The yellow mealworm (Tenebrio molitor) is the most common species of mealworm bred around the world. It is not a worm, it is a larvae stage (immature stage between egg and pupa) of the Darkling Beetle. 

Lifecycle

The lifecycle of the mealworm comprises of the following 4 distinct stages. Click Here for more details:

  1. Egg
  2. Larva (worm)
  3. Pupa
  4. Beetle
mealworm

Photo of the Mealworm Lifecycle (photo by uen.org)

Behavior

Mealworms (beetle and larvae) are active both day and night, however they are more active in darkness.

They avoid light and burrow when left exposed. They do not fly, and are not able to climb smooth surfaces such as smooth plastic or metal.

photo of mealworm pupa and beetles in a blue mealworm tray. Beetles have climbed onto square egg carton

Natural Habitat 

In the wild mealworms eat grains, organic material such as plants and decomposing animal material. They live in leaf litter or areas with good cover. They are found in close association with bird droppings or left over foods. Many outdoor bird aviaries will have other species of mealworms that eat left over seed, and scraps.

Its this capacity to eat a wide range of foods and in particular grains, flour, pellets, pet foods and other agricultural products.

Photo of moth egg debris coming from a large white bag of mealworm bran. Egg debris is coming out of the bag seal at the top.

Human Uses

Mealworms are used as food for pets, zoos, and wildlife rescue. They are also used as food either directly or indirectly by feeding them to chickens, fish or pigs.

Distribution

Mealworms inhabit temperate areas and most likely originated from the Mediterranean region. Their natural range also extends to North Europe and the UK. They have spread across many parts of the world with trade and are a pest in grain stores in many areas.

photo of a group of yellow mealworms close up on a white background

Food and Water

In the wild mealworms eat grains, organic material such as plants, grains, some seedlings and decomposing animal material. They live in leaf litter, compost or areas with good cover. They are found in close association with bird droppings or left over foods. Many outdoor bird aviaries will have other species of mealworms that eat left over seed, and scraps.

In captivity they eat grain based substrates such as wheat (bran, mill run, pollard) or oats. They can be fed pellets for chicken or other omnivore food. They do not drink free water, and get their moisture from wet foods such as vegetables and fruits. The larvae can go without wet foods for long periods and sustain themselves by obtaining moisture from humid air.

Photo of thin pieces of carrot being eaten by yellow mealworms. Thousands are devouring the carrot from all sides.

Anatomy

Beetle shares the same characteristics of most insects having: head, thorax, antennae, wing shields and six legs. Beetles emerge  from the pupa white, then go light brown and finally black.

Larvae (worms) has six pairs of legs near the head of the worm which are difficult to distinguish. The worms have numerous instars (shed between growth spurts) and white after they molt.

Classification

Kingdom Animalia (animals), Phylum Arthropoda (arthropods), Class Insecta (insects), Order Coleoptera (beetles), Family Tenebrionidae, Genus Tenebrio, Species T. molitor.