The lifespan of a fly can vary depending on the species and environmental conditions. Generally, the lifespan of a fly ranges from a few days to several weeks.

One of the most common species of fly, the housefly (Musca domestica), has an average lifespan of around 28 days. However, this can vary depending on the conditions in which they live. In warmer temperatures, the housefly may have a shorter lifespan of around 8-10 days, while in cooler temperatures, it may live up to 2 months.

Other species of fly have different lifespans. For example, fruit flies (Drosophila melanogaster) have a shorter lifespan, with females living an average of 39 days and males living an average of 49 days. Blowflies (Calliphoridae) have a longer lifespan, with some species living up to 2 months.

The lifespan of a fly is affected by several factors, including temperature, humidity, food availability, and predation. Flies are ectothermic, meaning that their body temperature is regulated by their environment. As a result, they are particularly sensitive to temperature changes. In warmer temperatures, their metabolism increases, and they require more food and water to survive. In cooler temperatures, their metabolism slows down, and they may enter a state of hibernation or diapause to conserve energy.

Food availability is also important for the lifespan of flies. Flies require a source of food and water to survive, and a lack of these resources can shorten their lifespan. In addition, flies are attracted to decaying organic matter, such as garbage, animal feces, and rotting fruit. If they are unable to find these sources of food, they may not survive for long.

Predation is another factor that can affect the lifespan of flies. Flies are preyed upon by a variety of animals, including birds, spiders, and other insects. In addition, parasites such as mites and parasitic wasps can also affect the lifespan of flies by feeding on their tissues or laying eggs inside their bodies.

Overall, the lifespan of a fly is relatively short, and they have evolved to reproduce quickly and in large numbers to ensure the survival of their species. Despite their short lifespan, flies play an important role in ecosystems as decomposers and as a food source for other animals.