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Insects and other arthropods

Yellow mealworms

Tenebrio molitor

Tabs group


Adult yellow mealworms are shiny, sturdy, dark brown to black beetles and measure around 16 mm (14–18 mm) in length. They are the biggest insect pests to infest whole and ground grains. Males are usually smaller and slimmer than females.

Life cycle

Adults living in the wild appear in early summer and mate right away. Females lay on average 400 to 500 eggs, which are deposited singly or in small clusters. The shiny white eggs hatch after 4 to 18 days. The larvae, about 2 mm long, are white, but take on a golden yellow tinge as they grow. In an unheated area, the larval stage can last from six to nine months, and sometimes even up to one year. The insect remains in the larval stage through the winter.

The larvae undergo 10 to 16 moults during their development and reach an average length of 30 mm before they change into pupae. Their white colouring turns gradually to yellow during pupation. Mealworms remain in the pupal stage for two to three weeks before emerging as winged adults. These die within two to three months. Depending on conditions, the complete life cycle of yellow mealworm beetles can last anywhere from four months to two years.

Geographic distribution

Yellow mealworms are found everywhere in their habitat in Quebec, across Canada and the northern United States. Thought to have originated in Europe, they now occur worldwide.

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