Fruit Fly Life Cycle (IMAGE) Washington University in St. Louis Caption Fruit flies go through a whole series of transitions between life stages, as shown here. The larval molts are called instars. The mature larva forms a prepupa, and then a pupa, which undergo metamorphosis to produce the adult. Existing in both grub-like and winged forms allows the fly to maximally exploit ephemeral food sources without tying its fate to them. Credit Flybase Usage Restrictions please credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.