Cluster Flies

Cluster Flies

Cluster Fly

Insect Control: How to Get Rid of Cluster Flies

Treatment includes a residual insecticide to window frames, door frames, cracks, crevices, soffit and fascia on the exterior, window frames, door frames, cracks, crevices, baseboards and attics on the interior. Treatments are generally done mid-August through mid-October in fall, and March-April in spring. Some overspray may occur on windows, so it recommended that window cleaning be done after treatment and only the window, not the frame.

How to Identify a Cluster Fly Infestation

  • Adults measure 8 to 10 millimetres in length and have light and dark grey-checkered abdomens
  • At first glance, they may look like house flies, but they are larger, darker and slower-moving
  • The name “cluster fly” is used because of their habit of gathering in clusters after entering a house in the fall
  • A fly problem becomes more obvious on days when temperatures rise and the flies become more active, gathering in windows where light attracts them

How to Prevent a Cluster Fly Infestation

  • Make sure that all screens fit properly and that there are no cracks or holes that would allow flies to enter your house
  • Weather strip windows and doors
  • Fill any cracks or crevices with caulking around doors, window frames, and other openings in the building structure

Possible Health Concerns

Cluster flies are not usually a health hazard. However, they are a nuisance, and are parasites on our earthworms.

About Cluster Flies

  • Cluster flies emerge from the ground in early fall and spring. The females lay their eggs in soil and the larvae parasitize themselves on earthworms for about 15-20 days. The larvae then move near the surface and emerge as an adult a few days later
  • They can enter a structure through any tiny openings and are simply trying to get over winter
  • They are long lived and on days where it might be particularly warm and sunny inside, they emerge, often in windows as the light attracts them