Mealworms are the larval stage of the mealworm beetle, scientifically known as Tenebrio molitor, a species of darkling beetle. They undergo complete metamorphosis with four distinct life stages: egg, larva (mealworm), pupa, and adult beetle.

• After hatching from eggs, mealworms grow and molt multiple times during the larval stage.
• Eventually, the mealworm molts into a pupa, an inactive stage where it does not eat and transforms internally.
• After the pupal stage, which lasts from about one to three weeks depending on conditions, the insect emerges as an adult darkling beetle.
• The adult beetle initially has a soft, light-colored exoskeleton that hardens and darkens over several days.
• Adult beetles then mate and lay eggs, continuing the life cycle

In summary, mealworms turn into darkling beetles after completing their pupal stage.