I don't really know why they do this, I just know they do. For whatever reason, this year they seem to be more obnoxious than usual, and we've been having a rough time with them for the last couple of weeks.
I looked online and there are all sorts of ways you can "upcycle" old pop bottles and such to lure them away from your outdoor dining area but since we don't drink pop, I decided I wasn't going to do one of those crafty things. So off to the store I went to find some kind of yellow jacket trap that actually worked (I'd never used one, so I wasn't even sure what to get).
The instructions said to fill half-way with sugar water or pop, then hang away from where people gather. So, I did that but I used sugar water. It worked so-so, but not like I wanted it to. So then I bought a bottle of Sprite and used that. It worked a little better, but still not as well as I'd hoped. So then, I decided to get some fruit juice (apple juice was on sale for a dollar, so that appealed to my cheap-side) and try that.
Well, I filled them half full of apple juice, moved them over to the fence on the side of the house and OH MY GOODNESS! Within minutes, yellow jackets were swarming all over both of them and there wasn't a single one on the patio. I went out again just moments ago to get this picture and there are already numerous little buggers inside them. Still none on the patio.
Now, we haven't had a meal on the patio yet with the traps out there so I don't know if they're a powerful enough draw to keep the beasties away from the food, but for now, it's working.
So do yourself a favor if you're looking for a solution to getting rid of these pesks, and don't want to spend big money. Either make your own (google it, there are pics all over how to do it) or get the cheap little jars and fill them with fruit juice.