay eggs in food, thus presenting no health risks. The primary concern with cluster flies lies in the potential size of infestations. Due to their tendency to cluster together, these infestations can grow to significant proportions, creating challenges for homeowners.


Life cycles of cluster flies.

Typically, each season witnesses approximately three to four generations of cluster flies. As adult cluster flies emerge from their overwintering phase in the spring, they lay eggs in soil cracks. These eggs hatch within a span of 3-4 days, and the larvae then spend two to three weeks feeding on earthworms.

Following this feeding stage, the larvae enter the pupal phase in the soil, lasting for 11-14 days. Subsequently, a new generation of adult cluster flies emerges. The entire life cycle of a cluster fly, from egg to death, spans a duration of one to three months.


Will cluster flies go away on their own.

If cluster flies have entered your home during the fall for overwintering, they typically remain inconspicuous. Occasionally, they may emerge on warmer, sunny winter days, making attempts to exit through windows. During these moments, they may exhibit a lethargic, almost zombie-like state, occasionally falling to the floor as if they were dead. At times, cluster flies may appear half-dead or deceased, yet, akin to zombies, they persist if left undisturbed.


D.I.Y methods to keep cluster flies from you're home.

To ward off the arrival of cluster flies, it's advisable to implement pest-proofing measures for your house. Consider the following preventative steps:

  1. Ensure that door and window screens are in good condition.

  2. Seal any cracks, crevices, and holes on the exterior of your house, paying attention to areas around plumbing and cable penetration points.

  3. During the summer, engage in spot treatments for cluster flies outdoors using a plant-based Flying Insect Killer. This proactive approach can help reduce their populations, thereby minimizing the likelihood of them entering your home to overwinter in the fall.

We here at Pest.ie have dealth with massive cluster fly problems, from dairy farms to hotel complexs, we also deal with private domestic homes that are having cluster fly problems. So if you are having cluster fly problems, contact us.


Cluster Flies
Cluster Flies



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