Cluster Fly

Get Rid of Cluster Flies in Your Home or Business

General Information

Cluster flies, commonly called attic flies, are typically found flying around the home during the fall and early winter months. Aptly named, cluster flies are usually seen in large groups.

The pests are often seen buzzing around windows or sunlit portions of the home. The insects are most active on warm days and tend to move in a more sluggish fashion than other flies.


Appearance & Identification

What Does a Cluster Fly Look Like? Cluster flies can be mistaken as common house flies. Slightly larger than house flies, cluster flies measure about three-eighths of an inch long.

Dull-gray in color, cluster flies can be distinguished by their black, checkered markings and golden-yellow hairs on the thorax. Though not regularly seen, cluster fly eggs are small, white, and oblong in shape.


Common to the New England area, cluster flies live outdoors until autumn when temperatures begin to drop. The insects then seek a safe place to overwinter until spring arrives. The pest often invades homes in search of shelter and tends to live in attics and wall voids.


What Does a Cluster Fly Eat?

During the larval stage, cluster flies feed on earthworms until they are ready to pupate. Adult cluster flies feed on fruit and nectar from flowers (sponge feeding).

The insects do not eat during the overwintering period.


The cluster fly reproductive process begins when the ground warms up in the late spring/early summer.

Female cluster flies leave overwintering sites to lay eggs in soil containing earthworms. Eggs hatch in several days, and parasitic larvae burrow into earthworms to complete their larval stage of development.

The larvae feed on the host for several days, leave the host to pupate in the soil, and then emerge from the soil as adults. When winter approaches, adult cluster flies seek shelter in dead trees, hedge rows, and the openings in man-made structures.

Problems Caused by Cluster Flies

Cluster flies do not pose any health risks to humans and cause no damage to the home.

The insects are mainly a nuisance when inhabiting a home. By sneaking in through cracks and other openings, cluster flies will fly throughout warm, often inhabited, sections of the home and bunch around windows.

Known to gather, cluster flies can be a serious annoyance when present in large numbers. The flies may also leave dark spots of excrement on surfaces they land on.

Signs of Infestation

Cluster fly infestation is apparent when multiple flies are spotted in the home.

During the winter, the pests usually hibernate in attics and inside of walls to avoid the cold and will not be detected.

When the home warms up, they can be spotted darting around the residence and grouping around windows.

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Cluster Fly Control & Prevention

The best prevention is to seal up any openings where flies may get in. Common entry points are cracks under baseboards and spaces between windows and door trim.

Once a residence is infested, cluster flies can be extremely challenging to deal with, and the best remedy is to call a local pest control professional.