Adult beetles do not eat wood, only the beetle larvae do. When you see holes in either structural wood or in furniture, it is because the larvae have already left and you are seeing the exit holes. This could be an indication of a nearby infestation. Generally, beetles are attracted to the same type of wood from which they were born.
Other beetle species feed on garden plants, such as the Colorado Potato Beetle, the Boll Weevil, the Rose Chafer, the Western Corn Rootworm, and many more. Each of these beetles can cause millions of dollars in damage to crops of many different kinds. The presence of just a few beetles usually indicates that more exist, so it is best to contact a qualified Pest Control agency.
Some beetles, such as the common Ladybug, are actually advantageous to have around. They are known to keep down the population of other insects, so you should not attempt to destroy them or any other beneficial beetle species.
Treating for beetles requires proper knowledge of the type of beetle species you are trying to eliminate. Wood eating beetles, for instance, cannot be effectively treated using sprays because they are located deep within wood. If you think you may have a beetle infestation, your local pest professionals will have the knowledge,resources and solution to the problem.