I learned the hard way that you don't let hornets build a hive. We had some in the yard a couple of years ago. I tried to take a live and let live approach, but it didn't work out. the father in law took a couple to the head and neck, so we went to war. Four cans of hornet killer later and there were bodies everywhere. We were hitting them in the air, on the ground, and down the hole. After the battle, we were surveying the wreckage, when I heard the sound of a chopper coming in from the left. I braced for impact, and felt the searing, vibrating burn as the assassin exacted her vengeance on me. I never saw the assailant, but the damage was done. Three days of a swollen neck and a week of pain. Never again I cry, NEVER AGAIN! All hornets must die! :0)