Skip to main content

Don't worry about foreign grain beetles

Foreign grain beetles, Ahasverus advena, have been very common in homes during September. They are very small, about 1/12 inch long, and reddish brown. Under high magnification, you can distinguish this beetle from others by a pair of peg-like projections behind their head. In homes, they are commonly found around sources of moisture, such as sinks, basins, and bathtubs.
Tiny foreign grain beetles have been common in
homes lately.  Photo: Jeff Hahn, UMN Extension.

These insects have been confused as possible bed bugs, https://extension.umn.edu/biting-insects-and-insect-relatives/bed-bugs. Because of the increase in bed bug problems, people have been sensitive to small insects they can not identify. Once these insects are examined closely, they difference between can be readily seen.

Note: If there is ever any doubt as to the identification of an insect, especially if bed bugs are a concern, have it examined by an expert.

Foreign grain beetle are scavengers, feeding on fungi, mold and organic material. Despite their name, homeowners rarely see foreign grain beetles attacking their stored food products, such as flour or pasta, unless it is old and moldy.

Interestingly, foreign grain beetles are often associated with newly constructed buildings. Moisture from the green wood supports mold and fungus on wood and drywall. Foreign grain beetles feed on this, allowing their numbers to build up in wall voids. Eventually, they come out into the living areas of homes. Foreign grain beetles can also be found in older homes with high humidity and poor ventilation.

Don't confuse foreign grain beetles with bed
bugs.  Photo: Jeff Hahn, UMN Extension.
Fortunately, these beetles are harmless; they do not bite people (even though some people believe they do), damage wood or infest sound food. They are only annoying when they are present.

The best control is to physically remove them, like with a vacuum cleaner, or just ignore them. Insecticides are not necessary because the problem is temporary and the insects are harmless.

Foreign grain beetles are seasonal and will only be around until late September or early October and then they go away on their own. When they are infesting new homes, they persist only for one or two years until the wood dries and can no longer sustain them.

For more information, see Foreign grain beetles.

Author:  Jeffrey Hahn, Extension Entomologist



Print Friendly and PDF