Cluster Fly


Actual Size: 8 mm

Characteristics: Non-metallic; dark-gray.

Legs: 6

Wings: Yes

Antennae: Yes

Habitat: Gravitate toward ripe fruit and flowers. Often overwinter inside buildings.


  • Slightly larger than houseflies.
  • Will hibernate and overwinter inside homes in New Jersey.
  • Unlike blowflies, cluster flies are not attracted to human foods.

Cluster Flies in North Jersey

Cluster flies, which belong to the blow fly family, are common in the United States. They don’t like cold weather, so they enter homes in the fall to hibernate and can be numerous in hard-to-reach areas like wall cavities, attics, and false ceilings. When spring arrives and they try to leave their hibernation site, they frequently become lost and end up in living spaces. Cluster flies are annoying, but they’re not as annoying as many other nuisance fly species. They tend to be more sluggish and do not fly around loudly inside buildings.

Cluster Fly Habitat

Cluster flies’ natural habitats are outdoor areas near flowers and ripe fruit. When temperatures drop, they seek shelter inside homes and buildings to survive winter. They seek areas where they can easily be concealed — dark corners, nooks, underneath clothing in closets, behind curtains, in wall voids, and behind pictures and furniture. When spring arrives and temperatures warms up, they may emerge from hibernation and not be able to find their way back outside.

Cluster Fly Behaviors, Threats, or Dangers

Cluster flies are not considered a significant threat to human health. A big part of why is that they do not have an affinity for human food. However, cluster flies can be bothersome as they often travel in large swarms of thousands, hence the name. During the fall, adult flies search for warm shelter where they can spend the winter. During their hibernation period, their accumulated excrement can create an unpleasant odor and may also stain walls and fabrics. When killed, they leave an oily residue.

If you are facing a cluster fly infestation, reach out to your local north Jersey fly control specialists!