Wood shavings below furniture usually means some hungry insect is feeding. There are several insects that damage wood, and the damage they cause differs by region and climate. Subterranean and drywood termites, for example, are more of a problem in warmer climates. If you're in a region where the climate is cooler, you are probably more concerned with carpenter ants. In coastal areas where the climate is damp, wood borers may be the culprit.
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Termites are often the first insect that comes to mind when people are dealing with wood damage. Termites leave wood shaving beneath furniture, but other evidence of infestation includes termite droppings and exit holes in the wood. These small bugs build colonies inside of the wood and eat away at the wood fiber so the damage is usually not seen right away. By the time the damage is done, it's pretty far along. They generally attack and infest softwood. Mud shelter tubes provide evidence of termite infestation. Although termite infestation can occur in numerous climates, they are especially active in tropical climates.
Carpenter ants are not always as damaging as termites, but if they are left to do damage for a long time they can accomplish a lot. They don't eat the wood as some insects do, but they burrow in to build their home. Evidence of carpenter ant infestation is the presence of wood shaving or frass beneath the furniture. The wood shavings will contain insect parts. Carpenter ants are reddish-black and build their nests in cavities above the ground. The nests have no emergence holes, but the ants enter and exit the colony to forage for food and water.
Two powderpost beetles that damage wood are the Lyctid and Anobiid. It is the larvae of these beetles that bore into the wood and feed on starch. Both are small reddish-brown to black insects, but they have several differences. The head of the Lyctid powderpost beetle is visible from above, but the head of the Anobiid is not. The Lyctid destroys mostly hardwoods such as flooring, furniture and cabinets; the Anobiid destroys mostly softwood and is especially active in damp climates. Evidence of both is very fine powder. The Lyctid leaves dusty powder and the Anobiid leaves a powder that is gritty.
Round-headed and flat-headed wood borers are differentiated by the holes they make: one circular to oval and the other flattened to oval. The wood shavings left by these insects are either powdery or gritty. The round-headed beetle has a distinct capsule-shaped head, while the larvae of the flat-headed beetle sometime have a flattened region behind the head. Both eat hard and soft woods. Neither of these beetles commonly infests old wood or wood that has already been infested, so the damage is limited to the first generation; the next generation will move on to infest wood that has not yet been infested. The insects are also different in their appearances. The round-headed beetle has long antennae and is colorful; the flat-headed beetle has metallic coloration.