Cluster or Attic Fly Facts & Information

How to Identify & Control Cluster Flies

Latin Name



What Do They Look Like? Cluster Fly Cluster Fly image licensed under CC

Cluster flies, also known as attic flies, are household pests.

    • Length: Adults measure 8 to 10 millimeters.
    • Body: Light and dark gray-checkered abdomens. The thorax of an adult cluster fly is covered in short, golden hairs and the wings overlap when at rest.
    • Characteristics: Cluster flies are slightly larger and darker than the common housefly and move more sluggishly.

How Did I Get Cluster Flies?

Cluster flies are capable of crawling through small openings in the walls of a structure. These flies enter homes looking for overwintering sites during the cold months. Cluster flies prefer warm areas, so homeowners often find them flying around houses on sunny days in the winter and late fall months.


Entering living spaces by way of electrical outlets or baseboards, the pests take shelter in attics and walls to hibernate, awaiting the arrival of warmer spring weather. On sunny winter days, the wall voids may become warm and the cluster flies will try to move toward light. Although cluster flies are observed buzzing and congregating at windows, screens may prove ineffective in preventing their entrance.

How Serious Are Cluster Flies?


Cluster flies do not carry diseases and will not cause extensive damage to homes. However, the pests may darken walls or windows with their droppings and may attract other insects if they die inside the wall voids. Large numbers of the flies often congregate on windows and inside ceiling light fixtures, making them a nuisance to residents.

How do I get rid of cluster flies?

What Orkin Does

Your local Orkin technician is trained to help manage cluster flies and similar pests. Since every building or home is different, your Orkin technician will design a unique program for your situation.

Orkin can provide the right solution to keep cluster flies in their place...out of your home, or business.


Life Cycle

The cluster fly life cycle begins when a female lays her eggs in the soil in late summer or early fall. These eggs hatch within a few days, after which larvae seek to enter the body cavities of earthworms.

What Do They Eat?

Cluster fly larvae feed on earthworm hosts for several days, at which time they molt and pupate in the soil.


Cluster flies' development time from egg to adult is about 27 to 39 days.