I agree it is wash boarding but my understand is they don't no why they do it. My bees we doing it a couple days back when it was so hot, but we are in the biggest flow of the year.Don, that is known as washboarding. It is what the foragers do when they are bored. Too hot for them inside the hive and nothing to collect in the field. At least, that is my understanding of the behavior. Just think of it as the bee version of line dancing!