Insect Problems in Log Homes

We get a lot of questions from log homeowners concerning insects; sometimes insects they have discovered in their homes already, or from homeowners trying to be proactive about potential insect damage.

It is true, that being built of wood, log homes may have potential problems with insects such as termites and carpenter ants that can cause structural problems. But there is no evidence that this is any more of a concern than it would be in a wood frame home.

Flies may certainly be an issue in log homes; this is most typical in certain areas of the country, in new homes, and in homes that have not been well sealed.

Here is our advice on some of the most common insects you may find in your log home:

Carpenter Ants

Carpenter ants differ from termites by having dark-colored bodies, narrow waists, elbowed (bent) antennae, and hind wings shorter than front wings (if they have wings). Carpenter ants are very common and are frequently seen in the open. They feed on protein and sugar and do not eat wood. They only remove wood as they create their homes in the wood.

Carpenter ants are kind of like the ‘canary in the coal mine’: if you have carpenter ants nesting in your home, then you almost certainly have rotting wood in your home. Carpenter ants nest in moist or decayed wood; they are unable to chew (tunnel) through sound, solid wood.

You may also have carpenter ant nests outside of your home in rotting trees, stumps or old lumber piles. In this case, you may see them in your home when they are foraging. When you clean up that debris outside, which might be the only solution needed, you may solve the problem entirely.

It is sometimes hard to know whether the ants are nesting inside or outside the building. If you find carpenter ants in your home in winter, they are most likely nesting inside the building. Finding a lot of winged ants indoors is also a good indicator that the ants are nesting inside the house. (A few ants may come in with firewood during the winter.) To find the colony: look for small piles of sawdust or set out bait (small pieces of meat or other protein) and patiently follow the ants. Small children are good at this.

You may choose pest control products to eliminate the ants temporarily, but the ants will go away permanently only when their nesting sites are eliminated. No insecticide will remedy the problem of moisture in wood; only structural repair will take care of that. . . . and will also save your home from a lot more damage from moisture and decay. We have had carpenter ants in our home twice; once indicating a skylight was leaking and another time indicating failed flashing on a stone chimney. When the structural repairs were made, the ants were gone.

We recommend that you contact a professional pest control company for application of insecticides. A professional contractor, perhaps along with a building
inspector, should be consulted to examine the problems of structural moisture damage.

Carpenter Bees

Carpenter bees are large black and yellow bees that may be mistaken for bumble bees, often seen under the eaves of the house or under a deck. (They differ from honeybees in that they have a shiny black tail section.) They are more often found in the southern states than the northern states. Like carpenter ants, carpenter bees excavate tunnels in wood for their nests. Unlike carpenter ants, they can more readily excavate sound wood, especially unpainted wood, weathered wood or softwood species.

Look for round half-inch diameter holes with a telltale trace of coarse sawdust underneath it. The female bees excavate the holes to lay their eggs and they do not form colonies. They just have a lot of children, who move out but still stay in the neighborhood. They seldom become numerous enough to cause structural damage.

A non-insecticidal approach can be used to eliminate carpenter bees. Seal each entrance hole with caulking, forcing the caulking back into the tunnel as far as possible.

A preventative approach may be taken by applying a coat of wood finish containing Bug Juice, a contact insecticide that will kill the bees when they walk on the treated wood surfaces. This is best done in the early spring when the bees become active. Unfortunately, this type of poison also kills honeybees and other beneficial insects. Use it only as a last resort. Insecticides that act as stomach poisons, such as borates, are not effective, as the bees do not ingest the wood they excavate.


Termites resemble large ants, but are light colored, have straight antennae, and have no waist constriction. They avoid light and are rarely seen outside their colony, except when they develop wings and swarm to start new colonies in the spring.

Discovering winged termites indoors is almost always a sign of a termite infestation. Other signs are earthen (mud) tubes, usually about the diameter of a pencil, extending over foundations, floor joists, etc. Often there will be no visible signs that the building is infected, and a professional inspector should be consulted. Control of termites requires special skills and is best left to professionals.

The best approach to preventing termite damage is to prevent termite infestation from the onset with good design and construction. Keep the ground around the foundation dry with the use of gutters, sloped ground, and drains. Reduce humidity in the crawl space, attic, bathrooms and laundry rooms with proper ventilation. Remove tree stumps and wood debris from around the building and keep shrubbery and trellises, etc. away from the building. Eliminate any wood contact with soil; an 18” clearance is ideal.

Borate preservatives may be used to help protect against termites, but are no guarantee if the termites can tunnel over the treated wood to another entry area. Termite entry can also be gained through checks, gaps and cut or cracked wood ends.

Cluster Flies

The Cluster Fly is the number one annoying insect problem in many log homes. Cluster flies are not the common houseflies; they are slightly larger and belong to a different genus (Pollenia rudis). Cluster flies are very common in the fall when they are trying to find protected sites to spend the winter. You will find them on sunny walls outdoors, and in sunny windows on the inside of your home. You might even find hundreds of them on a warm sunny day autumn day. We find they most prefer to come out in droves when we’re having a dinner party, circle the light over the dining room table, buzz loudly for three or four loops, and then make an ungraceful landing in a dinner plate. (They are not known to carry any diseases, and may be considered a source of minerals and protein.)

Contrary to belief, they are not reproducing inside your home. Cluster flies lay their eggs outdoors on the soil surface and the larva burrow into the earth to feed on earthworms. This goes on all summer long, and only when the weather begins to turn cold do the current generation of flies seek a nice protected site to spend the cold winter.

Sealing up your home is the best way to keep cluster flies from entering. Cracks around doors and windows, underneath the fascia, around exhaust fans and ceiling fixtures, checks in logs, log ends, and any other openings should be diligently sealed with good-quality chinking or caulking. When caulking log joints, experience has proven to us that tiny beads of caulking do not do the job. A caulking line of at least 1/4” in width is an effective long-term solution.

Many log homes built in the past, and even some being built today, have roof structures that will allow the flies to enter. In a typical log home, the roof system may consist of a ceiling of wood decking, with insulation, plywood and tarpaper on top of that, finished on the outside with shingles or metal roofing. If the joints in the plywood were not carefully caulked, this is going to be a roof that will allow a lot of flies to penetrate into the inside. Most contractors today will seal all the joints in the roof structure as it is built, ensuring that there are no tiny cracks or fissures left unsealed.

Insecticides such a synthetic pyrethroid may offer some relief when applied to the exterior openings in the home. They are most effective in the fall, just prior to fly congregation. Because these materials break down quickly, especially in sunlight, they do not last long and will have to be reapplied often. It is not realistically possible to kill flies that have already hidden in wall voids or in the roof structure. Aerosol type pyrethrum foggers are not effective in these areas and are not recommended. You can only kill them when they come out to visit: I use a food service safe pyrethroid aerosol when they get too abundant, a fly swatter otherwise.