Cluster Fly Control: Protect Your Home


What Do Cluster Flies Look Like?
image of a cluster fly
Size: With an average size of 5/16 of an inch, adult cluster flies grow slightly larger than the common house fly.

Color: The body of the cluster fly is largely nonmetallic gray with black markings.

Characteristics: Some distinguishing characteristics of the species include a pair of wings, longitudinal black lines on the thorax and yellowish hairs that give off the appearance of a golden sheen.

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  • A pervasive nuisance in homes and other man-made structures during the fall and spring, cluster flies overwinter to survive the drop in temperature.
  • Prevalent pests in the Mid-Atlantic region and other parts of the United States.
  • Cluster fly larvae are parasites of earthworms but tend to cause little damage outside of their parasitic behavior.
  • Given their tendency to congregate in large numbers, cluster flies may require the attention of pest control professionals.


What Do Cluster Flies Eat?
Larvae feed on earthworms as they develop into adults. Once fully developed, cluster flies feed on:

  • Organic matter
  • Plant sap
  • Fruit
  • Flowers
  • Feces
  • Proteins in animal meat


Female cluster flies lay eggs in cracks in the soil during the late spring and summer months. Within three days, the eggs hatch and the emerging maggots eat their way into an earthworm where they will go through the larval and pupal stages of the cluster fly life cycle.

The entire developmental process lasts an average of 27 to 39 days. As such, cluster flies are able to produce three or four generations each year. Adult flies live for several months.


  • Look for clusters of adult flies in the home around late autumn and early spring.
  • Check for small, dark spots of excrement on windows and walls.
  • May notice the emergence of adults during brief warm spells in the winter months.

Problems Caused by Cluster Flies

Surprisingly, the cluster fly causes very few problems. Though they overwinter in large numbers, the insects do not:

  • Feed on cloth
  • Nibble holes in furniture
  • Cause any sort of structural damage

Furthermore, the species waits until summer to lay eggs and does not feed on human food.

Though previous research suggests that large numbers of cluster flies can cause problems in hospital settings, the insects are not known to carry diseases of medical importance to humans.

Instead, the cluster fly is merely classified as a nuisance rather than a pest insect.

Signs of Infestation

Cluster flies get their common name from their tendency to congregate in clusters on the sunny exteriors of buildings in the fall and on windows inside the home on warm winter days.

As such, the sight of large congregations of flies around windows during unseasonably warm weather is a fairly certain indicator that a cluster fly infestation exists somewhere in the home.

Residents should check for the insects in:

  • Nooks
  • Dark corners
  • In wall cavities
  • False ceilings
  • Attics

In addition to congregating in large groups, cluster flies leave behind small, dark spots of excrement on walls and windows which serve as further evidence of an infestation problem.

Furthermore, once the weather becomes consistently warm in the spring, cluster flies will emerge from their overwintering sites and begin to appear around the house. Typically, emerging flies move sluggishly and will clumsily fly around homes looking for a way outside.

Prevention Tips

Prevention remains the best method of dealing with cluster flies, as it is challenging to remove them from the home once they find a place to overwinter. Exclusion works best, so homeowners should take care to seal cracks around:

  • Windows
  • Doors
  • Siding
  • Utility pipes
  • Behind chimneys
  • Other similar locations

Replacing damaged window screens also helps to prevent a cluster fly infestation.

Tips for Removal from Home

  • Cleanliness: Homeowners may vacuum up adult cluster flies and dispose of them in a sealed container to prevent the nuisances from escaping and finding a way back inside. However, this method almost never eradicates the problem completely.
  • Call an expert: To effectively handle an infestation of cluster flies, residents should contact a pest management professional to aid in the application of insecticides to help reduce the number of flies one may experience. Contact Western today for a free inspection.

Learn more about Western’s comprehensive Home Pest Control Plans.

Call for service: (877) 250-3857