I saw a couple of flaming arrows made from kerosene soaked rags tied onto target arrows work pretty effectively on a large paper hornet nest once. That was kind of fun too.
They all used the koi pond to pick up water, I could not enjoy the pond.
Whipped out the wet dry shop vac, and had a great time vacuuming them up around the waterfall.
The bounce off the barrier at the end of the hose and splat themselves.
New roof greatly diminished their numbers!