Yellow mealworm
Tenebrio molitor L.


Secondary pest: fungus feeder and scavenger
Order: Coleoptera
Family: Tenebrionidae
Acronym: TMO


  • Adults are large (12 to 18 mm), dark brown or black shiny beetles
  • Larvae are initially white, but as they mature they turn a characteristic yellow and reach a length of 30 mm at maturity.

Similar species

Commodities affected

  • Prefers decaying grain or milled cereals that are moist and going out of condition
  • Will also feed on products not out of condition: meal, flour, bran, grain, coarse cereals, bread, crackers, mill sweepings, meat scraps, feathers and dead insects
  • Is occasionally found in bags of fertilizer, bales of tobacco, ground black pepper
  • Is occasionally found in dwellings

Signs of infestation

  • Damp and out-of-condition grain with larvae


  • Damage is generalized and not readily identifiable as being caused by this insect pest

How to control

Geographic range

  • Is distributed around the world and across Canada

Where found

  • Prefers damp, old grain that has gone out of condition
  • Is an indication of poor sanitation when present
  • Is most often found in areas that are dark and damp: grain bins, sacks of feed, mills, elevators, feed plants, warehouses and in the litter of domestic fowl houses

Life history

  • Adults appear in early summer.
  • Females deposit eggs singly or in clusters in the food or on the sides of bins.
  • Females lay 300 to 500 eggs.
  • Larvae are resistant to dry and cold conditions and can survive up to 3 weeks at temperatures of -15°C, but prefer 25°C and moist conditions.


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Did you know?

The yellow mealworm is the largest of the insect species that attack stored grain and grain products.