Moved from Hornets and Yellowjackets.

Andy's ID is quite correct, and the two workers in the middle are V. flavopilosa too, based of the color-pattern of their last tergite (compare with V. maculifrons, where the V-shaped yellow edge is much narrower).
A really interesting case of relatively peaceful relations between such agressive insects. It must be believed there is enough sap for everybody!
One can notice, however, how the outnumbered V. squamosa worker superbly ignores its three V. flavopilosa neighbours, while these latters seem to "wait" for its departure to take their turn. It could well have chased one or several of them from the main "source".
Obviously, V. squamosa is the dominant species, while V. maculifrons doesn't even try to compete with the two others.

My first impression was that it was a nest entrance, but there appear to be at least three different species here. V. maculifrons (at the bottom), V. squamosa (top left), and V. flavopilosa (top right). Can't see enough of the two in the middle to identify them.