What insect's larvae are commonly sold as 'mealworms'?

The larvae commonly sold as “mealworms” are darkling beetles, especially the yellow mealworm beetle Tenebrio molitor. The familiar worm-like feeder insect is therefore a beetle larva, not a worm in the biological sense.

Mealworms pass through complete metamorphosis: egg, larva, pupa, and adult beetle. The larval stage is the commercially familiar mealworm. After several molts, the larva forms a pale pupa and eventually emerges as a dark brown or black adult beetle.

They are widely raised as food for reptiles, amphibians, fish, birds, and small mammals, and are also used as fishing bait. Because they thrive on bran, oats, and other grain products, they can become pests in stored-food facilities. Their high protein and fat content has also made them a subject of research into animal feed and human food.

“Darkling beetle” identifies the beetle family, while Tenebrio molitor identifies the standard yellow mealworm species. Related beetles, including Tenebrio obscurus, may be sold under names such as mini mealworms or dark mealworms.