Mealworms are the larvae of the darkling beetle or tenebrio beetle. They are about 1/2 to 3/4 inches in length when they are young and grow up to 1 1/4 inches long when they are full-grown. They are light golden in color, darkening as they grow older. They stay larvae from 90 to 114 days and eventually transform into a pupa, continuing the metamorphose process. They are often used as a food source for reptiles, birds, fish and small mammals.
The survival of mealworms is largely dependent on an accessible food source, providing them energy to continue the metamorphosis process. Their dietary choices are broad, making them able to survive in a number of different environments. The mealworm larvae eat grasses, decaying leaves, dead insects, stored grains and feces. Any of these food sources alone or in conjunction with another provide a habitat more than suitable for mealworm survival. Mealworms consume lots of food at this stage of their development, so to continue growing they need a steady supply of food.
The habitat of a mealworm is more dependent on their access to food, rather than a particular preference. In the wild, they are found under rocks, logs, animal burrows and anywhere with an active food source. They also enjoy grain storage areas and hard to keep out. Acting as natural caretakers, mealworms make their home anywhere excess biological waste occurs. They are not aquatic in nature, preferring dark areas that are moist with cover. The excess waste produced by humans has made mealworms increasingly dependent on urban areas and less common in the wild.
Mealworms will survive a number of different temperatures, making them resilient insects. They prefer to survive in temperate climates, but are capable of living in areas with temperatures as low as 4 degrees Celsius. Since, they are not readily used as food for a variety of different species of animals and birds, they are often kept in refrigerators to maintain their freshness. The only real effect this has on them is that it slows down the process of metamorphism that they go through. They will withstand the conditions of a refrigerator for a couple of weeks before they need to be removed.