As colder weather arrives, the buzzing of flies diminishes, leading many to believe these insects vanish or die off. However, flies possess remarkable strategies to endure harsh winter conditions, seeking sheltered locations to survive until warmer temperatures return.
The Science of Fly Hibernation
Flies do not truly hibernate in the same way some mammals do, entering a deep, prolonged sleep. Instead, many fly species undergo a state known as diapause. Diapause is a genetically programmed state of suspended development and reduced metabolic activity, triggered by environmental cues such as decreasing temperatures and shorter daylight hours. During diapause, the fly’s growth and reproduction are halted, and their physiology undergoes changes to enhance their tolerance to cold, such as accumulating cryoprotectants. This physiological adaptation allows flies to conserve energy and withstand unfavorable conditions like extreme cold and a scarcity of food resources, enabling them to persist through winter, emerging once conditions become hospitable in spring.
Typical Hibernation Locations
Flies choose specific sites to enter diapause, seeking places that offer protection from the elements and relatively stable temperatures. These locations can be both outdoors in natural environments and indoors within human structures.
Outdoors, flies commonly seek shelter in natural features that provide insulation. They might burrow under loose tree bark, find refuge within dense leaf litter, or bury themselves in the soil. These natural covers act as barriers against freezing temperatures and strong winds, allowing the flies to remain dormant until spring.
Indoors, human dwellings offer attractive overwintering sites due to their stable, warmer temperatures and numerous secluded spots. Cluster flies (Pollenia rudis) are a common nuisance in homes, congregating in attics, wall voids, and other protected areas. These flies often enter buildings in late summer or early autumn, drawn to sun-warmed walls before finding small openings to infiltrate. Similarly, face flies (Musca autumnalis) also overwinter as adults in structures like attics, wall voids, and basements. Once inside, these flies typically aggregate in clusters to conserve heat and energy, often found in quiet, undisturbed spaces such as attics, wall voids, basements, or around windows.
Preventing Indoor Hibernation
To prevent flies from establishing hibernation sites within your home, proactive measures are important as autumn approaches. Sealing potential entry points is a primary strategy. Inspect the exterior of your home for any openings around windows, doors, utility pipes, and foundation. Use materials like silicone caulk or expandable foam for openings.
Ensuring that window and door screens are in good condition is also important; repair any tears or holes. Installing door sweeps on exterior doors can help block entry. Additionally, proper ventilation in attics and crawl spaces can reduce moisture, making these areas less appealing for flies. If flies have already entered, a vacuum cleaner can effectively remove visible aggregations. For cluster flies, cleaning their previous hibernation spots with disinfectant may help remove the scent they use to return annually.