Cluster flies, also known as attic flies, are household pests. Adults measure 8 to 10 millimeters in length and have light and dark grey-checkered abdomens. The thorax of an adult cluster fly is covered in short, golden hairs and the wings overlap when at rest. Cluster flies are slightly larger and darker than the common housefly and move more sluggishly.
They appear on the sunny side of the structure in heaviest concentrations in late fall and early winter, as they seek warm locations in which to live during cold months. Although cluster flies are observed buzzing and congregating at windows, screens may prove ineffective in preventing their entrance. Cluster flies are capable of crawling through small openings in the walls of a structure. They hibernate in secluded parts of houses like attics and wall voids. On sunny winter days, the wall voids become warm and the cluster flies try to move toward light. Very often they find themselves in the inhabited parts of the house and the move to the windows. They cluster around the windows and they leave stains on walls and curtains if crushed.
Cluster flies are commonly seen congregating at windows. Although it would seem that the use of window screens might help to eliminate the chances of infestation, cluster flies are capable of entering homes through small cracks and openings in walls and foundations.
The best way to repel flies is through simple, preventive measures. Flies prefer warm temperatures and are most active from late spring to early autumn. In order to best repel flies during this time, limit access to your home as much as possible, keeping doors and windows closed. You may also choose to screen windows (as mentioned before, this might not work), doors and vents. Keep garbage cans clean and securely closed. Keeping surfaces clean will make your home less appealing to flies. You can apply Scraminator where flies may be harboring, traveling, breeding or entering the structure.
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