Bald-faced hornet nest? - Dolichovespula
Bobolink Trail, Boulder County, Colorado, USA
August 27, 2015
Size: 20-odd cm?
You have oodles of pix of bald-faced hornets, Dolichovespula maculata, so I will not bother you with another. But cd this be their nest? Was perhaps 5-6 m above ground. This pic very nicely shows the hexagonal comb structure within.