The lifespan of a fly is generally 15 to 30 days. Flies prefer temperatures between 75 and 80 degree Fahrenheit, so the warmer the environment, the longer the lifespan. The common house fly lives about a month when outdoors.
Flies are extremely prolific in their short lifespan. All flies develop in four stages: eggs, larva, pupa and adult. In the span of a week, a female adult fly generates about 150 eggs at a time. This process is repeated five or six times over the course of a lifetime. Within one day, maggots emerge from the eggs, form shells to pupate and within seven to 10 days, they hatch as adult flies that are capable of replicating the reproduction cycle a few days later.