The common house fly, Musca domestica, is a ubiquitous insect. Temperature stands as a primary factor influencing the activity, development, and survival of these insects. Understanding how flies react to varying thermal conditions provides insight into their behavior and population dynamics throughout the year.
The Critical Temperature Zones
House flies exhibit distinct activity levels across different temperature ranges. They are most active and thrive in warm conditions. Adult house flies show optimal survival between approximately 22.2°C and 28.28°C (72-83°F). Larval development is particularly efficient in a range of 35°C to 38°C (95-100.4°F). When given a choice, house flies tend to select environments around 30°C (86°F).
As temperatures cool, fly activity declines. Below 15°C (60°F), flies become sluggish and less active. Their overall activity at 15°C is significantly lower compared to warmer temperatures like 25°C or 35°C. Flies enter a state of inactivity or dormancy when temperatures drop to around 7-10°C (45-50°F).
At the extreme ends of the thermal spectrum, temperatures become lethal for flies. Sustained exposure above 36.1°C (97°F) can be fatal for both adult house flies and their immature stages. Conversely, adult flies typically perish when temperatures plummet to freezing or sub-zero conditions. House fly overwintering areas generally need to remain above -5°C (23°F) for survival.
What Happens When Temperatures Drop
When temperatures fall below their preferred range, house flies undergo physiological and behavioral changes to survive. Cold temperatures cause a metabolic slowdown, reducing their energy needs. This helps them conserve energy during unfavorable conditions.
Many fly species, including house flies, can enter diapause, a dormancy with suspended development and reduced metabolic activity. This allows them to endure cold periods, often in sheltered locations such as attics, basements, or natural outdoor refuges like leaf litter and soil. Flies that enter diapause may accumulate fat reserves in the fall as preparation for overwintering. Some species can even produce natural antifreeze compounds, like glycol, to tolerate freezing temperatures. Prolonged exposure to cold without adequate shelter is lethal for adults, eggs, and larvae.
As outdoor temperatures decrease, flies seek warmer, protected environments. They often move indoors through cracks or gaps around windows and doors. Once inside, they tend to congregate in warmer areas of a building, such as kitchens, bathrooms, or utility rooms. This explains their presence indoors during colder months.
Leveraging Temperature Knowledge for Fly Management
Understanding the temperature sensitivity of house flies can inform management strategies. Fly populations naturally decline during colder months. Spring often marks the beginning of a new fly season as temperatures rise.
Flies are attracted to buildings by the heat they radiate, especially as outdoor temperatures drop. On unseasonably warm winter days, dormant flies inside buildings may become active, mistaking the warmth for spring.
Applying this knowledge to management involves focusing on environmental control. Sealing potential entry points, such as cracks and gaps around windows and doors, can prevent flies from seeking warmth indoors. Maintaining indoor temperatures below approximately 24°C (75°F) can also deter flies by making the environment less conducive for egg hatching and breeding. Furthermore, consistent removal of organic waste helps limit breeding sites, as flies thrive and reproduce in warm, moist conditions where such materials are present.