Mealworms are the larval form of the mealworm beetle, Tenebrio molitor, a species of darkling beetle. Like all holometabolism insects, they go through four life stages: egg, larva, pupa, and adult. Larvae typically measure about 2.5 cm or more, whereas adults are generally between 1.25 and 1.8 cm in length.
he mealworm beetle breeds prolifically. Mating is a three-step process: the male chasing the female, mounting her and inserting his aedeagus, and injecting a sperm packet. Within a few days the female burrows into soft ground and lays eggs. Over a lifespan, a female will, on average, lay about 500 eggs.
After four to 19 days the eggs hatch. Many predators target the eggs, including reptiles.
During the larval stage, the mealworm feeds on vegetation and dead insects and molts between each larval stage, or instar (9 to 20 instars). After the final molt it becomes a pupa. The new pupa is whitish, and it turns brown over time. After 3 to 30 days, depending on environmental conditions such as temperature, it emerges as an adult beetle.