Mealworms that birds, reptiles, and other animals love aren't really worms. They are the larvae of darkling beetles. There are over 20,000 different types of darkling beetles and mealworms come from the species Tenebrio molitor.
A darkling beetle experiences complete metamorphosis which means that it has four distinct stages of life. The four stages are egg, larva, pupa, and adult. The amount of time a darkling beetle spends in each stage can vary greatly due to environmental factors like temperature, humidity, food, and water.
The first stage of life is spent as an egg. The white bean-shaped egg is tiny and about the size of a speck of dust. The egg is sticky and is quickly concealed by dirt, dust, and substrate. It will take around one to four weeks for an egg to hatch and the larva to emerge.
The second stage of life lasts about eight to ten weeks and is spent as a brown larva. This is the stage where the insect is a mealworm. When first hatched, it is quite small but will grow to one to one and a half inches long. Since it has a hard exoskeleton, the worm will need to molt and shed its hard outer shell in order to grow. Molts will occur ten to twenty times during this stage of life. A recently molted worm will be soft and white, but the exoskeleton will quickly harden. A mealworm spends its time eating and growing in order to save up energy for the next transformation.
During a mealworm's last molt it will turn into a white alien-like pupa. It has no mouth or anus so does not eat. It does have leg and wing buds, but they do not function. The pupa is quite helpless and the only movement it can do is wiggle. This stage of life will last one to three weeks as the pupa transforms its organs and body into an adult.
The final stage of the insect's life is as the darkling beetle and lasts one to three months. The beetle will be white with a soft exoskeleton. As the outer shell hardens, it will turn brown and then black. The beetle does have hard wings, but it is unable to fly.
After about one to two weeks of adult life, beetles will begin to mate and reproduce. A few days after mating, female beetles will burrow into soil or substrate and lay eggs. Darkling beetles are prolific breeders and females can lay hundreds of eggs during their adult lives.