Pictured is a section of an oak floor joist that I simply tore loose with one hand like cardboard!!  There were tens of these, and I could have easily brought out many large sections had I wished to do so.  This is always a sad situation for me to see.  Possibly the builders did not use kiln dried lumber, and maintain adequate ventilation.  The home was otherwise well built in the style of the mid 1900’s.  The damaged could have been reduced or prevented at any time over the last 50 years, but obviously no professional was ever called to perform even the most basic inspection.  Now the damage is done, and my recommendation for this home was primarily to replace 50% of the floor joists with pressure treated lumber, requiring large costs in material and labor.  In this case, I decided I wouldn’t treat for the beetles until the joists were replaced due to the severity of damage.