{"id":164,"date":"2025-08-26T20:32:09","date_gmt":"2025-08-26T20:32:09","guid":{"rendered":"https:\/\/www.frontrangepest.com\/blog\/?p=164"},"modified":"2025-08-26T20:32:10","modified_gmt":"2025-08-26T20:32:10","slug":"cluster-flies-and-other-winter-invading-flies-in-colorado-homes","status":"publish","type":"post","link":"https:\/\/www.frontrangepest.com\/blog\/cluster-flies-and-other-winter-invading-flies-in-colorado-homes\/","title":{"rendered":"Cluster Flies and Other Winter-Invading Flies in Colorado Homes"},"content":{"rendered":"\n

As temperatures drop, certain insects begin seeking shelter indoors. Among the most common \u201cnuisance invaders\u201d in Colorado are cluster flies, which often become a prominent presence in homes and buildings during the cool months. Other flies, such as blue bottle flies and the black blow fly, may also take advantage of warm, dry indoor spaces.<\/p>\n\n\n\n

What Are Cluster Flies?<\/strong><\/h2>\n\n\n\n

Cluster flies (Pollenia<\/em> species) are slightly larger than house flies, dull grayish-brown, and often have golden, tangled hairs on their thorax. Unlike filth flies, they do not develop in garbage or decaying matter. Instead, their larvae are parasites of earthworms, feeding on them in soil before emerging as adults.<\/p>\n\n\n\n

Cluster flies are most common in areas with moist soil, irrigated lawns, and nearby waterways, and they are particularly prevalent in higher-elevation Colorado communities. Adults are active outdoors from spring through autumn, but as the days shorten in late summer, they begin seeking warm, sheltered spots indoors for the winter.<\/p>\n\n\n\n

How Harboring Pests Invade Homes<\/strong><\/h2>\n\n\n\n

From mid-August through early October, cluster flies gather on sun-warmed walls and can enter buildings through tiny cracks around windows, vents, or siding. Once inside, they cluster in wall voids, attics, and other quiet spaces, entering a semi-dormant state called diapause. Dormant flies do not reproduce indoors and remain largely inactive until spring, though some may wander into living areas, creating a nuisance.<\/p>\n\n\n\n

Other Common Winter-Invasive Flies<\/strong><\/h2>\n\n\n\n