Anobiid Beetles

Here in western Washington we take for granted that we aren’t plagued by many of the pests found in other parts of the country but that doesn’t mean we are immune. Termites may be rare but other wood pests frequently damage our homes. Ask any realtor about wood boring beetles and you’ll likely see them cringe at their mention.

Insects like wood boring beetles help recycle our forests by returning nutrients to the soil for use by younger trees.
This recycling is good for forests but not so good for homes.

The most common and destructive wood boring beetle in Washington is the California Deathwatch beetle (though it doesn’t inhabit California). Otherwise known as Anobiid beetles and sometimes referred to as powder post beetles (“powderpost” actually refers to a different beetle family) these insects are rarely seen. Their damage on the other hand is found in homes throughout the state and is easily identified.

Anobiid beetles typically infest wood that is high in carbohydrates (sapwood) with an elevated moisture content between 12 and 15 percent.

Female beetles will seek out suitable wood and will even taste it to insure the success of her young.

Carefully inserting her ovipositor (egg laying organ) into the wood grain she injects eggs into the surface. The young hatch and develop, leaving no visible hole as they burrow into the wood consuming it as they go.

As they digest the wood it is reduced to a fine powder of fecal material called “frass”.

When they are ready to mature the larva work their way back to a point just below the wood surface where their skin hardens into a “pupa”. They go through metamorphosis and when conditions are favorable the following spring they emerge as winged adults by chewing a small but visible hole to the surface.

As they exit the wood, frass (digested wood) is frequently expelled from the exit hole and this is often the first sign that you have an infestation. Combined, these exit holes give infested wood the appearance of having been shot with “bird shot”.

Individually, the beetles do little damage but collectively and over the course of several years they can reduce large timbers to dust and ribbons that cannot support a structure.

Some types of construction are more vulnerable to infestation than others.

Homes built without vapor barriers or crawlspace ventilation are extremely vulnerable. But, even modern homes can suffer if we block the foundation vents, add decks, or make modifications that trap moisture in the crawlspace.

The best way to avoid this insect is to keep your home in good repair.

· Dryer ducts, stove exhausts, and bathroom vents should never be directed into the crawlspace or attic.

· Avoid blocking foundation vents especially between the end of February and beginning of November. You won’t save enough on heat to make it worth repairing the sub-floor.

· Leave an airspace along the foundation for ventilation by keeping plants cut back at least 12 inches along the walls 

of your home.

· Make modifications that will help remove moisture from the structure. Make sure a vapor barrier and foundation vents are installed if they were not part of the original construction. Be sure there is no standing water under your home during any season.

· If you have a service person under your home, be sure they don’t move the vapor barrier and expose soil in the crawlspace.

· Do not insulate your crawlspace without having it inspected first. You don’t want to have to pull out the insulation if beetles turn up afterward. (usually about the time you are ready to sell your home). You may also want to consider preventive treatment to avoid the chance of future infestation.

If you do discover beetle damage, it is a sure sign of high moisture. Have the infestation treated professionally, follow the recommendations to control moisture, and keep proof of treatment in a safe place. (this can help you avoid having to treat again if you sell or refinance your home).

Comments are closed.