Flies hatch from eggs and grow into larvae. They shift into the pupa phase before growing into adults. The birth cycle of a fly takes 10 days.
Female flies lay an average of 900 eggs in a lifetime. Females lay the eggs in safe places, such as crevices and corners. Females also hide them in materials that provide sustenance for the young, including decaying matter. Flies emerge from the eggs as maggots within 24 hours and begin to feed. Maggots molt after two days; in this process, invertebrates get rid of their exoskeletons to form new ones.
The flies go through multiple molting stages, growing larger after each session. Upon the third molting session, they burrow deep into their feeding areas, and their skins harden into a shell as they enter the pupa stage. During this process, they grow wings and legs to become adults, and they form bumps on the head to break out of their shells. Once they emerge as flies, the bumps shrink back into their heads.
After two or three days, female flies are able to reproduce. Adult flies have three months to reproduce before expiring. The average lifespan of a fly is 21 days since this insect has to contend with a wide array of predators.