This is the first year I've ever noticed yellow jackets building exterior nests in shrubs. Ran into one last Friday and 3 today. And before you tell me it's not yellow jackets, they are. I know my wasps...
I frequently notice exterior yellow jacket nests under railings, in mailboxes, window frames, etc etc, but I have never seen on in shrubs. I swore the one on Friday was a wasp nest because it was a perfect round gray ball a little smaller than my head. But I watched it closely and alas...yellow jackets were going in and out of it. I found 3 small phone-sized honeycomb yellow jacket jests (The kind I typically find under railings and whatnot) today, but they were easy to take care of.
so my point is that it's very possible for yellow jackets to build nests in shrubs, so start by looking on the tips of the branches for a fist-sized or smaller honeycomb nest.