How does the fly life cycle progress from egg to adult?

The life cycle of a fly (order Diptera) is characterized by holometabolous metamorphosis, which consists of four distinct stages: egg, larva, pupa, and adult.123

• Egg: The cycle begins with the egg stage. While most flies lay eggs, some species, such as tsetse flies and certain parasites, hatch the egg internally and give birth to a mature larva.1
• Larva: The larva is morphologically distinct from the adult and is primarily adapted for growth and feeding. Larvae often occupy different habitats than adults, which helps reduce competition for resources. In most flies, the larva undergoes a series of molts.132
• Pupa: During this inactive, nonfeeding stage, the insect undergoes a major transformation. Larval tissues break down, and adult structures—such as wings, eyes, and legs—develop. The pupa may be protected by a cocoon or a puparium, which is a hardened case formed from the final larval skin.435
• Adult: The adult emerges from the pupa, often using specialized structures to expand its body and wings. This stage serves as the primary period for reproduction and distribution.61