Cluster Flies

Cluster flies are sluggish, gray insects slightly larger than house flies, distinguished by their golden hairs on the thorax and tendency to move slowly. These pests are commonly found in rural areas during summer, living outdoors and feeding on flower nectar, but become problematic in fall when they enter buildings in massive numbers to overwinter. Cluster flies gather in wall voids, attics, and other secluded areas, emerging on warm days and leaving greasy spots when swatted. Control focuses on exterior treatments before fall entry, sealing cracks and crevices, and professional intervention for severe infestations due to their overwhelming numbers.