Each fall as we cut firewood and bring it into our homes, we also may be bringing in some unexpected hitchhikers. There are many insects and other arthropods that may be living in your firewood. Luckily, most insects living in firewood pose no danger to humans, our homes, or our furniture. Insects in firewood are either feeding directly on the wood, nesting in the wood, or are overwintering under the bark.
The best way to prevent the insects from emerging from firewood in your house is to leave the firewood outside until it is to be burned, bringing at most, a few days' supply into the house at one time. Insects in firewood stored outdoors generally require several days to warm up in your home before they become active.
Spraying firewood with insecticide is of very little benefit and potentially dangerous. Therefore, we strongly advise against treating firewood. Insecticides will not penetrate deeply enough into firewood to control the insects. In addition, storing and burning insecticide-treated firewood indoors could be a health hazard if the insecticide is vaporized into the living area of the house.
Two insects that may cause problems if you keep your firewood stacked against the outside walls of your house are carpenter ants and termites.
Wood that remains moist for an extended period is a likely candidate for infestation by carpenter ants. Carpenter ants do not feed on the wood, but they hollow out galleries in the wood for nesting. The galleries are smooth and go with the grain of the wood. If infested firewood is brought into the house the ants may warm up and move out of the wood. Although an annoyance, the chances of these ants establishing a nest in your house are very slim. Stacking wood against the outside of your home may provide an avenue for these insects to enter your home.
Wood that is stacked directly on the ground may be fed upon by termites. Mud tunnels may be visible on the outside of the wood, or there may be mud-lined galleries within the log. The main termite nest containing the queen is in soil, but the workers will tunnel into the firewood and feed on it. Termites brought into your home in firewood cannot establish a new nest and will not damage your home or furniture. But, as with carpenter ants, wood piles stacked against the house can provide a way for termites to extend their feeding into your home.
Stacking firewood off the ground is the best method to prevent termites from feeding on your firewood. If you discover a termite infestation in firewood stacked next to your house you should have your home treated or inspected by a pest management professional.
There are several groups of beetles that feed on wood and can accidentally be brought into your home in firewood. These beetles can be a nuisance if they emerge from firewood; however, none of these beetles will harm your home or furniture.
Longhorned beetles are attracted to dying, freshly cut, or recently killed trees where females lay eggs on the bark of the green wood. The larvae (commonly called roundheaded borers) emerge from the eggs and burrow into the tree and spend 1-3 years tunneling through the wood. Tunnels may be just under the bark or in the heartwood, are usually about the size of a lead pencil, and are packed with coarse sawdust. The larvae are wormlike and white to yellowish with a brown head and round body that is deeply wrinkled. Holes and piles of sawdust mark where the adult beetles emerge from the infested wood. These beetles get their name from their long antennae that are half as long or longer than their bodies. In Iowa, adult longhorned beetles commonly range from 1/2 to 1 1/2 inches in body length. Many are attractively colored with yellow stripes on their bodies.
Metalic wood-boring beetles
The larvae of these beetles are called flatheaded borers because they have a large, flattened head. They are similar to the longhorned beetles in that the larvae bore into wood, pupate, and adults can emerge from firewood stored in homes during the winter. These beetles have short antennae, often have a metallic sheen, and are somewhat bullet shaped.
Bark beetles often attack dead or dying trees. This characteristic makes them common in firewood that is cut from dead trees. These bettles are small (less that 1/8 inch in length), brown or black and cylindrical. The adult beetles tend to attack wood in groups and so a log cut from a tree that they are feeding on can contain hundreds of individuals.
There are a variety of insects that spend their winters under the bark of trees or in your wood pile. When you bring firewood into your house and it warms, these insects crawl out of the wood. Pillbugs, centipedes, millipedes, ground beetles are commonly found in firewood. They will not harm you or your house and need only be picked up and removed.
This article originally appeared in the March 7, 2003 issue, pp. 21-22.
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