Where do flies go in the winter? Do they die, fly to warmer climates, or hibernate?

When winter arrives and temperatures drop, many wonder what becomes of the flies that seem so ubiquitous in warmer months. While some flies do die off with the cold, a significant number of them, particularly common house flies and cluster flies, employ a clever survival strategy: they enter a state of dormancy, often referred to as diapause, which is similar to hibernation. This allows them to endure the harsh conditions until spring.

Flies are cold-blooded insects, meaning their body temperature is regulated by their environment. As it gets colder, they become lethargic and seek out sheltered spots to ride out the winter. They often find their way into homes and other buildings, drawn to the warmth. Common overwintering locations include attics, basements, wall voids, sheds, and even under tree bark or leaf litter. These spaces offer a dry, relatively warm, and undisturbed environment where they can safely reduce their metabolic activity and conserve energy.

During this dormant period, flies can survive for several months, burning very little energy. Some species, like cluster flies, are known for gathering in large numbers in attics and wall voids, which is why you might suddenly see them emerge on a surprisingly warm winter day, mistaking it for spring. They might even produce a natural "antifreeze" in their bodies to help them withstand freezing temperatures. When spring finally arrives and temperatures consistently rise, these flies will become active again, emerging to restart their life cycles.