What are Wood Boring Beetles?

Present on all continents but Antarctica, wood-destroying Beetles (coleopteran order) are part of our ecosystem and help decompose dead and dying trees into rich organic material. Depending on their specie, wood-boring beetles can infest wood from healthy and green to dried lumber, seasoned wood and even older antique furniture. Some beetles live for years causing damage to appearance and structural integrity of infested wood.

The most common species in Marin County are the Lyctid (true powder post), the Bostrichic (false powder post), the Anobiid (deathwatch or furniture) and the Cerambycid (old house borer). A few other species like the Buprestid (flat head or metallic), the oedermerid (wharf borer) and the scolytid (bark borer) are also found outside and sometimes in exterior siding. Seldom seen by humans, the beetle’s most visible sign of infestation are emergence holes on the surface of infested wood members and powder beneath.

True Powder Post Beetles (Lyctid)

The Lyctus beetle is the only “True Powder Post” beetle and produces a very fine talcum-like powder when emerging through small round exit holes. Indigenous and most common in California, it favors seasoned hardwood (oak, ash, mahogany, etc.) and can be seen in hardwood floors as well as furniture. Sometimes Lyctus beetles emerge from new furniture made with previously infested wood containing dormant eggs. It can re-infest the same untreated wood to produce new generations and eggs will hatch with warmer conditions ideal for survival and reproduction. Re-infestation is unlikely in varnished and treated wood.

False Power Post Beetles

Often referring to several wood-destroying species such as Anobiid, Bostrichid and Cerambycid, they are found worldwide in structural wood members and furniture. Emergence holes are often seen on the surface of wood members, door and window frames and antique furniture. Eggs survive for years and hatch when the environmental conditions (temperature and humidity) are conducive to their survival and reproduction.

Polycaon Stoutii (Bostrichid)

Commonly known as the “Black Polycaon”, it is one of the largest wood-boring California beetles. Easily spotted by humans it rarely re-infests wood and favors hardwood over softwood. Sometime infesting structural wood members of homes in fairly humid areas, it emerges through large round holes to mate and reproduce.

Treatment and Prevention

For larger infestations, fumigation of the entire structure is the only way to ascertain complete eradication of wood-boring beetles. Since fumigation have no residual effect, it will not prevent re-infestation if local conditions (humidity and temperature) are favorable to local species. All beetles favor fairly moist wood (17% to 30% humidity) and the best is to eliminate or limit humidity as feasible with proper drainage in and around the structure and dryer basements and crawl spaces, and vapor membranes covering substructure soils. 

In a dryer environment, or once the excessive moisture condition has been addressed in basements and crawlspaces, a surface treatment with a borate based material such as TimBor or BoraCare (dosidium octaborate tetrahydrate) will deter further re-infestation of wood boring beetles. We also recommend periodic applications of wood preservatives or coatings (paint or vanishes) on exterior wood members to deck, stairs or balconies to deter further re-infestation.