If you look closely at this picture, you’ll see little holes in the wood. These are anobiid beetle exit holes. Elevated moisture conditions in wood leads to WDO (wood destroying organism) activity and damage.  Insect damaged structural elements like these are typically replaced, depending on the severity of damage.  When replacing exterior deck structural elements, I highly recommend using pressure-treated wood products to prevent WDO activity and extend serviceable life.  Untreated exterior elements will deteriorate over time and are at risk of WDO damage. This was discovered at a recent home inspection in Friday Harbor on San Juan Island.