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Beetle Damage in Log Homes

By Chris Williams on November 11, 2015.
old house borer

Wood-boring beetle larva inside tunnel

My wife and I just bought a log cabin as co-owners with my brother-in-law. Although we inspected it prior to the sale, we didn’t notice oval-shaped holes in the logs in the back bedroom until we stayed there last week. I’m guessing that means that our cabin has wood borers! What should we do? F. N., Clinton, MA

First, don’t panic. The oval holes mean that the logs have been infested by wood borers at some time, not necessarily that they are still infested. What you saw are beetle exit or emergence holes, left when the newly transformed adult beetles leave the galleries inside the wood.

The Beetles May Be Gone…or Maybe Not

Oval-shaped emergence holes in log cabins usually belong to a group of beetles that attack wood shortly after it is felled. Eggs are laid in cracks in the wood and the larvae feed in galleries inside the wood, usually for two years or more before emerging as adult beetles. Most of these beetles need a high wood moisture content and so do not reinfest wood once it has dried and seasoned. In these cases, the infestation is limited and the exit holes are old.

You don’t say how old your cabin is. If it’s only a few years old, the infestation could still be current and more beetles may yet emerge. If the cabin is considerably older, any beetles have probably long emerged and any limited damage has already been done, with one exception. There is one wood-boring beetle, called the old house borer, that can reinfest seasoned softwoods, especially in a home or cabin that is unoccupied for periods. Old house borer larvae usually complete development in 2-3 years, but may take much longer. If conditions are right, eggs can again be laid in wood in the structure resulting in another generation and more damage.

Some Signs That Beetles Are Still Feeding in the Logs

1. chewing or scraping sounds coming from the wood – these sounds can be heard from large, fully mature larvae as they feed inside wood.

2. new emergence holes – you can mark or take photos of existing holes so that you will know if new ones appear.

3. frass beneath emergence holes – if the emergence holes are old, presumably the frass (which looks like sawdust) that is pushed out of the galleries will have been swept up. The presence of new frass below an exit hole indicates that a beetle has exited or or is about to emerge.

4. adult beetles – these beetles are about one inch long and usually emerge from the wood in July-August in our region. They often fly to lights or windows but may not even be noticed in small numbers.

You should have a pest control professional take a look at your cabin. An inspection should be able to determine whether beetles are still active. If so, there are a number of control options ranging from surface application of a borate insecticide to wood injection to fumigation. If the infestation is limited to a couple of logs, replacing damaged sections is also a possibility. Give Colonial Pest a call today!

For more on wood borers in log homes, see these blogs:

Photo credit: Wikimedia Commons

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