Mealworms go through four life stages: They start life as an egg, hatch into a larva, eventually turn into a pupa, and finally emerge as adult beetles.
Egg: The egg stage is too small to see. In the mealworm container, the egg blends in with the grain and poop.
Larva: The larval stage is the one we know as the mealworm. It looks like a worm except for the six small legs close to the front of its body. When they first hatch, the larvae are too tiny to see. They grow until they are too big for their hard exo-skeletons; they shed these skins, growing a little each time, for about 5 months.
Pupa: When they’re ready, the larva will crawl to the surface of the grain substrate and change into a pupa. The pupa doesn’t move and doesn’t eat. In captivity, the pupa must be removed or it will be eaten by both the larvae and the adult beetles. They stay in the pupa stage for about two or three weeks.
Adult: After weeks of major internal changes while existing as a pupa, the adult beetle emerges. It changes colour over the first two weeks of its life from pale beige to dark brown. The beetles are unremarkable; they look like a textbook drawing of themselves. They don’t bite or fly, and they don’t move very fast.