Jeff Hahn
Entomology Educator
John F. Kyhl
Entomology Technician
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FOREIGN GRAIN BEETLES
Jeff Hahn
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Foreign grain beetle (Actual size: 1/12 inch) |
peg-like structures |
Foreign grain beetles, Ahasverus advena, are common in August and September as temperatures cool and humidity and rainfall increase. Foreign grain beetles are about one twelfth (1/12) of an inch long and reddish-brown in color. When viewed under magnification, foreign grain beetles can be identified by the two peg- like projections behind the head (see figure). These small beetles are strong fliers, and are sometimes confused with fruit flies or gnats. However, foreign grain beetles are harder shelled than flies and lack conspicuous, clear wings. Sometimes people are concerned these beetles are fleas or lice but neither of those insects can fly.
Foreign grain beetles normally exist outside as scavengers, feeding on plant and animal debris and their associated fungi. They frequently enter homes, and once indoors are often seen around sinks, bathtubs, and other sources of moisture, such as plumbing leaks and condensation from pipes. Fortunately, foreign grain beetles do not bite and are harmless to people. They do not destroy furniture, clothing or other property. Foreign grain beetles prefer grain that is old and moldy and are rarely found in dry food products in the home.
Most complaints about foreign grain beetles come from people living in new homes. Beetles infesting new houses are sometimes found in wall voids feeding on the fungi that grow on moist wood and drywall. If populations are high, they can be seen exiting around baseboards, wall sockets, and ceiling fixtures. The molds in new homes normally die within one to three years as the wood dries. As the fungi disappear, so do the foreign grain beetles.
Control the beetles found in a house with a vacuum cleaner or remove them by hand. Insecticides are rarely warranted because foreign grain beetles do not reproduce outside of the walls and have short lives. Although infestations of food products are rare, check susceptible food (like flour, dried fruits and beans) to be on the safe side. If necessary, store products in insect-proof containers to prevent problems.
Foreign grain beetles occasionally enter buildings from the outside. The small size and high mobility of foreign grain beetles makes it difficult to keep them out of homes. They can easily enter through window screens and seals around doors and windows. You can try to prevent their entry by caulking or sealing obvious entry points, but foreign grain beetles will probably still get inside. An application of insecticide by a pest control operator of a long-lasting insecticide, such as Tempo or Demon, to the outside of a structure may provide control if beetles are entering the house in large numbers. The indoor use of insecticides to control invading foreign grain beetles is not recommended.
Foreign grain beetle numbers drop dramatically by October. Once the humidity falls below 60%, foreign grain beetles die and disappear on their own.
E603F
Revised 11/98
