Foreign Grain Beetles


The foreign grain beetle, Ahasverus advena (Waltl), thrives in humid environments. Scientists have found that it does not reproduce when the humidity is less than 65%.

Appearance / Identification

grain beetle top view
click to enlarge

The foreign grain beetle is a small insect. Adults are usually less than 1/8″ long.

They are slender and flat-bodied. The shield behind the head has distinctive projections on the front corners.

Many people confuse the foreign grain beetle with the sawtooth or merchant grain beetles. These other species are not usually associated with damp conditions like the foreign grain beetle.


What Food Do They Eat?
Scientists classify foreign grain beetles as “secondary feeders”. They normally feed on moldy materials.

The adult beetles deposit their eggs in small clusters. When they hatch, the larvae eat mold, moldy grain, dead insects, and other debris.


What Attracts Them?
Foreign grain beetles invade homes when there are damp, humid conditions.

Where Do They Live?
They have been found in bathrooms where there were plumbing leaks that caused mildew to grow. They have invaded damp basements and crawl spaces where the dampness enabled mold to develop.


How Do You Get Rid of Them?
Eliminating moisture will usually be the critical step in controlling foreign grain beetles.

In kitchens or bathrooms, check for plumbing leaks. The tub trap is a common area where dampness can be a problem.

Crawl Spaces
If crawl spaces are damp, check to be sure the vents are open and are not blocked by shrubbery. Additional vents are sometimes necessary.

In basements, a dehumidifier can sometimes help reduce dampness. Check outside for any moisture sources. Be sure gutters are clean and working properly. Downspouts should drain away from the foundation.

Insecticide applications may be necessary to get complete control. Dust can be injected into wall voids and bath traps. Contact insecticide can be used to eliminate the active adult beetles.

A pest control professional can make the appropriate applications. He or she can also help find the source of the infestation and provide specific advice for eliminating moisture.