Spiders are not wood boring insects; however, they very well could under plywood or inside existing holes. If you have a critter boring into your wood, it could be powder post beetles, carpenter ants, or termites. Active boring would generally leave behind sawdust looking wood particles known as frass or even a fine wood powder. The best product for this type of treatment is
Boracare. Boracare can be applied only to bare - unpainted and untreated - wood. You dilute the product down with water and either spray or paint it onto the wood. It absorbs in and will kill any existing infestation of wood boring insects and will preventfrom future infestations for the life of the wood. You need to verify exactly what type of insect you are dealing with though to know if Boracare is right for you or if you need a different type of insecticide. An excelent product for spiders is
Demon WP.