Flour Beetle

General Facts

The confused flour beetle, Tribolium confusum Jacquelin du Val, is a common insect that attacks stored grains and foods in the pantry. This insect has a world wide distribution and is very abundant in the United States. It generally feeds on finely ground or broken starch materials, such as flour or meal. Adults and larvae feed on broken kernels and fine-grind materials in granaries, mills, warehouses, and other places where grain or grain products are stored. A closely related species, the red flour beetle, Tribolium castaneum (Herbst), is often found associated with the confused flour beetle. These two species are difficult to distinguish, particularly in the larval stage of development.

The most common Flour Beetle in the northern states is the Confused Flour Beetle. This beetle is about 1/8 to 1/4 inch in length, with a reddish-brown color, and its small size allows it to work its way inside many sealed containers. It will primarily eat milled grain products, such as flour and cereals. Both adults and larvae feed on grain dust and broken kernels, but not the undamaged whole grain kernels. In addition to flour, they will eat rice, dried fruit, nuts, and beans. This beetle will also hide in crevices, and corners of pantries.

They typically spoil foods with fecal pellets, dead bodies, and secretions. Flour Beetles often hitchhike into the home in infested flour and can multiply into large populations. Some survive on food accumulations in cabinet cracks, crevices, and furniture. Confused flour beetles are the most abundant and injurious insect pest of flour mills in the United States. Badly infested flour is characterized by a sharp odor and moldy flavor. They do not bite or sting humans or pets, or feed on or damage the house or furniture. However beetles may be attracted to and eat rat fecal pellets and may contract and can carry tapeworms.



The confused and red flour beetles cannot feed on whole undamaged grain; they are, however, often found among dust, fines, and dockage. The beetles do cause damage by feeding but probably cause more problems by contaminating the grain. Large numbers of dead bodies, cast skins, and fecal pellets, as well as liquids (quinones), can produce extremely pungent odors in grain. The nauseous smell and taste caused by infestations of confused and red flour beetles can result in poor feed consumption by livestock and rejection by grain buyers. In most cases, the presence of live insects in a grain bin indicates that moisture buildup and molds are also present. The combination of these three factors can greatly reduce the quality and value of grain.



Prevention is the best strategy to avoid insect problems in stored grains. Proper bin sanitation before introduction of new grain minimizes the need for pesticides. Good sanitation involves the removal of old grain and dust in and around the grain bin. This includes removal of old grain from corners, floors, and walls. Any grain remaining when a bin is emptied can harbor insect infestations which will move into the new grain. Grain that is to be stored for longer than six months may need a protective application of an approved insecticide.

Before grain is placed in a bin, it should be screened to eliminate fine materials and broken kernels. Grain placed in a clean bin should be checked at two week intervals during warm months and at one month intervals during cooler months for the presence of hotspots, moldy areas, and live insects. If any of these conditions exist, the grain should be aerated to lower the moisture level and temperature.

Fumigation should only be used as a last resort. Because of the high toxicity of registered fumigants and technical knowledge needed for their proper use, a qualified pesticide applicator should be contacted if fumigation is required.