Finding small insects in pantry staples like cornmeal can be an unwelcome surprise. These pests, generically called “cornmeal bugs,” can infest various dry goods, making accurate identification helpful. This article describes the appearance of these common pantry invaders at different life stages and forms.
Appearance of Adult Cornmeal Bugs
Adult “cornmeal bugs” are small beetles, measuring 2 to 4 millimeters (about 1/8 inch) in length. Their bodies are reddish-brown, though some can be dull orange or dark brown. These beetles have a flattened, elongated, and shiny appearance, which allows them to maneuver into tight spaces.
Their antennae are a distinguishing feature, though difficult to observe without magnification. Antennae shape and segmentation vary between species. Some species have antennae that gradually widen towards the tip, while others have a more abrupt, club-like enlargement. Adults are active and move quickly when disturbed.
Identifying Larval Stages
Larvae, the immature forms of these pantry pests, look different from the adults. They are worm-like and slender. Their color is whitish or yellowish, sometimes with a hint of brown or pale yellow.
Full-grown larvae reach 3 to 6 millimeters (about 1/8 to 1/4 inch) long. Some larvae have a darker, brownish head and small legs. The last segment of their abdomen may end with two small, dark projections.
Common Types of “Cornmeal Bugs”
The term “cornmeal bugs” refers to species like flour beetles and sawtoothed grain beetles. Flour beetles, such as the red flour beetle (Tribolium castaneum) and the confused flour beetle (Tribolium confusum), are reddish-brown and about 3-4 mm long, sharing visual similarities. A key difference is their antennae: the red flour beetle has a three-segmented club, while the confused flour beetle’s antennae gradually enlarge towards the tip. Red flour beetles may fly in warmer temperatures, whereas confused flour beetles do not.
Sawtoothed grain beetles (Oryzaephilus surinamensis) are another common type, distinguished by six saw-like projections on each side of the thorax. They are flat-bodied and brown, measuring 2.5 to 3 mm. Unlike some flour beetles, sawtoothed grain beetles do not fly.
Where These Pests Are Found
These pantry pests are found in various dry food products beyond cornmeal. They infest items such as flour, cereals, pasta, and pet food, and also found in dried fruits, nuts, spices, and chocolate.
They thrive in environments with a consistent supply of milled grains and processed food. Their flattened bodies allow them to squeeze into small cracks and imperfections in food packaging. Infestations often begin with contaminated products brought into the home, or spread from existing hidden sources within the pantry.