Flies are a common nuisance during warmer periods. Their activity diminishes with changing environmental conditions, rather than them vanishing completely. Understanding the factors influencing fly populations explains their seasonal presence and decline.
Seasonal Decline of Flies
For many common fly species, their numbers begin to noticeably decrease as temperatures drop, typically in late fall or early winter in temperate regions. This reduction is a gradual decline, not an abrupt disappearance. In many areas, this means a significant decrease in fly activity from October to November. Flies are less active when temperatures fall below 7 degrees Celsius (45 degrees Fahrenheit). However, some species may remain active in mild or temperate climates throughout the winter, taking advantage of favorable conditions to continue breeding and foraging.
Environmental Factors at Play
The primary environmental reasons for the seasonal decline of flies are closely tied to temperature, daylight hours, and food availability. Flies are cold-blooded insects; their body temperature is regulated by their surroundings. As temperatures decrease, their metabolism slows, making them sluggish and eventually inactive. When it gets too cold, they are unable to fly. This reduced activity impacts their ability to find food, reproduce, and survive.
Shorter daylight hours also signal the approach of colder seasons, influencing their behavior. Additionally, the availability of food sources, such as decaying organic matter and animal waste, diminishes outdoors during colder months. These combined environmental shifts compel flies to seek shelter or enter a dormant state, contributing to their reduced presence.
Understanding the Fly Life Cycle
During colder months, flies employ various strategies to survive. Many species enter a dormant state known as diapause, which is similar to hibernation. In diapause, their metabolic activity is significantly reduced, allowing them to conserve energy and withstand harsh conditions. This can occur at different stages of their life cycle, such as eggs, larvae, or pupae, often in sheltered locations like soil, compost piles, or within buildings.
Some adult flies may also overwinter by finding refuge in warm, secluded spots like attics, wall voids, or refuse tips. While their typical adult lifespan is short, around 15 to 30 days, the life cycle stages can be prolonged significantly in cooler temperatures. For example, the larval stage, which typically lasts 3 to 5 days in warm conditions, can extend up to 8 weeks in cooler temperatures, and pupal development can take up to four weeks in temperate climates. When warmer conditions return, these dormant stages or overwintering adults re-emerge, restarting the active life cycle.
Minimizing Fly Presence
While flies naturally decline with the onset of colder weather, individuals can implement strategies to minimize their presence, especially during peak seasons or if they persist indoors. Maintaining good sanitation is a primary deterrent, as flies are attracted to food waste, garbage, and decaying organic matter for feeding and breeding. Regularly disposing of trash in sealed containers, cleaning food spills promptly, and rinsing recyclables significantly reduces attractants.
Sealing entry points into homes is an effective method to prevent flies from seeking indoor shelter. This includes ensuring window and door screens are in good repair without tears or gaps, and installing weather stripping or door sweeps to block openings at the base of doors. For persistent issues, deterrents such as fly traps or essential oils like eucalyptus, peppermint, and lavender can help repel or capture flies.