Dark mealworm
Tenebrio obscurus F.


Secondary pest: Grain feeder
Order: Coleoptera
Family: Tenebrionidae
Acronym: TOB


  • Adults are similar in appearance to the yellow mealworm, but are often lighter brown in colour.
  • Adults are long (12 to 18 mm).
  • Dark mealworms may be distinguished from the yellow mealworm by the presence of more dense punctures on the head and pronotum than are present on the yellow mealworm.
  • Larvae are cylindrical and move readily through the commodity.
  • Larvae are initially white, but darken as they mature and reach a length of 25 to 30 mm.

Similar insects

Commodities affected

  • Prefers to feed on grain and milled products that are damp and decaying and have been left undisturbed for some time
  • Will also feed on sound food items such as meal, flour, bran, grain, coarse cereals, crackers, meat scraps, feathers, dead insects

Signs of infestation

  • Larvae and adults are large and readily visible.
  • Odours from out-of-condition grain are often noticed before presence of insects, but insects also produce disagreeable odours.


  • Damage is generalized and not recognizable as being caused by this species

How to control

Geographic range

  • Is found worldwide and across Canada

Where found

  • Is usually found in association with damp, moldy grain
  • Is most often found in dark and damp places, grain bins, sacks of feed, litter of chicken coops and birdhouses, stables, mills, elevators, warehouses, feed mills
  • Is often found in association with the yellow mealworm (Tenebrio molitor)

Life history

  • Adult females lay 400 to 500 eggs.
  • Dark mealworms will readily feed on other insects.


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Did you know?

The dark mealworm is often found along with the yellow mealworm (Tenebrio molitor) infestations.