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Mealworm Beetle Larva - WWC Archives

The Yellow Mealworm Beetle (Tenebrio molitor), is a species of darkling beetle. Like all holometabolic insects, they go through four life-stages: egg, larva, pupa, and adult. Larvae typically measure about 2.5 cm or more, whereas adults are generally between 1.25 and 1.8 cm in length.


Mealworms are typically used as a food source for reptile, fish, and avian pets. They are also provided to wild birds in bird feeders, particularly during the nesting season when birds are raising their young and appreciate a ready food supply. Mealworms are high in protein, which makes them especially useful as a food source. They are also commonly used for fishing bait.

They can be purchased at most pet stores and bait shops. They are also available via mail order and via internet suppliers (by the thousand). Mealworms are typically sold in a container with bran or oatmeal for food.

When rearing mealworms, commercial growers incorporate a juvenile hormone into the feeding process to keep the mealworm in the larval stage and achieve an abnormal length of 2 cm or greater.

Tenebrio molitor is also used for biological research. Its relatively large size, ease of rearing and handling, and status as a non-model organism make it attractive for proof-of-principle study. Researchers worldwide, but particularly in Sheffield (UK) and Pusan (Korea), currently use this beetle as a model system for studies in biology, biochemistry, evolution, immunology and physiology.


Mealworm beetles (darkling beetles) are prolific breeders. Mating is a three step process:

  1. The male gives chase until the female relents.
  2. The male then mounts the female and curls his genitals (aedeagus) underneath himself and inserts it into her genital tract.
  3. The male then injects a packet of semen into the female.

Dependent on incubation temperature, just days after mating the female will burrow into soft ground and lay about 500 eggs.


After 4-19 days the eggs will begin to hatch. These tiny mealworm eggs make wonderful food for their predators such as reptiles.

Larva stage[]

During the larva stage, mealworms will undergo repeated molting between bouts of eating various vegetation or dead insects. This takes place 9-20 times (instars) as it gets too big for its current exoskeleton. During its last molt, it loses its carapace before curling into its pupal form.

Pupa stage[]

The mealworm remains in its pupal stage from 3 days to around 30 days (dependent on incubation temperature and overwintering). The pupa starts off a creamy white color and changes slowly to brown during its pupation stage.