My kid got stung 14 times by em yesterday when we were fishing.
Goddamn ground nest in the soft river bank of a heavily walked area. No visible opening, really. Maybe 6 inches from waters edge.
There were a bunch of people walking near or over it, my kid just happened to kneel down right on top of it. They didn't swarm, only a maybe 4 or 5 attacked but they went for multiple stings.