Insect Factsheet

Yellow Mealworm Beetle/Darkling Beetle (Tenebrio molitor)

Identification: Adult beetles, approximately 28mm in length and shiny, dark-brown or black, resembling many ground beetles in shape, size and colour.

The mealworm themselves are the larval form.

Larvae up to 20mm in length are a honey-yellow colour with hard, highly polished worm-like body.

Yellow Mealworm Beetles are considered scavengers and are among the largest insects that infest stored products. Most prefer to feed on decaying grain or milled cereals in damp, poor conditions.

Indoors, they are usually found in basements or at ground level, sometimes infesting cornmeal, flour, cake mixes, cereals, meat scraps, dead insects, bran and litter from chicken houses, they have even been found in sparrow's nests where they feed on the droppings. Mealworms have been found living under old carpeting and in straw-stuffed chairs in damp areas.

Yellow mealworm larvae make excellent fish bait and serve as food for animals in aquariums and zoological parks as well as wild bird food.

Female beetles' can lay up to 500 eggs over a period of 3 – 5 weeks, larvae emerge after 2 weeks and feed on any available foodstuffs.

Individual larvae may wander far from the food source to pupate, making it difficult for homeowners to locate the source of infestation.

They are a slow breeding pest; the adult beetles evolve over 1-2 years. They can reach a size of 28mm in length. Because of the beetle's long development period an infestation is often due to poor hygiene or the remains of old food.

Control: If lots of beetles are found in a domestic environment check in and under kitchen units for spilled or old food or infested bags of flour etc.

Check in lofts and roof spaces for old birds’ nests.

Clean up thoroughly and throw away any old or infested stocks of food.

The area should then be thoroughly cleaned, and a residual insecticide labelled for ‘crawling insects’ can be used.

Use an insecticide spray sold for 'crawling insects' that is labelled as safe for use in kitchen areas. After you have treated, be aware that further mealworms may hatch so you may need to keep treating until all the eggs have hatched out and infestation has completely gone.

Use biocides safely. Always read the label and product information before use.