Anatomy of Mealworms

The mealworm is not actually a worm at all. Mealworms are darkling beetles, also known as Tenebrio beetles, in the larval stage. In the United States the mealworm is commonly used as food for pets such as birds, reptiles and amphibians. In other parts of the world many people use mealworms as a food source that is low in fat and high in protein.

  1. External Anatomy

    • Because the mealworm is not a true worm, its body is not fleshy but yellow, segmented and rigid. The mealworm's body has 13 segments--a head, three thoracic segments and nine abdominal segments. As in all insects, the mealworm's skeleton is on the outside of its body, giving the soft inner body an armor-like coating of protection. Mealworms shed this outer layer in a process called molting, in which the layer splits open allowing the mealworm to expand before the new armored shell hardens. The mealworm may undergo this process a dozen or more times during the larval stage.

    Head

    • The head of the mealworm looks very similar to the heads of other larval-stage insects, such as the caterpillar. The head has two compound eyes, two antennae and mandibles. The mealworm uses its strong mandibles to chew through its food.

    Thoracic and Abdominal Segments

    • Behind the head of the mealworm are the thoracic and abdominal segments. On each of the three thoracic segments there is a pair of legs. The mealworm pulls itself along by these six short legs. The legs being so short creates the appearance that the larva has no legs at all, thus accounting for the "worm" in its name. The nine abdominal segments end in a spine. While the spine poses no threat to humans or animals, it may be used to help the mealworm to burrow into its habitat.

    Habitat and Food

    • The grain silo is a favorite habitat of the mealworm.

      In the wild, mealworms are found in fields where wild grasses and seeds are plentiful. They can be found under rocks and logs. Mealworms prefer a dry, warm and dark environment Mealworms are found in great numbers in grain silos, barns and food preparation facilities. Because the main food source for the darkling beetle is grain, they have become minor pests in areas where grain is processed. Mealworms also fare well in captivity, and because of this they are used in classrooms all over the world as pets.

    Life Cycle

    • The life cycle of the darkling beetle is very similar to that of the butterfly. The larva will undergo a complete metamorphosis. The female beetle lays hundreds of eggs; when these eggs hatch they become mealworms. The mealworm's primary job is to eat and grow larger and larger. When the mealworm is just under an inch long it enters the pupal stage. Pupae may seem inactive, but they are transforming inwardly into the adult stage. Once in the adult stage, the darkling beetle will first be white and then slowly gain its dark brown color. The adult darkling beetle lives an average of two months, and the entire life cycle of the beetle takes a year to complete.