by Lee Townsend, Extension Entomologist
University of Kentucky College of Agriculture
Many people use a fireplace to supplement their heat supply or just for enjoyment. Insects and other arthropods that are brought into the home on or in firewood may cause alarm but most are of no consequence. Firewood insects usually belong to one of two groups:
- those that actively feed on wood and
- those there only for shelter.
Wood Infesting Insects
Many insects attack dead or dying trees. Their activities ensure that the resources in the wood are broken down and recycled. Beetles are the most common group found developing in firewood. These include roundheaded wood borers, flatheaded wood borers, and shothole borers, also called powderpost beetles. The legless, white larval stages of the first two types can be found while splitting logs. Piles of sawdust appear from small holes in logs infested by powderpost beetles. The potential for these insects to infest structural wood in the house is very low. Often these borers attack only certain types of wood, such as hickory or oak. Also, the moisture content of the wood usually has to be much higher that than found in structural wood in the home. Sometimes the adult emerges after logs are brought indoors. Roundheaded wood borers are brightly marked, fast beetles with long antennae. The elongate flatheaded woodborers often have a metallic sheen. Powderpost beetles are small, brown to black insects. Any of these may be seen crawling or flying in the room or accumulating at windows or light fixtures as they move to light. These insects are harmless. Carpenter ants and termites may also be found in firewood that has been wet or stacked in one place for a long time. Termite colonies are in the soil so only workers are found in the wood. Termites form mud tunnels and this mud can be found in wood that they are attacking.
Carpenter ant galleries are very clean, with no mud or sawdust. Individuals brought into the house in logs will not start an infestation but a colony may exist in old wood piles outdoors.
Many insects seek overwintering sites under loose bark or in hollow trees. Possibilities include many types of beetles, wood cockroaches, and even overwintering wasp or hornet queens. Spider egg sacks, praying mantid egg masses, and moth cocoons are part of the "fauna" that may be associated with trees or fallen logs. These creatures will become active after warming up indoors. These can be swatted and discarded as they appear. These insects are not able to survive for extended periods indoors. They will not multiply or become established in the home.
Insect invasion of homes from firewood can be reduced by following these rules:
- Avoid stacking the wood directly on the ground. This will keep the wood from getting too wet and reduce the chances for infestation by termites and ants.
- Don't stack firewood in or against the house or other buildings for long periods of time. Termite or carpenter ant problems can develop and cause more serious problems.
- Use the oldest wood first, it is most likely to be infested. Avoid the tendency to stack new wood on top of old wood.
- Cover the wood during the summer and fall. This will keep it drier and exclude some creatures seeking overwintering sites.
- Shake, jar, or knock logs together sharply to dislodge insects and brush off any obvious structures such as webbing or cocoons before bringing it inside.
- Bring in small amounts of firewood that can be used up in a day or so and keep it stacked in a cool area (e.g., garage or porch) until it is burned. When wood warms up, the creatures in or on it will become active.
- Do not treat firewood with insecticides. It is unnecessary and potentially dangerous due to fumes that may be produced when the insecticides burn.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!