Flies exhibit seasonal patterns in their presence and activity, influenced by factors like temperature, day length, and resource availability. This insect seasonality refers to periodic changes in their behavior, physiology, and population levels.
Why Flies Are More Common in Warm Weather
Flies thrive in warm, moist environments, which significantly accelerates their life cycle and population growth. As temperatures rise, their metabolic rate increases, speeding up their development from egg to adult. For instance, a house fly’s development from egg to adult can be greatly shortened in hot environments, taking approximately 7-10 days. This rapid progression through the egg, larva, pupa, and adult stages allows for multiple generations to emerge within a relatively short period, leading to exponential population increases.
Warm weather also brings an abundance of food sources and suitable breeding grounds. Flies, including house flies and blowflies, reproduce in decaying organic matter, food waste, and animal remains. These materials decompose faster in higher temperatures, providing richer nutrition for fly reproduction. Furthermore, humidity levels, which often accompany warm weather, are suitable for egg hatching and larval development, contributing to the surge in fly numbers.
How Flies Survive Colder Months
When temperatures drop, flies employ various strategies to survive periods of cold or unfavorable conditions. Many species enter a state called diapause, which is a period of suspended development and reduced metabolic activity. This physiological state is often triggered by decreasing temperatures and shortening day length, allowing flies to conserve energy and withstand harsh conditions. Diapause can occur at any stage of the fly’s life cycle, including as eggs, larvae, pupae, or even adults, depending on the species.
Some flies overwinter in sheltered locations, actively seeking refuge from the cold. For example, adult house flies may find shelter in refuse tips where fermenting waste maintains a continuously high temperature. Cluster flies (Pollenia species) commonly seek out dry, sheltered areas like attics, wall voids, or barns to spend the winter in a dormant state. Their activity levels significantly decrease in cold temperatures, as they are cold-blooded.
Understanding Seasonal Fly Behavior
The observable patterns of fly presence throughout the year reflect their survival strategies and environmental dependencies. Fly activity typically begins to increase in spring as temperatures rise above 60°F, prompting emergence from overwintering sites. Their populations generally peak during the summer months due to optimal conditions for reproduction and development. This is when they are most active and noticeable around homes and outdoor spaces.
As autumn approaches and temperatures cool, outdoor fly populations noticeably decline. Some species, like cluster flies, begin to seek indoor refuge in homes and buildings for overwintering, congregating in sheltered areas. While many adult flies may perish with the onset of extreme cold, the survival of eggs, larvae, or pupae ensures the emergence of a new generation in the spring. This seasonality can vary by region; in tropical climates, flies might be active year-round, while temperate zones experience distinct seasonal patterns.