Cluster Flies

Cluster flies are non-metallic gray in color with golden hairs on their thorax. They are 8 to 10 mm in length. Cluster flies closely resemble house flies, but are larger and slower. Unlike the house fly, the wings of the cluster fly overlap when they are at rest.

Habits & Behaviour

Cluster flies are the most common fly found in properties during the cool months. Cluster flies are known to enter residential,  recreational/cottage, and commercial properties in “clusters” during the late summer/early fall months in search of a protected place to overwinter in secluded areas such as in wall voids, attics, closets, and empty rooms usually in upper regions of the premises.

They can enter the home through the tiniest crevices around door and window frames, but also through any other small unsealed opening. Once inside, while it is cold they are dormant. On very sunny days, even in winter, they may become active and sometimes will be found flying around the premises. They are frequently found at windows because sunlight attracts them. In the spring, cluster flies leave their overwintering sites to breed.

Complaints & Destruction

Because of their unusual developmental habits and the ability to heavily infest a property, cluster flies are also one of the trickiest pests to control. Cluster flies primarily enter properties up high through soffits and facia, gable ends, dormers, vents, and flashing. They will also enter through cracks and crevices between bricks, stones, siding, around windows and doors, and other tiny openings in the structure. Once they are inside a property, cluster flies can cause allergies if in large numbers, attract secondary pests such as larder beetles, provide food for secondary pests, leave stains on walls and draperies, and cause an unpleasant odour.

Major Risks & Dangers

Although they do not bite, sting or carry disease, cluster flies can be a major nuisance and infestations can significantly get out of control if not professionally excluded.

Reproduction & Life Cycle

In the spring, adult cluster flies emerge from their overwintering sites, mate and lay eggs in cracks in the soil. After hatching, the tiny maggots search out their earthworm hosts. The life cycle of a cluster fly from egg to adult requires about 28 days. Three to four generations per year are possible.

Eating Habits

The adult flies feed on the nectar of flowers

Treatment & Prevention

To eliminate and reduce the risk of cluster flies invading your residential,  recreational/cottage, or commercial properties, treatment and exclusion is the best prevention.

Greenshield Pest Control Inc. can provide you with many treatment, exclusion and prevention solutions.


If you suspect a cluster fly infestation within your residential,  recreational/cottage, or commercial properties, it is best to let the professionals do the job of safely removing the insects. Please contact us today or see our Pest Control Services section for further information on the types of services and insect pest solutions we can provide

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