Wood Boring Beetles

Wood Boring Beetles

Beetles found in the United States may vary in size by species from about 1/25th of an inch, or about one millimeter, up to about three inches in length for the largest beetle species. There are a number of wood boring beetles encountered in structures. The beetles that attack and damage structural lumber are relatively small beetles. These beetles are from about 1/8th of an inch up to about an inch in length depending upon the species.

The characteristic damage caused by beetles varies by species. This damage may be used to identify the problematic species infesting the structure. The most significant damage is caused by the developing larvae within the wood. Once the larval development has been completed, the new adult beetle chews an exit hole from the wood surface.  Such exit holes are a telltale sign of wood boring beetle infestation and damage. See photo.

The powderpost beetles are the most significant threat and responsible for the most beetle caused damage to structures in the United States. They are called powderpost due to the characteristic damage they cause. Damaged wood contains powder like frass created by the developing beetle larvae during their feeding upon the wood.  These beetle larvae excavate galleries in the wood which are packed with their frass or powder like substance.

Since full development of these beetles may take from months to years, depending upon various conditions, significant damage may take many years to occur and require generation after generation of beetles. The term powderpost beetle is a general term and includes a number of species. Powderpost beetles may include beetles entomologically classified in the families Anobiidae, Lyctidae and Bostrichidae. These beetles are small and often not seen. See photo.

The life cycle of these beetles is considered complete metamorphosis which includes egg, larvae, pupae and adult. The adult female deposits eggs on suitable wood. Eggs may be deposited on the surface, in existing exit holes, cracks, crevices or other surface imperfections which may be present. After hatching, the larvae tunnels into the wood where it will spend from months to years in the development process. The fully developed larvae may tunnel nearer the surface where they form a pupal case. Once the fully developed adult beetle emerges from the pupal case it then tunnels through the surface creating a visible exit hole. The size of the exit hole varies with the beetle species which created it.

Other Wood Boring Beetles
There are a number of wood boring beetles which may be found active within a structure. The species or type of beetle found may vary by region of the country. Examples of some beetles which may be active in structures include but are not limited to the old house borer, the wharf borer, the sawyer beetle, the flat oak borer, the golden buprestid, the ambrosia beetle, bark beetles and ambrosia beetles. While it is possible that these beetles may cause structural damage, the incidence of structurally significant damage is less than that of powderpost beetles.

Telltale Signs of Wood Boring Beetle Activity and Damage
Wood boring beetle activity and damage may be detected during a visual inspection provided that the inspector knows what to look for, where to look and how to look.  The telltale signs of wood boring beetle activity include exit holes, frass, damaged wood, beetle carcasses and live beetles.

As mentioned previously, exit holes are created when the fully developed adult chews its way out from inside the wood. These exit holes are apparent on wood surfaces are an indication of wood boring beetle activity and possible damage. Depending upon the beetle species present, exit holes may vary in size from about 1/50th of an inch, for small ambrosia beetles, up to about ½ an inch for flat headed borers. Holes may also vary in shape with species from round to oval. The number of exit holes may be indicative of the degree and duration of infestation and related damage.

Frass is the fecal matter and remnants of chewed wood excavated by the wood boring beetle. Frass may present in various consistency from fine, talc like powder to more coarse material.  It is common to find accumulations of such frass on various horizontal surfaces under wood boring beetle exit holes. Significant accumulations of frass may be found atop poly sheeting surfaces within crawl spaces of structures which have been infested an extended period of time. Such frass may simply fall from exit holes or pushed out as a result of pest activity. The presence of frass alone may not indicate an active infestation.

Over time the feeding activity of the developing larvae causes damage to the wood being fed upon. Given sufficient time, significant damage may occur requiring costly structural repairs. Damaged wood may be detected during inspection. Indications of damage may be detected visually, as in the presence of numerous exit holes, or through the use of inspection techniques such as probing and sounding of structural wood. Inspection techniques are discussed later.

Beetle carcasses and live emerged adult beetles may be present and observed by an experienced and competent pest professional conducting a thorough WDO inspection. Adult beetles emerge from the infested wood and may be attracted or drawn to light sources. These beetles may be found along windows, lighting and other such areas. Powderpost beetles are small insects which may be difficult to find and recognize when present.

The Importance of Annual Inspections
Whether we’re dealing termites or other WDOs it is prudent to inspect the structure at least once per year. In fact, pest management industry and entomological references recommend inspections should be done on at least an annual basis. This is especially so in those areas of the country where the risk of WDOs, such as subterranean termites, may be common. Such inspections are conducted in order to detect the presence of WDO activity before significant damage occurs as well as those conditions present which may require correction. As such, the annual inspection is an important part of any WDO prevention and management program.

Visual Inspections
In the recent past there seems to have been much discussion within the pest management professional industry regarding the conduction and limitations of visual inspections. Such inspections are usually conducted due to real estate transactions are intended to report the presence or absence of WDO activity at a structure at the time of the inspection. Industry jargon may refer to this as a snapshot in time.

Of course, the snapshot in time references what was observed at the time the inspection was conducted which is understandable. What is often called into question is: what exactly is a visual inspection of a structure, what’s included and what is excluded?

Powderpost Beetle Damage