As temperatures fall, the number of flies buzzing around significantly decreases. While it might seem flies simply vanish, they employ various strategies to cope with the seasonal shift, allowing them to disappear from plain sight and reappear when warmer weather returns.
How Flies Survive Cold Temperatures
Flies endure cold primarily through diapause, a pre-programmed period of arrested development and metabolic activity. Distinct from hibernation, which is a response to immediate environmental conditions, diapause suspends a fly’s growth and development, allowing it to survive unfavorable conditions like freezing temperatures or lack of food.
Many fly species enhance cold tolerance by producing cryoprotectants, compounds like glycerol or other polyols that act as natural “antifreeze” within their cells. These substances lower the freezing point of their body fluids, preventing ice crystal formation that would damage tissues. While some adult flies may perish in harsh cold, individuals in diapausing stages, such as eggs, larvae, or pupae, are often better equipped to survive.
Where Flies Go During Winter
As winter approaches, flies seek sheltered locations to enter diapause. Many common household flies, such as house flies and cluster flies, migrate indoors. They often congregate in undisturbed areas like attics, wall voids, basements, or other enclosed spaces. These indoor environments offer stable temperatures that remain above freezing, providing insulation from the external cold.
Outdoor fly species find protected overwintering sites. They may burrow into loose soil, hide under bark, or nestle within deep leaf litter. Crevices in rocks or sheltered areas beneath logs also serve as refuges. The aim is to find a location that offers protection from harsh winds and extreme temperature fluctuations, ensuring a more stable microclimate for survival.
The Seasonal Cycle of Fly Populations
Winter significantly impacts fly populations, leading to a drastic decline in active adult numbers. Many adult flies die off as temperatures drop and food sources become scarce. However, species continuation relies on individuals successfully entering diapause, surviving in dormant stages such as eggs, larvae, pupae, or even as diapausing adults.
These surviving individuals serve as the foundation for the next generation. As spring arrives and temperatures rise, the cues that triggered diapause begin to reverse. The dormant eggs, larvae, pupae, or adults become active, resuming their development. This synchronized emergence, combined with rapid reproduction in favorable conditions, leads to the swift resurgence of fly populations, completing their annual cycle.