Foreign Grain Beetles in New Homes Back »

Written collaboratively by Amanda Bachmann, Patrick Wagner, Adam Varenhorst, and Philip Rozeboom.

One of our most frequently asked insect questions this year was about the foreign grain beetle. These small, reddish-brown beetles seem to appear out of nowhere inside homes. Their name implies that they are a pest of grain, but they actually feed on the mold and fungi associated with stored grain. Interestingly enough, the foreign grain beetle samples we receive most frequently come from newly constructed homes rather than grain bins.

Foreign grain beetles look very similar to some of the other common stored grain pests. They are similar in shape (elongate) and color (reddish-brown) to some of the common grain pests, but they are about half the size (barely 1/8 inch long) of these other beetles. Unfortunately, their most distinguishing characteristic (knobs on the front corners of their thorax) is only visible under magnification (Figure 1).

Elongate, reddish-brown beetle on a white background.
Figure 1. Foreign grain beetle. Note the knobs on the thorax (the segment behind the head). Courtesy: Amanda Bachmann

The good news is that these beetle populations tend to disappear on their own. The adults that emerge from wall voids and other spaces inside new construction are generally unsuccessful at beginning another generation indoors. They can be managed like many of our other fall invaders by vacuuming or sweeping up the adults and disposing of them and no insecticide application is necessary.

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