The aircraft had been parked in a hangar and not flown for six months until the day before the accident. After landing on that occasion the pilot noticed that the airspeed indication was slow to return to read zero. The next day the pilot believed the airspeed took longer than usual to reach the normal cruise indication. When on final, with an indicated airspeed of 80 kt the stall warning light illuminated, the aircraft stalled and struck the ground. Prior to the second flight the pilot had attempted to clear the pitot/static system by blowing into the pitot tube. Inspection of the static system found evidence of a blockage by an insect nest. The blockage was in such a position that it would not have been visible during a preflight inspection.