Honey bees regulate the internal temperature of the hive to keep it in the mid nineties (°F).
Bearding is one of their HVAC tools:
On hot days, they may congregate outside to help cool the inside.
The beard usually dissipates overnight—for these hives, anyway.
You can hear a subdued, calm buzzing if you get close enough to the side;
they are not especially aggressive.
In a gentle breeze, a thick beard like this pleats a bit like fabric.
I also witnessed this hive's beard remain largely in place through the windswept squalls of
a nasty thunder storm.
(Some beekeepers with a penchant for panache also coax bees into bearding on their faces
to entertain onlookers. I remain clean shaven.)