A beetle remains as an egg for 7 to 10 days before hatching into the second form, the larva. They are very tiny when the first hatch, and it takes them about 3 months before they enter the next body form. However, to grow, they must shed their skin every so often. Right after they moult, their skin is white and soft, which allows the animal to grow before their skins hardens and turns tan again in a day or two. Larvae moult about 15 times and can get very big.
Large larvae are what people buy in pet stores or bait shops to feed their reptiles or fish.
When a larva has eaten enough food and grow big enough, it pupates into the third body form, the pupa. While in this form, the beetle does not eat or move very much. The pupa just sits and waits while its insides rearrange into the form needed for the fourth and final body stage. The pupal stage lasts for 7 to 10 days, and finally the pupa ecloses and becomes an adult. In the final body form, beetles look for other mealworm beetles to mate with and produce offspring to start the life cycle over again.