QUESTION:

I was recently called to inspect a medical office for black beetles. I ID'd the beetles as Polycaon stoutii. They are frequently found in various parts of the building on walls, ceilings, etc. I did inspect the very old Oak furniture and could not find any bore holes. Upon checking the attic I did find one attempting to exit through a vent screen. On the exterior there are some areas of overlapping eaves that would allow penetration of fliers to get in as well as some roof vents not properly sealed. There are also about 10 large, mature Redwood/Cedar trees on the property. The only resolution until harborages are found is to fog the structure to kill existing adults and make certain the structure is sealed.

ANSWER:

The Black Polycaon - Polycaon stoutii - is an anomaly. It is one of our larger wood infesting beetles, with adults about an inch long. It currently resides in the family Bostrichidae with the "false" powderpost beetles such as Lead Cable Borer and Bamboo borer, but looks very different from them. Instead of having its head tucked under the overhanging prothorax the head of the polycaon is very large and sticks straight out in front. The legs are long and obvious and it has an overall elongated, cylindrical shape.

Apparently this beetle, which is found only in the western states, has the potential to cause some damage to indoor wood materials, and plywoods (oddly) seem to be the most often attacked. However, I have also seen adult beetles emerging from hardwood furniture such as oak arms of couches, and this suggests that it is likely the furniture was infested by a female beetle depositing eggs on it after it was built. There also have been two occasions where large numbers of the adult beetles were found on or in buildings where it did not appear that anything made of wood was infested, but only that the adult beetles were drawn to the location for some reason. My suspicion was that they were attracted to odors in the area - on on top of a hospital roof and another in a chemical warehouse.

However, if you are continually finding these indoors that really is suggesting that there is an indoor source. The adults are attracted to lights, but a medical office would not be likely to be leaving doors open. Adult emergence holes are about the diameter of a pencil and very round, so they are obvious if located in an exposed place and your inspection should find them. Perhaps the adult beetles emerged from some hidden location and the adults worked their way out so that you cannot easily see these holes. It would seem less likely that the adult beetles are going to some trouble to find access points around the structure to work their way inside, and more likely that they are emerging from something inside the structure. I don't think they infest living trees, so those conifers outside should not be the source. The presence of that one in the attic is interesting, and I would consider it more likely the adult beetles would find their way down FROM the attic to the lighted areas below than it would for them to move from below up into the dark attic. Their instinct as the adult beetle is to move to light and to escape the structure.

The beetles do attack hardwoods or softwoods, including plywoods, when the wood is in storage. Perhaps in this case they infested stored lumber that was then used to construct furniture or cabinets in the building, so your inspection should have some focus on what NEW wood products have come into this office. It may be that you will find something that can be removed and either treated independently or disposed of. If the infestation is within materials built in that becomes a different decision, and it would not be common for them to continue to reinfest in the manner that powderpost beetles do. This infestation could be self-limiting.

I'd be careful of fogging the building very often, since this is a sensitive location as a medical office. Fogging with pyrethrum also may not be very effective on these large and sturdy beetles. The best option, and easy for me to say and harder for you to do, would be to continue the intensive inspection to try to find the source, and once found then determine if there are any more beetles to emerge or how that wood may be treated to prevent the problem from continuing.

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