Undergoes transformation from larval body form adult fly. Small white maggots emerge from the eggs and set about eating as much as they can. Pests Wildlife Dropping Like Flies Announce University Of Nebraska Lincoln Pupa to emergence takes 10 days. How long does it take maggots to turn into flies . So there is about two weeks or about 15 days between the maggot-stage and the appearance of the adult-fly. They vary depending on the species and the temperature. How long does it take a maggot to turn into a fly. We usually see them in this first stage while they are still 3-9 mm long and whitish in color however they can grow to be 20 mm. I would recommend waiting until they consume the corpse and then they will disappear as will the odor. This trash bin should be lined with a disposable plastic bag and lidded to prevent odor which may attract flies and prevent flies from entering the bin. A basic cycle that begins with an egg then develops through a larva phase a pup...