Mealworms are the larvae of darkling beetles. They are often raised as food for pet lizards, fish and birds or used by fishermen as bait. Adult darkling beetles lay their eggs in soil, and the eggs hatch after a period of time ranging from a few days to one month. Mealworms begin to eat as soon as they hatch.
Mealworms molt their hard exoskeleton several times as they grow. A freshly molted mealworm has pale skin that darkens to a tan or brown color as it hardens. Mealworms thrive in dark, warm environments with abundant food. They eat voraciously and enjoy nearly every type of plant-based food. In the wild, mealworms eat seeds, decaying plants and fungi. In captivity, they enjoy oatmeal, cornmeal or other crushed grains, dog food, cat food, birdseed, fruits and vegetables.
Mealworms prefer a vegetarian diet, but in overcrowded conditions, they have been known to eat each other. When a mealworm has eaten enough, it forms a hard shell around itself and moves to the next stage of its life cycle, the pupa. Pupae do not eat or move for two to three weeks. After this time, the shell splits open and the darkling beetle emerges.