Cluster Flies

Common signs include:

• Slow-moving flies gathering near sunny windows
• Groups of flies in upper rooms or attics
• Buzzing sounds in walls or ceilings
• Dark spots on window frames
• Activity increasing during warm winter days

We use a multi-step process designed for seasonal pests:

• Dust and powder treatments inside attics, wall voids, and ceiling areas
  • Liquid treatments around window frames, cracks, and entry points
  • Sealing and exclusion of gaps around siding, soffits, windows, vents, and rooflines
  • Vacuum removal for visible clusters around windows
  • Seasonal prevention in late summer or early fall

Cluster flies cannot be controlled effectively without sealing entry points.

Although cluster flies do not spread serious diseases, they can:

• Leave dark fecal spots on surfaces
• Contaminate areas where they gather
• Cause allergies or irritation when present in large numbers
• Contribute to poor indoor air quality when they die in wall voids

Their presence often signals poor sealing or ventilation.

Cluster flies enter homes to overwinter. They are attracted to:

• Warm walls, attics, and ceilings
  • Tiny cracks around siding or roof edges
  • Sun-facing upper floors
  • Unsealed windows or vents

Older buildings in New Westminster, Vancouver, and Burnaby commonly experience this issue.

We recommend:

• Sealing cracks around windows, siding, and soffits
• Repairing damaged screens
• Installing fine mesh over vents
• Improving attic insulation and ventilation
• Requesting fall prevention treatments

Fall preparation is the key to long-term control.

They do not damage structures but may:

• Stain walls and windows
• Create unpleasant odors in attics
• Attract other pests that feed on dead flies

Often yes.
Because cluster flies are seasonal, fall and spring visits are recommended for long-term success.