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Foreign Grain Beetles Feed on Mold, Not Grain

By Chris Williams on March 1, 2016.

A couple of months ago our home was overrun with tiny little beetles that were identified as foreign grain beetles. We went through all of the foods in our kitchen looking for the source of the infestation. We never did find it but the beetles are almost all gone now. Do you think they will be back when the weather warms up again?

L. L., Loudon, NH

The expert who identified your beetles should have explained that these beetles are more often associated with mold than with stored grains. Actually the ideal situation for foreign grain beetles is old, moldy grain where they feed on the surface mold rather than on the grain itself. In homes, though, we see them more often in association with damp building materials (see The Foreign Grain Beetle is Actually a Mold Pest) and we consider them to be one of a group of fungus beetles that invade damp buildings.

Foreign Grain Beetles Can Be Pests of New Construction

If you are living in a new home or if you have gone through recent renovations, that could explain the presence of the beetles. Foreign grain beetles frequently build up to high levels in new buildings where wood is still green, and plaster, drywall, and wallpaper are still damp. The beetles feed on microscopic molds that grow on these building materials. Hidden roof or plumbing leaks are another common infestation site.

Whether the foreign grain beetles were feeding on moldy foods or on moldy building materials, in either case it indicates that you have a moisture problem (see Fungus Beetles Mean Things Are Too Damp). When the beetles are infesting building materials, you usually don’t even realize they are there…at first, until numbers build up and the beetles emerge from wall voids and fly to lights.

Hot, Humid Weather May Mean a Return of Fungus Beetles

The key to getting rid of the beetles is to dry out the sites where they are found, lowering the humidity and killing the surface mold. This could mean using dehumidifiers, fans, or heaters to reduce moisture. The drier winter weather and use of home heating may have contributed to the decline of the beetles. They are always at higher levels when outside weather is hot and humid (see Summer Weather Can Bring Pests That Feed on Mold). They may or may not return in the spring, depending on what they were infesting. If you do see beetles again, contact an exterminator for a professional inspection and treatment.

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