I don't have a good answer to your question of why they would be so aggressive 20' from their hives. The only thing I can attest to is that, when using Apiguard (Thymol) in my hives, my bees become very annoyed and aggressive. They work furiously to remove the Thymol from their hive and I have even had a hive abscond when I attempted to use Thymol. My understanding is that the fact that the Thymol is an irritant to the bees aids its spread of the Thymol through the hive as bees work hard removing it, thereby spreading it all over themselves and their hive mates.
However, that would not really explain why bees would be aggressive in a thyme herb garden 20 feet away from the hive. Seems they would simply avoid the area if thyme, in its natural state, was also an irritant. I suppose you have checked and made sure that no swarm has made a home under the big pillows of dead wood?
However, that would not really explain why bees would be aggressive in a thyme herb garden 20 feet away from the hive. Seems they would simply avoid the area if thyme, in its natural state, was also an irritant. I suppose you have checked and made sure that no swarm has made a home under the big pillows of dead wood?