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Log Homes & Wood Boring Insects

- Insects like log homes too -

Summary: A number of insects bore into the fresh logs, or standing trees, that will become log homes. These wood boring insects feed on the starch reserves stored there by the living tree. Fortunately only a few wood borers do significant damage because most can't infest seasoned wood. Extensive damage can be avoided with relatively inexpensive treatments.

Jack DeAngelis, PhD

OSU Ext. Entomologist (ret.)

Which insects damage log homes?

There are a number of insect larvae that tunnel in dead trees or freshly cut logs. The larvae feed on starch reserves in the wood that were formed when the tree was alive. Recently dead trees, rather than older seasoned wood, are more susceptible to infestation because they contain better starch reserves. On the other hand, most of these insects cannot infest live trees because of their natural defenses.

Adult insects lay eggs on the wood surface. Larvae bore into and tunnel the wood weakening the fibers and opening the wood to moisture and rot fungi. In most cases, once the first generation of insects emerge the wood is too old to be re-infested.

Large wood borer larva. Head end is on left. Despite the size of these larvae, up to several inches, damage is limited because they do not re-infest.

In some cases trees that are destined to be logs of a log home become infested while they are still in the forest. In other cases logs become infested after they are debarked and used in construction. In either case it is important to prevent infestation before extensive cosmetic and/or structural damage is done. Fortunately there are relatively inexpensive ways to prevent this damage. The main wood-boring insect pests of log homes are: long-horned beetles, flat-headed wood borers, and powderpost beetles and it is only the powderpost beetles that pose a serious long-term threat.

Longhorned beetles

Larvae of longhorned beetles are sometimes called round-headed wood borers. Adult beetles [photo of longhorned beetle] have very long antennae from which their common name, "longhorned beetle", is derived. Larvae are legless, white grubs with reddish/brown head capsules (see photo above).

Longhorned beetles generally only infest fresh wood and will not re-infest the wood from which they emerge, which limits their potential for damage. Log damage is limited to large bore tunnels and circular to slightly oval emergence holes which should be filled with caulk to repair. Generally no insecticide treatment is needed (see Which Insects Damage Wood?).

Flat-headed wood borers

Flat-headed borers belong to the beetle family Buprestidae. Adult beetles are sometimes called metallic wood borers [photo of metallic wood borer] because of their showy coloration. The larvae are similar to longhorned beetle larvae (above) except that the area behind the head is somewhat flattened. Like longhorned beetles these wood borers do not re-infest and thus their potential for damage is limited. Emergence holes are flattened oval in shape.

Powderpost beetles

Powderpost beetles are the only wood borers that commonly re-infest seasoned wood and therefore have potential to do long term damage. The powderpost beetles that infest softwood timbers are usually in the family Anobiidae (see Exterior Log Home Care).

Other wood damaging insects

Carpenter bees --These large dark colored bees bore into wood to construct a nest chamber. These chambers may be enlarged year after year. The holes and nest chambers made by carpenter bees may allow water and rot fungi to attack the wood (see What are Carpenter Bees?).

Like any wooden structure log homes are subject to termite and carpenter ant damage as well as the other wood boring insects described here. Keep in mind that water, because of its potential to cause rot, is the most serious threat to your home and annual inspections will reveal many potential insect and water problems before they get out of hand.

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Jack DeAngelis, Ph.D.

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