About The Pest
Cluster flies are parasites of earthworms and include several species of overwintering blow flies. During late summer and fall, adults enter structures to overwinter. They do not eat or contaminate food areas or harm people or possessions. They are simply a nuisance pest. They will gather in large numbers in nooks and crannies of unoccupied spaces. Resembling large house flies, they buzz about windows on warm days late winter through early spring.
Cluster Flies peak during the months of August through October.