• Cluster flies are about 3/8" in length.
  • They are a gray fly that carries its wings back together.
  • They become a nuisance in fall when they over winter by the thousands in structures.
  • They breed in earthworms in the soil and eliminating their breeding site is not a control method.
  • When at rest these flies are slow and bumble about the room.
  • Finding entry and excluding them is the best option for control cluster flies.


  • Exclusion is the main control method for cluster flies.
  • On warm winter days inspect exterior perimeter on the south and south west sides of the structure. Note where cluster flies are getting in. Seal all areas where cluster flies may gain entry.
  • Use insect light traps to help control adult flies.