Facts About Meal Worms

The larvae stage of the darkling beetle (Tenebrio molitor), known as the mealworm, lives under rocks and logs where the soil is cool. The worms consume leftover debris from insects, small mammals and plant life. The mealworm grub, a favorite diet for lizards, birds and spiders, prefers living in complete darkness where they feel safe from predators. They play an important role in the ecosystem by providing valuable food and cleaning up unwanted debris.

  1. Eggs

    • Hundreds of eggs laid by the darkling female beetle hold tiny mealworms. Each oval, white egg takes between four and 19 days to hatch. Each mealworm measures 1/2 to 3/4 of an inch long. They appear white with a dark head.

    Stages

    • During the mealworm's life it will molt its exoskeleton nine to 20 times as it grows. The mealworm has a voracious appetite and molting allows the worm to grow rapidly. During its heavy feeding, it eats many beneficial things for the environment but it also enjoys seedlings and young plants, which makes the mealworm a nuisance to many gardeners. This stage lasts from three to five months before it molts into the pupa stage.

    Pupa

    • The pupa is creamy white with a large head. During the pupa stage the insect consumes no food and rarely moves. The insect puts all of its energy into changing into an adult beetle. The stage of a pupa varies. In the summer, it can last from two to three weeks before the adult darkling beetle emerges. In the winter, the transformation may be delayed for up to nine months.

    Adult Darkling Beetle

    • The adult darkling beetle breaks out of the pupa skin. It emerges a beetle with a hard outer shell. The beetle has six legs and two antennas protruding from its head. An adult beetle's diet does not differ from the mealworm stage. It continues to eat the same diet but not in the same abundance.

    Defense Mechanism

    • As an adult, the insect offers a defensive posture when disturbed by standing on its head and pointing its rear end at the intruder to excrete an unpleasant odor. The gaseous odor also turns the intruder's skin brown.

    Pet Stores

    • Most pet stores sell mealworms to feed to aquatic life, reptiles and small mammals. Large mealworms marketed at pet stores tend to be treated with hormones to prevent them from advancing to the pupa stage and beyond. Smaller mealworms have not been treated and will continue to grow and change into adults.