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Flies Library

Learn About Cluster Flies in Ontario – Identification, Behaviour & Risks

Cluster Fly 

Appearance: Slightly larger than a house fly (8–10 mm). Dark gray body with golden hairs on the thorax and overlapping wings at rest.

Habitat: Common in rural and agricultural areas. Seeks shelter in attics, wall voids, and upper stories of buildings to overwinter.

Behaviour: Sluggish indoors during winter and early spring. Does not breed inside homes.

Risk to Humans: Harmless; does not bite or spread disease. Mainly a nuisance when present in large numbers.

Interesting Fact: Cluster fly larvae are beneficial in nature—they parasitize earthworms during their development.

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