The term “cornmeal bug” is a common, non-scientific name used by homeowners to describe small, reddish-brown beetles found infesting stored dry food products. These pests are technically known as stored product pests. The name most often refers to two species: the Sawtoothed Grain Beetle (Oryzaephilus surinamensis) and the Confused or Red Flour Beetle (Tribolium confusum or Tribolium castaneum). Finding these insects in dry goods signals contamination, making identification the first step toward resolution.
Visual Identification of Pantry Beetles
Both the Sawtoothed Grain Beetle and the Flour Beetles are generally reddish-brown and very small, measuring between 1/10 and 1/8 of an inch (2 to 3.5 millimeters) in their adult stage. Distinguishing between them requires a close look at the shape of the body just behind the head, known as the thorax. The Sawtoothed Grain Beetle is notably slender and flat, a characteristic that allows it to easily slip into tiny crevices and packaging seams. Its defining feature is a series of six distinct, saw-like projections or “teeth” lining each side of the thorax, giving the insect its name.
Flour Beetles, including both the Confused and the Red species, are more oval and less flattened than their sawtoothed counterparts. These beetles lack the distinctive projections along their thorax, which appears smooth and more rounded. The larvae of these pests also appear different and are often found directly in the infested product, looking like tiny, whitish-yellow worms.
Sawtoothed Grain Beetle larvae are slender, creamy-white grubs that grow to about 1/8 of an inch long, possessing a brown head and three pairs of legs near the front. Flour Beetle larvae, which can grow slightly larger, are also yellowish-white but feature a distinguishing pair of dark brown, hook-like appendages at the tip of the abdomen.
How Infestations Begin
Pantry beetle infestations almost always start with the purchase of an already contaminated product from the store, such as flour, cereal, dry pet food, or spices. The adult beetles, or often their eggs, are present in the packaged goods when they are brought into the home. These pests are considered secondary feeders, meaning they prefer milled products, cracked kernels, or damaged grains.
Their small, flat body structure allows them to exploit tiny defects, crawling through thin cracks, packaging folds, and even pin-sized holes. Though they are not strong chewers, they can also bore through thin packaging materials like paper, thin cardboard, and cellophane to access new food sources. Once inside a pantry, the beetles reproduce continuously, completing their life cycle in as little as 30 to 40 days under warm, undisturbed conditions.
The beetles spread easily from one item to another, contaminating multiple packages as they wander across shelves. Any spilled food particles or dust left in the corners of a cabinet can serve as a breeding ground, allowing the infestation to persist and spread.
Prompt Removal and Cleanup
Upon discovering cornmeal bugs, the immediate disposal of all infested or suspected items is necessary. All contaminated dry goods must be sealed tightly in a plastic bag and promptly removed to an outdoor trash receptacle to prevent the beetles from returning. Any items that were stored nearby should be inspected closely.
For items that cannot be discarded but may be contaminated, temperature treatment is an effective method for killing all life stages, including eggs and larvae. You can place the sealed items in a freezer at 0°F (-18°C) or lower for a minimum of four days to ensure complete mortality. Alternatively, for items like whole grains, you can heat them in a shallow pan in an oven at 140°F (60°C) for 30 minutes.
After disposal, the entire storage area must be thoroughly cleaned. Vacuum all cracks, crevices, and shelf supports to remove stray debris, eggs, and larvae. The shelves should then be wiped down using hot, soapy water to eliminate any remaining food traces that could sustain a new infestation. Avoid using household pesticides on food-contact surfaces, as this can lead to chemical contamination.